Class 10th Science Gujarat Board Solution
Exercise- What is the chemical formula of alumina?A. Al2O3 B. Al2O3. 2H2O C. Al2O3.H2O D. NaAlO2…
- Which of the following reactions is called roasting?A. ZnCO3(s) ZnO(s) + CO2 (g) B.…
- Which of the following is an alloy?A. Silver B. Gallium C. 22 carat gold D. 24 carat gold…
- During which reaction dihydrogen gas is not produced under normal conditions?A. Metal +…
- In which of the following, displacement reaction is possible?A. Solution of NaCl + coin of…
- Which of the following is not possible?A. Zn(s) + CuSO4 (aq) ZnSO4 (aq) + Cu(s) B. Zn(s) +…
- By which reaction metal is obtained from metal oxide?A. Liquefaction B. Reduction C.…
- Which of the following statements is incorrect?A. Corrosion of copper takes place by…
- Which alloy is used to solder the electric wires?A. Copper + zinc B. Aluminium + magnesium…
- Which metal is available in highest proportion on the earth?A. Iron B. Copper C. Aluminium…
- Which metal is used in thermometer?A. Silver B. Mercury C. Sodium D. Copper…
- Which of the following substances is hygroscopic?A. Cryolite B. Feldspar C. Anhydrous…
- In which three sections elements are classified?
- Which metals are available in free state in nature?
- In which form ores are available in nature?
- Write names and formulas of two ores of iron.
- Write names and formulas of two ores of copper.
- Write names of the three methods for concentration of ores.
- Which two methods are used for reduction of metal oxides?
- Write names of three methods used for refining of metals.
- What has been taken as anode and cathode for refining of metals in electrolysis method?…
- Which chief impurities are present in bauxite?
- Which two substances are added along with alumina to obtain aluminium from alumina by…
- Which substance is called slag?
- Mention use of slag.
- Which general principle is taken into consideration in determination of activity series of…
- Mention names of two softer metals.
- Write names of two metals which are bad conductors of electricity.…
- Write names of two metals oxides which form alkali by dissolving in water.…
- Which two metals burn with explosion in reaction with water?
- Which two metals are generally not corroded?
- Stainless steel is a homogeneous mixture of which three metals?
- Write chemical formula of rust.
- Mention the formulas, names and physical states of the products in the following…
- Describe the method to remove impurity of iron from ore.
- Explain the method of concentration of copper pyrites - the ore of copper.…
- Explain the refining of copper by electrolysis.
- Write four physical properties of metals.
- Mention the components and uses off brass and bronze.
- Write a short note: Earth - Treasure of elements.
- Explain different methods of concentration of ores.
- Explain roasting, calcinations and smelting.
- Explain chemical reduction and electrochemical reduction.
- Explain liquefaction and zone refining method for refining of metals.…
- Discuss the extraction of aluminium from bauxite.
- Explain extraction of iron from haematite.
- Write the activity series of metals. Discuss the experiment for determination of activity…
- Discuss chemical properties of metals.
- Mentioning reasons for metallic corrosion describe the remedies to prevent it.…
- What is an alloy? Mention its advantages. Mention the name of three alloys and also…
- What is the chemical formula of alumina?A. Al2O3 B. Al2O3. 2H2O C. Al2O3.H2O D. NaAlO2…
- Which of the following reactions is called roasting?A. ZnCO3(s) ZnO(s) + CO2 (g) B.…
- Which of the following is an alloy?A. Silver B. Gallium C. 22 carat gold D. 24 carat gold…
- During which reaction dihydrogen gas is not produced under normal conditions?A. Metal +…
- In which of the following, displacement reaction is possible?A. Solution of NaCl + coin of…
- Which of the following is not possible?A. Zn(s) + CuSO4 (aq) ZnSO4 (aq) + Cu(s) B. Zn(s) +…
- By which reaction metal is obtained from metal oxide?A. Liquefaction B. Reduction C.…
- Which of the following statements is incorrect?A. Corrosion of copper takes place by…
- Which alloy is used to solder the electric wires?A. Copper + zinc B. Aluminium + magnesium…
- Which metal is available in highest proportion on the earth?A. Iron B. Copper C. Aluminium…
- Which metal is used in thermometer?A. Silver B. Mercury C. Sodium D. Copper…
- Which of the following substances is hygroscopic?A. Cryolite B. Feldspar C. Anhydrous…
- In which three sections elements are classified?
- Which metals are available in free state in nature?
- In which form ores are available in nature?
- Write names and formulas of two ores of iron.
- Write names and formulas of two ores of copper.
- Write names of the three methods for concentration of ores.
- Which two methods are used for reduction of metal oxides?
- Write names of three methods used for refining of metals.
- What has been taken as anode and cathode for refining of metals in electrolysis method?…
- Which chief impurities are present in bauxite?
- Which two substances are added along with alumina to obtain aluminium from alumina by…
- Which substance is called slag?
- Mention use of slag.
- Which general principle is taken into consideration in determination of activity series of…
- Mention names of two softer metals.
- Write names of two metals which are bad conductors of electricity.…
- Write names of two metals oxides which form alkali by dissolving in water.…
- Which two metals burn with explosion in reaction with water?
- Which two metals are generally not corroded?
- Stainless steel is a homogeneous mixture of which three metals?
- Write chemical formula of rust.
- Mention the formulas, names and physical states of the products in the following…
- Describe the method to remove impurity of iron from ore.
- Explain the method of concentration of copper pyrites - the ore of copper.…
- Explain the refining of copper by electrolysis.
- Write four physical properties of metals.
- Mention the components and uses off brass and bronze.
- Write a short note: Earth - Treasure of elements.
- Explain different methods of concentration of ores.
- Explain roasting, calcinations and smelting.
- Explain chemical reduction and electrochemical reduction.
- Explain liquefaction and zone refining method for refining of metals.…
- Discuss the extraction of aluminium from bauxite.
- Explain extraction of iron from haematite.
- Write the activity series of metals. Discuss the experiment for determination of activity…
- Discuss chemical properties of metals.
- Mentioning reasons for metallic corrosion describe the remedies to prevent it.…
- What is an alloy? Mention its advantages. Mention the name of three alloys and also…
Exercise
Question 1.What is the chemical formula of alumina?
A. Al2O3
B. Al2O3. 2H2O
C. Al2O3.H2O
D. NaAlO2
Answer:Alumina is the oxide of aluminium (aluminium oxide), which is produced from refining of bauxite.
Question 2.Which of the following reactions is called roasting?
A. ZnCO3(s) 
ZnO(s) + CO2 (g)
B. 2ZnS(s) + 3022ZnO(s) + 2SO2 (g)
C. ZnO(s) + C(s) 
Zn(s) + CO (g)
D. Zn(s) + H2O (g) ZnO(s) + H2 (g)
Answer:Roasting is the process in which sulphide(S-2) containing ore is heated in the presence of excess of air (O2) for a long time and it is converted into oxide.
So, in this question only in option (B) zinc sulphide (ZnS) reacts with the excess of oxygen to form zinc oxide (ZnO).
Question 3.Which of the following is an alloy?
A. Silver
B. Gallium
C. 22 carat gold
D. 24 carat gold
Answer:Alloy is a homogeneous mixture of 2 or more metals or metal and non-metal. In this question we will get the solution by options.
•In option (A) silver is a metal not a mixture and option
•(B) gallium is also metal and option
•(D) 24 carat gold is the pure form of gold but option
•(C) 22 carat gold is an alloy which consists of 22 parts of gold and 2 parts of other metals such as copper or silver. So, the correct option is (C).
Question 4.During which reaction dihydrogen gas is not produced under normal conditions?
A. Metal + dilute sulphuric acid
B. Metal + dilute hydrochloric acid
C. Metal + dilute nitric acid
D. Metal + water
Answer:Let us take all the options from start.
•In option (A) if metal reacts with sulphuric acid salt of corresponding acid and dihydrogen gas is formed and same thing happens for option (B) also.
•When metal reacts with nitric acid it does not produce dihydrogen gas instead of that oxide of nitrogen is formed because nitric acid is strong oxidising agent.
•So, the correct option is (C).
•In option (D) when metal reacts with water metal hydroxide or metal oxide and dihydrogen gas is formed.
Question 5.In which of the following, displacement reaction is possible?
A. Solution of NaCl + coin of copper
B. Solution of MgCl2 + coin of aluminium
C. Solution of FeSO4 + coin of silver
D. Solution of AgNO3 + coin of copper
Answer:According to the activity series copper is more active than silver so the displacement reaction in the (C) option. In other options the solution metal is more active so no displacement reaction can take place.
Question 6.Which of the following is not possible?
A. Zn(s) + CuSO4 (aq) 
ZnSO4 (aq) + Cu(s)
B. Zn(s) + FeSO4 (aq) ZnSO4 (aq) + Fe(s)
C. Fe(s) + CuSO4 (aq) FeSO4 (aq) + Cu(s)
D. Cu(s) + FeSO4 (aq) CuSO4 (aq) + Fe(s)
Answer:In the first three options the metals were more active than the solution so they could displace them but Cu is less active than Fe so it can’t displace it. So, the correct option is (D).
Question 7.By which reaction metal is obtained from metal oxide?
A. Liquefaction
B. Reduction
C. Calcination
D. Roasting
Answer:Reduction is the method in which pure metal is obtained from the metal oxide.
Question 8.Which of the following statements is incorrect?
A. Corrosion of copper takes place by contact with air and water
B. The melting points and boiling points of metals are low.
C. The method to convert carbonate containing ore to metal oxide is called calcinations.
D. The displacement of less active metals from their solution takes place by more active metal.
Answer:If we check option by option then we can clearly see that in option (B) it is mentioned that metals have low melting and boiling points but it is not true generally metals have high melting and boiling point. So, option (B) is correct.
Question 9.Which alloy is used to solder the electric wires?
A. Copper + zinc
B. Aluminium + magnesium
C. Lead + tin
D. Copper + tin
Answer:Melting point of alloy prepared from lead and tin is low so it is used to solder electric wires.
Question 10.Which metal is available in highest proportion on the earth?
A. Iron
B. Copper
C. Aluminium
D. Silver
Answer:Aluminium is the most abundant metal available on earth. It makes up to 8% of Earth’s crust by weight.
Question 11.Which metal is used in thermometer?
A. Silver
B. Mercury
C. Sodium
D. Copper
Answer:Mercury is liquid at room temperature and it is also sensitive to temperature so it is used in thermometer.
Question 12.Which of the following substances is hygroscopic?
A. Cryolite
B. Feldspar
C. Anhydrous calcium chloride
D. Slag
Answer:Hygroscopic is a substance which absorbs moisture from air. Anhydrous calcium chloride is highly hygroscopic that is the reason it is kept in tightly sealed container.
Question 13.In which three sections elements are classified?
Answer:All the elements are classified into 3 sections they are:
Metals, Non-metals and semi metals (metalloids).
Metals: A metal is a material that is hard, opaque, shiny, and has good electrical and thermal conductivity. Metals are generally malleable and ductile.
Non-metals: Non-metals have low melting and boiling points, densities, brittle if solid, and are usually poor conductors of heat and electricity.
Metalloids: A metalloid is an element that exhibits some properties of metals and some of non-metals.
Question 14.Which metals are available in free state in nature?
Answer:Gold and platinum ate the metals available in free state because of their very low activity.
Question 15.In which form ores are available in nature?
Answer:If in a certain mineral metal proportion is more and its extraction is advantageous then it is called ore. Ores are found in combined form in nature such as silicate, carbonate, oxide, phosphate, sulphide, etc.
Question 16.Write names and formulas of two ores of iron.
Answer:The main 2 ores of iron are Haematite its formula is Fe2O3 and Magnetite its formula is Fe3O4. These ores are mainly found in the region of Madhya Pradesh, Tamil Nadu, Orissa, etc.
Question 17.Write names and formulas of two ores of copper.
Answer:The 2 ores of copper are Cuprite (Cu2O) and Copper Glance (Cu2S). These ores are mainly found in the region of Rajasthan and Bihar.
Question 18.Write names of the three methods for concentration of ores.
Answer:Three methods of concentration of ores are:
(i) Concentration or centrifugation on the basis of difference of densities: This method is used when there is large difference in densities of ores and impurities.
(ii) Froth floatation method: This method is used for the concentration of ores of the metals whose ores are in sulphide form.
(iii) Magnetic separation: This method is used when either of ore or the impurity have some magnetic properties.
Question 19.Which two methods are used for reduction of metal oxides?
Answer:Reduction is carried out to obtain metal from metal oxide.
The 2 methods used to reduce metal oxide are:
i) Chemical reduction: When metal oxide is heated in blast furnace with carbon or carbon monoxide, metal is obtained.
e.g. 
ii) Electrochemical reduction: Oxides of active metals such as sodium, magnesium, etc cannot be reduced from carbon because of their more attraction towards oxygen. Hence, electrochemical reduction is used for the reduction of active metals.
e.g. electrochemical reduction of alumina to obtain aluminium.
Question 20.Write names of three methods used for refining of metals.
Answer:The method to obtain about 100% pure metal by removing impurities in very small amounts in metal is called refining.
The three methods used for refining of metals are:
i) Electrolysis: In this method the rod of impure metal is taken as anode and rod of pure metal as cathode. The aqueous solution of salt of metal acts as electrolyte, when current is passed anode dissolves in electrolyte and the same amount of metal is deposited on cathode.
ii) Liquefaction: In this method furnace having a slope is used and the temperature of the furnace is kept higher than the melting point of metal.
When the impure metal is passed on the slope, the metal in it get melted and collected in the vessel but the melting point of impurities is high so they remain on the slope in solid form.
iii) Zone refining: In this method we remove trace impurities which are generally more soluble in molten metal, their solubility decreases as the metal cools and impurities are separated in the form of crystals.
Question 21.What has been taken as anode and cathode for refining of metals in electrolysis method?
Answer:In the method of electrolysis the rod of impure metal is taken as anode and rod of pure metal is taken as cathode. The aqueous solution of salt of, metal is used as an electrolyte. On passing electric current the anode dissolves in the electrolyte and the same proportion of pure metal gets deposited on cathode.
Refining of copper by electrolysis
Question 22.Which chief impurities are present in bauxite?
Answer:Bauxite is the ore of the aluminium by processing of bauxite aluminium is obtained from it. Some of the chief impurities present in the bauxite are iron oxide (Fe2O3) and silica (SiO2).
Question 23.Which two substances are added along with alumina to obtain aluminium from alumina by electrochemical reduction?
Answer:To obtain the alumina from aluminium by electrochemical reduction in which alumina has high melting point to bring down its melting point feldspar (CaF2) is added and cryolite (Na3AlF6) is added to increase the electrical conductivity so that electrolysis could be carried out easily.
Question 24.Which substance is called slag?
Answer:It is the waste material separated from metals during smelting or refining of ore.
e.g. when Calcium silicate (CaSiO3) formed as a result of the reaction of calcium oxide and silica in the blast furnace.
Question 25.Mention use of slag.
Answer:liquid cooled slag is used in construction of roads; it is used in concrete in combination with Portland cement.
Question 26.Which general principle is taken into consideration in determination of activity series of metals?
Answer:The general principle that is taken into consideration in determination of activity series is “A less active metal can be displaced from the solution of its salt by a more active metal”.
Question 27.Mention names of two softer metals.
Answer:In periodic table the elements present in group 1 i.e. alkali metals are soft and are easy to cut.
Two soft metals are:
Sodium (Na) and Potassium (K)
Question 28.Write names of two metals which are bad conductors of electricity.
Answer:Metals are generally good conductors of electricity but there are 2 metals which are exception and they are:
Lead (Pb) and Mercury (Hg)
Question 29.Write names of two metals oxides which form alkali by dissolving in water.
Answer:Generally metal oxides are basic in nature. So two metal oxides that are alkali by dissolving in water are:
i) Sodium oxide (Na2O)
ii) Potassium oxide (K2O)
Question 30.Which two metals burn with explosion in reaction with water?
Answer:Alkali metals burn with explosion in reaction with water and the 2 metals are:
i) Sodium
ii) Potassium
These metals react vigorously with water. The dihydrogen gas produced by these metals is so high that it explodes in water and burns speedily.
Question 31.Which two metals are generally not corroded?
Answer:The metals which are generally inert in nature do not corrode. Two examples are:
i) Gold
ii) Platinum
Question 32.Stainless steel is a homogeneous mixture of which three metals?
Answer:Stainless steel is an alloy which is hard and strong and does not gets easily corroded. It is mainly mixture 3 metals they are:
i) Iron
ii) Nickel
iii) Chromium
Question 33.Write chemical formula of rust.
Answer:Rust is a reddish coating when iron is attacked by moist air. The chemical formula of rust is Fe2O3.xH2O.
Question 34.Mention the formulas, names and physical states of the products in the following reactions:
(i) 2PbS(s) + 3O2(g)
(ii) MgCO3(s) 
(iii) Fe2O3(s) + 3CO(g) 
(iv) Fe2O3(s) + 2AI(s)
(v) 2AI(OH)3(s) 
(vi) CaO(s) + SiO2(s)
(vii) K2O(s) + H2O(I)
(viii) Mg(s) + 2H2O(I)
(ix) Zn(s) + 2HCI(aq)
(x) Ca(s) + CI2(g)
Answer:i. 2PbS(s) + 302(g) 2PbO(s) + SO2(g)
PbO = Lead oxide
SO2 = Sulphur dioxide
ii. MgCO3(s) 
MgO(s) + CO2 (g)
MgO = Magnesium oxide
CO2 = Carbon dioxide
iii. Fe2O3(s) + 3CO (g)
2Fe(s) + 3CO2 (g)
Fe = Iron
CO2 = Carbon dioxide
iv. Fe2O3(s) + 2Al(s) 2Fe(l) + Al2O3(s)
Fe = Iron
Al2O3 = Alumina
v. 2Al(OH)3(s) 
Al2O3(s) + 3H2O(g)
Al2O3 = Alumina
H2O = Water
vi. CaO(s) + SiO2(s) CaSiO3 (l)
CaSiO3 = Calcium silicate
vii. K2O(s) + H2O (l) 2KOH (aq)
2KOH = Potassium hydroxide
vii. Mg(s) + 2H2O (l) Mg(OH)2(aq) + H2 (g)
Mg(OH)2 = Magnesium hydroxide
H2 = Hydrogen
ix. Zn(s) + 2HCl (aq)ZnCl2 (aq) + H2 (g)
ZnCl2 = Zinc chloride
H2 = Hydrogen
x. Ca(s) + Cl2 (g) CaCl2(s)
CaCl2 = Calcium chloride
Question 35.Describe the method to remove impurity of iron from ore.
Answer:To remove impurity from iron ore the method of magnetic separation is used. Powdered ore is allowed to fall on the belt.
A magnet at one end of the belt which attracts the iron particles and fall nearer, the remaining particles fall away because of not being attracted.
Thus, by method of magnetic separation impurity of iron is removed from the ore.
Question 36.Explain the method of concentration of copper pyrites – the ore of copper.
Answer:Copper pyrite (Cu2S) is the ore of copper in the sulphide form so here method of froth-floatation should be used for concentration.
In this method, the fine powder of ore and water are filled in a big vessel and pine or turpentine oil is added to it. The sulphide particles of metals get wet and stick to it, while impurities do not get wet.
In this liquid mixture, air is passed with pressure through a tube. Hence, froth is produced around the light particles of the sulphide ore and comes to the surface of the liquid mixture.
The impurities get wet by water and settles down and the ore is removed with sieves and washed with water.
By this method clay, sand, etc are removed.
Question 37.Explain the refining of copper by electrolysis.
Answer:For refining of copper by electrolysis, impure copper rod is arranged as anode and rod of pure copper as cathode.
The aqueous solution of copper sulphate is taken as electrolyte.
When electric current is passed through the electrolyte the proportion of which copper from anode is dissolved in aqueous solution of copper sulphate and the same amount of copper from electrolyte is deposited on cathode.
Copper deposited on cathode is of 100% purity.
Question 38.Write four physical properties of metals.
Answer:Four physical properties of the metals are:
i) The surface of metals is shiny and can be polished.
ii) Generally, metals are in solid form and heavy in weight but metals like mercury and gallium exist in liquid form.
iii) Metals are good conductors of heat and electricity except metals such as lead and mercury.
iv) Some of the metals are malleable and ductile. E.g. gold, etc.
Question 39.Mention the components and uses off brass and bronze.
Answer:Both brass and bronze are alloy.
Brass: The components of brass are Copper (Cu) and Zinc (Zn).
The uses of brass are in preparing cooking utensils, machinery parts and musical instruments.
Bronze: The components of bronze are Copper (Cu) and Tin (Sn).
The uses of bronze are in making statues, coins and medals.
Question 40.Write a short note: Earth – Treasure of elements.
Answer:Earth is a treasure of elements as different elements are obtained directly or indirectly from:
i) Lithosphere: It is the part of the earth formed of sand, clay and stone, in which metal elements like aluminium, copper, iron, calcium, sodium, zinc etc. are in the forms of oxide, sulphide or carbonate.
ii) Hydrosphere: It is the mostly liquid part of the earth water of seas, rivers, lakes and the ice of polar region. In this part of region non-metals such as chlorine, fluorine and metals like sodium, potassium, calcium, etc. are found in combined forms.
iii) Atmosphere: The cover of gases around the earth is called atmosphere. Non-metallic gases such as nitrogen, oxygen, carbon dioxide, etc. are present.
Question 41.Explain different methods of concentration of ores.
Answer:There are mainly three different methods for concentration of ores and they are:
i) Concentration or centrifugation on the basis of difference of densities: This method is used when there is large difference in densities of ores and impurities. In this method finely, powdered ore is placed on a moving table with slots and it is moved rapidly so that light particles of metal remain in the slot in the table
ii) Froth floatation method: This method is used for the concentration of ores of the metals whose ores are in sulphide form.
The fine powder of ore and water are filled in a big vessel and pine or turpentine oil is added to it. The sulphide particles of metals get wet and stick to it, while impurities do not get wet.
Air is passed with pressure through a tube and froth is produced around the light particles of the sulphide ore and comes to the surface of the liquid mixture.
The impurities get wet by water and settles down and the ore is removed with sieves and washed with water.
By this method clay, sand, etc are removed.
iii) Magnetic separation: This method is used when either of ore or the impurity have some magnetic properties.
Powdered ore is allowed to fall on a belt.
A magnet at one end of the belt which attracts the ore particles and fall nearer, the remaining particles fall away because of not being attracted.
Thus, by method of magnetic separation impurities are removed from the ore.
Question 42.Explain roasting, calcinations and smelting.
Answer:These are the methods which are used to convert ore into metal oxides.
i) Roasting: When sulphide containing ore is heated for a long time in presence of excess of air to form metal oxide, this method of converting sulphide containing ore into metal oxide in presence of excess of air is called roasting.
e.g. 
ii) Calcination: When carbonate containing ore is heated for a long time in absence of air it is converted into metal oxide. This method of converting carbonate containing ore into metal oxide is called calcination.
e.g. 
iii) Smelting: If the ore is in melted form then it is called smelting.
Question 43.Explain chemical reduction and electrochemical reduction.
Answer:Reduction is the process in which metal oxides are converted into their respective metals.
There are 2 methods of reduction and they are:
i) Chemical reduction: This is the type of reduction in which metal oxide is heated with carbon or carbon monoxide to obtain the metal.
e.g. MnO2(s) + 2C(s) → Mn(s) + 2CO(g)
Fe2O3(s) + 3CO (g) → 2Fe(s) + 3CO2 (g)
Oxides of metals such as chromium, iron and manganese are heated with aluminium powder to obtain the metal.
e.g. 
ii) Electrochemical reduction: All metals cannot be reduced by chemical method, some metals such as sodium, magnesium, etc cannot be reduced from carbon because of their more attraction towards oxygen. Hence, electrochemical reduction is used for the reduction of active metals.
In electrochemical reduction electrodes of inert metals like graphite or platinum are used in electrochemical cell.
e.g. electrochemical reduction of alumina to obtain aluminium.
Cathode: 2Al+3(l) +6e-→ 2Al (l)
Anode: 3O-2(l) → 3/2 O2 (g) +6e-
Question 44.Explain liquefaction and zone refining method for refining of metals.
Answer:Some metals after reduction still contain some impurities which is further removed by refining. Two of which methods are:
iv) Liquefaction: This method is used for the metals having low melting point such as lead, tin, etc.
In this method furnace having a slope is used and the temperature of the furnace is kept higher than the melting point of metal.
When the impure metal is passed on the slope, the metal in it get melted and collected in the vessel but the melting point of impurities is high so they remain on the slope in solid form.
v) Zone refining: This method is based on the principle of fractional distillation to get a very high level of purity. Refining of semi metals is done by this method. In this method we remove trace impurities which are generally more soluble in molten metal, their solubility decreases as the metal cools and impurities are separated in the form of crystals.
Question 45.Discuss the extraction of aluminium from bauxite.
Answer:Aluminium is the most abundant metal on Earth. It is extracted from bauxite (Al2O3.2H2O) in 2 steps (i) to obtain alumina from bauxite (ii) to obtain alumina metal from alumina.
i) To obtain alumina from bauxite
Bauxite contains impurities such as iron oxide and sand (silica) is also present. Alumina is obtained from bauxite by Bayer’s process, in this process bauxite powder is taken and concentrated (45%) sodium hydroxide solution is added and then heated in closed vessel at 433 K temperature and 5 to 6 bar pressure, by hours by doing this aluminium oxide present in bauxite is converted into sodium aluminate which is soluble in water.
Al2O3(s) + 2NaOH (aq) → 2NaAlO2 (aq) + H2O (l)
Iron oxide is insoluble in water so it is removed by filtration but silica form sodium silicate which is soluble in water. Now, sodium aluminate and sodium silicate are there as filtrate. Excess of water is added and continuously stirred so that hydrolysis of sodium aluminate takes place and forms aluminium hydroxide and sodium silicate remains as impurity.
2NaAlO2 + 2H2O → Al(OH)3 + NaOH
The precipitate is washed repeatedly with water, dried and on heating at 1473 K temperature pure aluminium oxide (alumina) is obtained.
ii) To obtain aluminium from alumina
To obtain aluminium from alumina is done by electrochemical reduction and also known as Hall-Heroult method. In this process cryolite (Na3AlF6) is added so that electrolysis could be done easily and this mixture also works as good electric conductor, further the melting point is also brought down by addition of feldspar(CaF2).
The mixture of alumina, feldspar and cryolite is electrolysed in a vessel of iron having inner surface layered with carbon. In this the rods of carbon are joined by copper clamp which acts as anode and carbon layered graphite acts as cathode. When electric current is passed molten aluminium is deposited on cathode and dioxygen gas is produced at cathode. The molten aluminium is collected at the bottom of the cell is taken out.
Cathode: 2Al+3 + 6e-→ 2Al
Anode: 3O-2→ 3/2 O2 6e-
The dioxygen gas produced at anode reacts with the rod of carbon and forms carbon dioxide, as a result anode gets corroded and should be frequently replaced.
Question 46.Explain extraction of iron from haematite.
Answer:Iron is extracted from haematite by reduction in blast furnace.
The blast furnace is narrow in upper part, wide in middle and narrow at bottom part. The inner side of blast furnace has brick which are fire proof.
Most of the impurities present in ore are removed and then the concentrated ore is added to blast furnace with the help of hooper.
Due to the high temperature following reactions takes place and molten iron is obtained.
i) Coke combines with oxygen and forms carbon dioxide, due to exothermic reaction the temp of furnace becomes 1773K to 1993 K.
C(s) + O2(g) → CO2(g) + Heat
ii) Calcium oxide and carbon dioxide are formed due to decomposition of lime stone due to high temperature.
CaCO3(s) → CaO(s) + CO2
iii) When hot carbon dioxide goes up in the furnace it combines with coke and forms carbon monoxide, due to the endothermic reaction temperature comes down.
CO2 (s) + C(s) → CO(g)
iv) When the temp. of furnace is 673K to 973K, the iron oxide present in haematite is reduced to liquid form.
3Fe2O3 + CO → 2Fe3O4 + CO2
Fe3O4 + CO → 3FeO + CO2
FeO + CO → Fe + CO2
Calcium oxide formed during the reaction combines with impurity silica present in haematite and forms calcium silicate i.e. slag.
CaO + SiO2→ CaSiO3
Slag is lighter than iron so it floats and separated afterwards.
Question 47.Write the activity series of metals. Discuss the experiment for determination of activity series of Fe, Cu and Ag metals.
Answer:The activity series of metals is a list of metals ranked in order of decreasing reactivity to displace hydrogen gas from its aqueous solution. It can also be used to predict which metals will displace other metals in aqueous solutions.
Experiment:
Step-1: Take 2 test tubes and mark them as 1 and 2.
Step-2: In test tube 1 add 0.1 gram of copper sulphate and in test tube 2 add 0.1 gram of silver nitrate.
Step-3: Add 10 ml of water in both the test tubes and dissolve them.
Step-4: Now bring an iron nail and copper wire and add these to test tube 1 and 2.
Step-5: Place them in order and observe them.
Step-6: After 30 minutes we will observe that in test tube-1 iron nail will appear brown due to deposition of copper on it. In test tube -2 a white shining colour deposited on the copper wire.
Step-7: From the experiment we can conclude that iron (Fe) is more active metal than copper (Cu) because Cu from solution of CuSo4 was displaced by iron i.e. Fe>Cu. Cu is more active metal than Ag because Ag was displaced from its solution of AgNO3 by Cu metal i.e. Cu>Ag.
Thus the final order is Fe>Cu>Ag.
Activity series of metals:
K>Na>Ca>Mg>Al>Zn>Fe>Pb>[H]>Cu>Hg>Ag>Au
Question 48.Discuss chemical properties of metals.
Answer:Chemical properties of metals are:
i) Reaction with dioxygen: Metal elements can easily donate electrons to dioxygen atom.
Metal elements combine with oxygen to form oxides.
Metal + Dioxygen → Metal oxides
e.g. 2Mg(s) + O2(g) → 2MgO(s)
All metals do not react with dioxygen all metals show different properties such as metals like gold do not react with dioxygen at higher temperatures also.
ii) Reaction with water: Metals on reaction with water form hydroxides or oxides and produce dihydrogen gas. Metals such as sodium and potassium reacts vigorously with water and produce hydrogen gas.
Metal + Water → Metal hydroxide or Metal oxide + Dihydrogen gas
e.g. 2K(s) +2H2O(l) → 2KOH(aq) + H2(g)
Magnesium does not react with cold water but instead of it reacts with hot water to form magnesium hydroxide.
Mg(s) +2H2O (l) → MgOH (aq) + H2 (g)
Aluminium, zinc and iron metals do not reacts with hot or cold water but they react with water vapours to form oxides and hydrogen gas.
e.g. 2Al(s) +3H2O (l) → Al2O3 (aq) + 3H2 (g)
iii) Reaction with acid: All metals do not react with dilute acid. When metal reacts with dilute acid, salt of corresponding metal and di hydrogen gas is formed.
Metal + Dilute acid → Salt of corresponding metal + Dihydrogen gas
e.g. Mg(s) +H2SO4 (aq) → MgSO4 (aq) + H2 (g)
iv) Reaction with Dichlorine: Metals react with dichlorine to form metal chlorides.
Metal + Dichlorine gas → Metal chloride
e.g. Ca(s) + Cl2(g) → CaCl2(s)
v) Reaction with Dihydrogen: All metals do not react with dihydrogen because metals donate electrons and dihydrogen does not accept electron.
Metals such as Na, K, Ca combine with hydrogen and form hydrides of that metal.
Active metal + Dihydrogen gas → Metal hydride
e.g. Ca(s) + H2(g) → CaH2(s)
Question 49.Mentioning reasons for metallic corrosion describe the remedies to prevent it.
Answer:The erosion reaction of any metal with water or moisture when it comes in its contact is called metallic corrosion and due to continuous exposure to moist air or water is the reason for metallic corrosion.
Remedies to prevent corrosion:
•Applying paint
It is easy and cheap method to prevent corrosion of iron. The body of a car windows or pillars can be protected against corrosion but it is essential to apply paint at regular intervals.
•Applying oil
Applying oil to the mechanical tools such as hammer, gardener scissors, etc. could be a method for protection of iron from corrosion due to presence of oil layer.
•Galvanisation
It is another method for prevention of iron from corrosion in which very fine layer of zinc metal is coated on the surface of iron. If zinc is removed from the surface of iron, it does not get corroded because zinc is more active metal which spreads and prevents corrosion. It is an effective method of prevention.
•Certain suitable chemicals which are called inhibitors can also be used so that they combine with the surface of metal by chemical bond and prevent corrosion.
•By making alloys which makes them more harder and stronger and prevents corrosion for e.g. steel.
Question 50.What is an alloy? Mention its advantages. Mention the name of three alloys and also mention the components in them, properties and uses.
Answer:Alloys are the homogeneous mixture of 2 or more metals or metal and non-metals.
By making alloys there are changes in the properties of the element which is advantageous to us such as:
•It makes them hard and stronger. For e.g. steel (alloy of iron and carbon)
•Some of the alloys lowers the melting point which makes them easily fusible and this property is used in solders.
•Alloys of aluminium are light and stronger which are used in aeroplanes.
What is the chemical formula of alumina?
A. Al2O3
B. Al2O3. 2H2O
C. Al2O3.H2O
D. NaAlO2
Answer:
Alumina is the oxide of aluminium (aluminium oxide), which is produced from refining of bauxite.
Question 2.
Which of the following reactions is called roasting?
A. ZnCO3(s) ZnO(s) + CO2 (g)
B. 2ZnS(s) + 3022ZnO(s) + 2SO2 (g)
C. ZnO(s) + C(s) Zn(s) + CO (g)
D. Zn(s) + H2O (g) ZnO(s) + H2 (g)
Answer:
Roasting is the process in which sulphide(S-2) containing ore is heated in the presence of excess of air (O2) for a long time and it is converted into oxide.
So, in this question only in option (B) zinc sulphide (ZnS) reacts with the excess of oxygen to form zinc oxide (ZnO).
Question 3.
Which of the following is an alloy?
A. Silver
B. Gallium
C. 22 carat gold
D. 24 carat gold
Answer:
Alloy is a homogeneous mixture of 2 or more metals or metal and non-metal. In this question we will get the solution by options.
•In option (A) silver is a metal not a mixture and option
•(B) gallium is also metal and option
•(D) 24 carat gold is the pure form of gold but option
•(C) 22 carat gold is an alloy which consists of 22 parts of gold and 2 parts of other metals such as copper or silver. So, the correct option is (C).
Question 4.
During which reaction dihydrogen gas is not produced under normal conditions?
A. Metal + dilute sulphuric acid
B. Metal + dilute hydrochloric acid
C. Metal + dilute nitric acid
D. Metal + water
Answer:
Let us take all the options from start.
•In option (A) if metal reacts with sulphuric acid salt of corresponding acid and dihydrogen gas is formed and same thing happens for option (B) also.
•When metal reacts with nitric acid it does not produce dihydrogen gas instead of that oxide of nitrogen is formed because nitric acid is strong oxidising agent.
•So, the correct option is (C).
•In option (D) when metal reacts with water metal hydroxide or metal oxide and dihydrogen gas is formed.
Question 5.
In which of the following, displacement reaction is possible?
A. Solution of NaCl + coin of copper
B. Solution of MgCl2 + coin of aluminium
C. Solution of FeSO4 + coin of silver
D. Solution of AgNO3 + coin of copper
Answer:
According to the activity series copper is more active than silver so the displacement reaction in the (C) option. In other options the solution metal is more active so no displacement reaction can take place.
Question 6.
Which of the following is not possible?
A. Zn(s) + CuSO4 (aq) ZnSO4 (aq) + Cu(s)
B. Zn(s) + FeSO4 (aq) ZnSO4 (aq) + Fe(s)
C. Fe(s) + CuSO4 (aq) FeSO4 (aq) + Cu(s)
D. Cu(s) + FeSO4 (aq) CuSO4 (aq) + Fe(s)
Answer:
In the first three options the metals were more active than the solution so they could displace them but Cu is less active than Fe so it can’t displace it. So, the correct option is (D).
Question 7.
By which reaction metal is obtained from metal oxide?
A. Liquefaction
B. Reduction
C. Calcination
D. Roasting
Answer:
Reduction is the method in which pure metal is obtained from the metal oxide.
Question 8.
Which of the following statements is incorrect?
A. Corrosion of copper takes place by contact with air and water
B. The melting points and boiling points of metals are low.
C. The method to convert carbonate containing ore to metal oxide is called calcinations.
D. The displacement of less active metals from their solution takes place by more active metal.
Answer:
If we check option by option then we can clearly see that in option (B) it is mentioned that metals have low melting and boiling points but it is not true generally metals have high melting and boiling point. So, option (B) is correct.
Question 9.
Which alloy is used to solder the electric wires?
A. Copper + zinc
B. Aluminium + magnesium
C. Lead + tin
D. Copper + tin
Answer:
Melting point of alloy prepared from lead and tin is low so it is used to solder electric wires.
Question 10.
Which metal is available in highest proportion on the earth?
A. Iron
B. Copper
C. Aluminium
D. Silver
Answer:
Aluminium is the most abundant metal available on earth. It makes up to 8% of Earth’s crust by weight.
Question 11.
Which metal is used in thermometer?
A. Silver
B. Mercury
C. Sodium
D. Copper
Answer:
Mercury is liquid at room temperature and it is also sensitive to temperature so it is used in thermometer.
Question 12.
Which of the following substances is hygroscopic?
A. Cryolite
B. Feldspar
C. Anhydrous calcium chloride
D. Slag
Answer:
Hygroscopic is a substance which absorbs moisture from air. Anhydrous calcium chloride is highly hygroscopic that is the reason it is kept in tightly sealed container.
Question 13.
In which three sections elements are classified?
Answer:
All the elements are classified into 3 sections they are:
Metals, Non-metals and semi metals (metalloids).
Metals: A metal is a material that is hard, opaque, shiny, and has good electrical and thermal conductivity. Metals are generally malleable and ductile.
Non-metals: Non-metals have low melting and boiling points, densities, brittle if solid, and are usually poor conductors of heat and electricity.
Metalloids: A metalloid is an element that exhibits some properties of metals and some of non-metals.
Question 14.
Which metals are available in free state in nature?
Answer:
Gold and platinum ate the metals available in free state because of their very low activity.
Question 15.
In which form ores are available in nature?
Answer:
If in a certain mineral metal proportion is more and its extraction is advantageous then it is called ore. Ores are found in combined form in nature such as silicate, carbonate, oxide, phosphate, sulphide, etc.
Question 16.
Write names and formulas of two ores of iron.
Answer:
The main 2 ores of iron are Haematite its formula is Fe2O3 and Magnetite its formula is Fe3O4. These ores are mainly found in the region of Madhya Pradesh, Tamil Nadu, Orissa, etc.
Question 17.
Write names and formulas of two ores of copper.
Answer:
The 2 ores of copper are Cuprite (Cu2O) and Copper Glance (Cu2S). These ores are mainly found in the region of Rajasthan and Bihar.
Question 18.
Write names of the three methods for concentration of ores.
Answer:
Three methods of concentration of ores are:
(i) Concentration or centrifugation on the basis of difference of densities: This method is used when there is large difference in densities of ores and impurities.
(ii) Froth floatation method: This method is used for the concentration of ores of the metals whose ores are in sulphide form.
(iii) Magnetic separation: This method is used when either of ore or the impurity have some magnetic properties.
Question 19.
Which two methods are used for reduction of metal oxides?
Answer:
Reduction is carried out to obtain metal from metal oxide.
The 2 methods used to reduce metal oxide are:
i) Chemical reduction: When metal oxide is heated in blast furnace with carbon or carbon monoxide, metal is obtained.
e.g.
ii) Electrochemical reduction: Oxides of active metals such as sodium, magnesium, etc cannot be reduced from carbon because of their more attraction towards oxygen. Hence, electrochemical reduction is used for the reduction of active metals.
e.g. electrochemical reduction of alumina to obtain aluminium.
Question 20.
Write names of three methods used for refining of metals.
Answer:
The method to obtain about 100% pure metal by removing impurities in very small amounts in metal is called refining.
The three methods used for refining of metals are:
i) Electrolysis: In this method the rod of impure metal is taken as anode and rod of pure metal as cathode. The aqueous solution of salt of metal acts as electrolyte, when current is passed anode dissolves in electrolyte and the same amount of metal is deposited on cathode.
ii) Liquefaction: In this method furnace having a slope is used and the temperature of the furnace is kept higher than the melting point of metal.
When the impure metal is passed on the slope, the metal in it get melted and collected in the vessel but the melting point of impurities is high so they remain on the slope in solid form.
iii) Zone refining: In this method we remove trace impurities which are generally more soluble in molten metal, their solubility decreases as the metal cools and impurities are separated in the form of crystals.
Question 21.
What has been taken as anode and cathode for refining of metals in electrolysis method?
Answer:
In the method of electrolysis the rod of impure metal is taken as anode and rod of pure metal is taken as cathode. The aqueous solution of salt of, metal is used as an electrolyte. On passing electric current the anode dissolves in the electrolyte and the same proportion of pure metal gets deposited on cathode.
Refining of copper by electrolysis
Question 22.
Which chief impurities are present in bauxite?
Answer:
Bauxite is the ore of the aluminium by processing of bauxite aluminium is obtained from it. Some of the chief impurities present in the bauxite are iron oxide (Fe2O3) and silica (SiO2).
Question 23.
Which two substances are added along with alumina to obtain aluminium from alumina by electrochemical reduction?
Answer:
To obtain the alumina from aluminium by electrochemical reduction in which alumina has high melting point to bring down its melting point feldspar (CaF2) is added and cryolite (Na3AlF6) is added to increase the electrical conductivity so that electrolysis could be carried out easily.
Question 24.
Which substance is called slag?
Answer:
It is the waste material separated from metals during smelting or refining of ore.
e.g. when Calcium silicate (CaSiO3) formed as a result of the reaction of calcium oxide and silica in the blast furnace.
Question 25.
Mention use of slag.
Answer:
liquid cooled slag is used in construction of roads; it is used in concrete in combination with Portland cement.
Question 26.
Which general principle is taken into consideration in determination of activity series of metals?
Answer:
The general principle that is taken into consideration in determination of activity series is “A less active metal can be displaced from the solution of its salt by a more active metal”.
Question 27.
Mention names of two softer metals.
Answer:
In periodic table the elements present in group 1 i.e. alkali metals are soft and are easy to cut.
Two soft metals are:
Sodium (Na) and Potassium (K)
Question 28.
Write names of two metals which are bad conductors of electricity.
Answer:
Metals are generally good conductors of electricity but there are 2 metals which are exception and they are:
Lead (Pb) and Mercury (Hg)
Question 29.
Write names of two metals oxides which form alkali by dissolving in water.
Answer:
Generally metal oxides are basic in nature. So two metal oxides that are alkali by dissolving in water are:
i) Sodium oxide (Na2O)
ii) Potassium oxide (K2O)
Question 30.
Which two metals burn with explosion in reaction with water?
Answer:
Alkali metals burn with explosion in reaction with water and the 2 metals are:
i) Sodium
ii) Potassium
These metals react vigorously with water. The dihydrogen gas produced by these metals is so high that it explodes in water and burns speedily.
Question 31.
Which two metals are generally not corroded?
Answer:
The metals which are generally inert in nature do not corrode. Two examples are:
i) Gold
ii) Platinum
Question 32.
Stainless steel is a homogeneous mixture of which three metals?
Answer:
Stainless steel is an alloy which is hard and strong and does not gets easily corroded. It is mainly mixture 3 metals they are:
i) Iron
ii) Nickel
iii) Chromium
Question 33.
Write chemical formula of rust.
Answer:
Rust is a reddish coating when iron is attacked by moist air. The chemical formula of rust is Fe2O3.xH2O.
Question 34.
Mention the formulas, names and physical states of the products in the following reactions:
(i) 2PbS(s) + 3O2(g)
(ii) MgCO3(s)
(iii) Fe2O3(s) + 3CO(g)
(iv) Fe2O3(s) + 2AI(s)
(v) 2AI(OH)3(s)
(vi) CaO(s) + SiO2(s)
(vii) K2O(s) + H2O(I)
(viii) Mg(s) + 2H2O(I)
(ix) Zn(s) + 2HCI(aq)
(x) Ca(s) + CI2(g)
Answer:
i. 2PbS(s) + 302(g) 2PbO(s) + SO2(g)
PbO = Lead oxide
SO2 = Sulphur dioxide
ii. MgCO3(s) MgO(s) + CO2 (g)
MgO = Magnesium oxide
CO2 = Carbon dioxide
iii. Fe2O3(s) + 3CO (g) 2Fe(s) + 3CO2 (g)
Fe = Iron
CO2 = Carbon dioxide
iv. Fe2O3(s) + 2Al(s) 2Fe(l) + Al2O3(s)
Fe = Iron
Al2O3 = Alumina
v. 2Al(OH)3(s) Al2O3(s) + 3H2O(g)
Al2O3 = Alumina
H2O = Water
vi. CaO(s) + SiO2(s) CaSiO3 (l)
CaSiO3 = Calcium silicate
vii. K2O(s) + H2O (l) 2KOH (aq)
2KOH = Potassium hydroxide
vii. Mg(s) + 2H2O (l) Mg(OH)2(aq) + H2 (g)
Mg(OH)2 = Magnesium hydroxide
H2 = Hydrogen
ix. Zn(s) + 2HCl (aq)ZnCl2 (aq) + H2 (g)
ZnCl2 = Zinc chloride
H2 = Hydrogen
x. Ca(s) + Cl2 (g) CaCl2(s)
CaCl2 = Calcium chloride
Question 35.
Describe the method to remove impurity of iron from ore.
Answer:
To remove impurity from iron ore the method of magnetic separation is used. Powdered ore is allowed to fall on the belt.
A magnet at one end of the belt which attracts the iron particles and fall nearer, the remaining particles fall away because of not being attracted.
Thus, by method of magnetic separation impurity of iron is removed from the ore.
Question 36.
Explain the method of concentration of copper pyrites – the ore of copper.
Answer:
Copper pyrite (Cu2S) is the ore of copper in the sulphide form so here method of froth-floatation should be used for concentration.
In this method, the fine powder of ore and water are filled in a big vessel and pine or turpentine oil is added to it. The sulphide particles of metals get wet and stick to it, while impurities do not get wet.
In this liquid mixture, air is passed with pressure through a tube. Hence, froth is produced around the light particles of the sulphide ore and comes to the surface of the liquid mixture.
The impurities get wet by water and settles down and the ore is removed with sieves and washed with water.
By this method clay, sand, etc are removed.
Question 37.
Explain the refining of copper by electrolysis.
Answer:
For refining of copper by electrolysis, impure copper rod is arranged as anode and rod of pure copper as cathode.
The aqueous solution of copper sulphate is taken as electrolyte.
When electric current is passed through the electrolyte the proportion of which copper from anode is dissolved in aqueous solution of copper sulphate and the same amount of copper from electrolyte is deposited on cathode.
Copper deposited on cathode is of 100% purity.
Question 38.
Write four physical properties of metals.
Answer:
Four physical properties of the metals are:
i) The surface of metals is shiny and can be polished.
ii) Generally, metals are in solid form and heavy in weight but metals like mercury and gallium exist in liquid form.
iii) Metals are good conductors of heat and electricity except metals such as lead and mercury.
iv) Some of the metals are malleable and ductile. E.g. gold, etc.
Question 39.
Mention the components and uses off brass and bronze.
Answer:
Both brass and bronze are alloy.
Brass: The components of brass are Copper (Cu) and Zinc (Zn).
The uses of brass are in preparing cooking utensils, machinery parts and musical instruments.
Bronze: The components of bronze are Copper (Cu) and Tin (Sn).
The uses of bronze are in making statues, coins and medals.
Question 40.
Write a short note: Earth – Treasure of elements.
Answer:
Earth is a treasure of elements as different elements are obtained directly or indirectly from:
i) Lithosphere: It is the part of the earth formed of sand, clay and stone, in which metal elements like aluminium, copper, iron, calcium, sodium, zinc etc. are in the forms of oxide, sulphide or carbonate.
ii) Hydrosphere: It is the mostly liquid part of the earth water of seas, rivers, lakes and the ice of polar region. In this part of region non-metals such as chlorine, fluorine and metals like sodium, potassium, calcium, etc. are found in combined forms.
iii) Atmosphere: The cover of gases around the earth is called atmosphere. Non-metallic gases such as nitrogen, oxygen, carbon dioxide, etc. are present.
Question 41.
Explain different methods of concentration of ores.
Answer:
There are mainly three different methods for concentration of ores and they are:
i) Concentration or centrifugation on the basis of difference of densities: This method is used when there is large difference in densities of ores and impurities. In this method finely, powdered ore is placed on a moving table with slots and it is moved rapidly so that light particles of metal remain in the slot in the table
ii) Froth floatation method: This method is used for the concentration of ores of the metals whose ores are in sulphide form.
The fine powder of ore and water are filled in a big vessel and pine or turpentine oil is added to it. The sulphide particles of metals get wet and stick to it, while impurities do not get wet.
Air is passed with pressure through a tube and froth is produced around the light particles of the sulphide ore and comes to the surface of the liquid mixture.
The impurities get wet by water and settles down and the ore is removed with sieves and washed with water.
By this method clay, sand, etc are removed.
iii) Magnetic separation: This method is used when either of ore or the impurity have some magnetic properties.
Powdered ore is allowed to fall on a belt.
A magnet at one end of the belt which attracts the ore particles and fall nearer, the remaining particles fall away because of not being attracted.
Thus, by method of magnetic separation impurities are removed from the ore.
Question 42.
Explain roasting, calcinations and smelting.
Answer:
These are the methods which are used to convert ore into metal oxides.
i) Roasting: When sulphide containing ore is heated for a long time in presence of excess of air to form metal oxide, this method of converting sulphide containing ore into metal oxide in presence of excess of air is called roasting.
e.g.
ii) Calcination: When carbonate containing ore is heated for a long time in absence of air it is converted into metal oxide. This method of converting carbonate containing ore into metal oxide is called calcination.
e.g.
iii) Smelting: If the ore is in melted form then it is called smelting.
Question 43.
Explain chemical reduction and electrochemical reduction.
Answer:
Reduction is the process in which metal oxides are converted into their respective metals.
There are 2 methods of reduction and they are:
i) Chemical reduction: This is the type of reduction in which metal oxide is heated with carbon or carbon monoxide to obtain the metal.
e.g. MnO2(s) + 2C(s) → Mn(s) + 2CO(g)
Fe2O3(s) + 3CO (g) → 2Fe(s) + 3CO2 (g)
Oxides of metals such as chromium, iron and manganese are heated with aluminium powder to obtain the metal.
e.g.
ii) Electrochemical reduction: All metals cannot be reduced by chemical method, some metals such as sodium, magnesium, etc cannot be reduced from carbon because of their more attraction towards oxygen. Hence, electrochemical reduction is used for the reduction of active metals.
In electrochemical reduction electrodes of inert metals like graphite or platinum are used in electrochemical cell.
e.g. electrochemical reduction of alumina to obtain aluminium.
Cathode: 2Al+3(l) +6e-→ 2Al (l)
Anode: 3O-2(l) → 3/2 O2 (g) +6e-
Question 44.
Explain liquefaction and zone refining method for refining of metals.
Answer:
Some metals after reduction still contain some impurities which is further removed by refining. Two of which methods are:
iv) Liquefaction: This method is used for the metals having low melting point such as lead, tin, etc.
In this method furnace having a slope is used and the temperature of the furnace is kept higher than the melting point of metal.
When the impure metal is passed on the slope, the metal in it get melted and collected in the vessel but the melting point of impurities is high so they remain on the slope in solid form.
v) Zone refining: This method is based on the principle of fractional distillation to get a very high level of purity. Refining of semi metals is done by this method. In this method we remove trace impurities which are generally more soluble in molten metal, their solubility decreases as the metal cools and impurities are separated in the form of crystals.
Question 45.
Discuss the extraction of aluminium from bauxite.
Answer:
Aluminium is the most abundant metal on Earth. It is extracted from bauxite (Al2O3.2H2O) in 2 steps (i) to obtain alumina from bauxite (ii) to obtain alumina metal from alumina.
i) To obtain alumina from bauxite
Bauxite contains impurities such as iron oxide and sand (silica) is also present. Alumina is obtained from bauxite by Bayer’s process, in this process bauxite powder is taken and concentrated (45%) sodium hydroxide solution is added and then heated in closed vessel at 433 K temperature and 5 to 6 bar pressure, by hours by doing this aluminium oxide present in bauxite is converted into sodium aluminate which is soluble in water.
Al2O3(s) + 2NaOH (aq) → 2NaAlO2 (aq) + H2O (l)
Iron oxide is insoluble in water so it is removed by filtration but silica form sodium silicate which is soluble in water. Now, sodium aluminate and sodium silicate are there as filtrate. Excess of water is added and continuously stirred so that hydrolysis of sodium aluminate takes place and forms aluminium hydroxide and sodium silicate remains as impurity.
2NaAlO2 + 2H2O → Al(OH)3 + NaOH
The precipitate is washed repeatedly with water, dried and on heating at 1473 K temperature pure aluminium oxide (alumina) is obtained.
ii) To obtain aluminium from alumina
To obtain aluminium from alumina is done by electrochemical reduction and also known as Hall-Heroult method. In this process cryolite (Na3AlF6) is added so that electrolysis could be done easily and this mixture also works as good electric conductor, further the melting point is also brought down by addition of feldspar(CaF2).
The mixture of alumina, feldspar and cryolite is electrolysed in a vessel of iron having inner surface layered with carbon. In this the rods of carbon are joined by copper clamp which acts as anode and carbon layered graphite acts as cathode. When electric current is passed molten aluminium is deposited on cathode and dioxygen gas is produced at cathode. The molten aluminium is collected at the bottom of the cell is taken out.
Cathode: 2Al+3 + 6e-→ 2Al
Anode: 3O-2→ 3/2 O2 6e-
The dioxygen gas produced at anode reacts with the rod of carbon and forms carbon dioxide, as a result anode gets corroded and should be frequently replaced.
Question 46.
Explain extraction of iron from haematite.
Answer:
Iron is extracted from haematite by reduction in blast furnace.
The blast furnace is narrow in upper part, wide in middle and narrow at bottom part. The inner side of blast furnace has brick which are fire proof.
Most of the impurities present in ore are removed and then the concentrated ore is added to blast furnace with the help of hooper.
Due to the high temperature following reactions takes place and molten iron is obtained.
i) Coke combines with oxygen and forms carbon dioxide, due to exothermic reaction the temp of furnace becomes 1773K to 1993 K.
C(s) + O2(g) → CO2(g) + Heat
ii) Calcium oxide and carbon dioxide are formed due to decomposition of lime stone due to high temperature.
CaCO3(s) → CaO(s) + CO2
iii) When hot carbon dioxide goes up in the furnace it combines with coke and forms carbon monoxide, due to the endothermic reaction temperature comes down.
CO2 (s) + C(s) → CO(g)
iv) When the temp. of furnace is 673K to 973K, the iron oxide present in haematite is reduced to liquid form.
3Fe2O3 + CO → 2Fe3O4 + CO2
Fe3O4 + CO → 3FeO + CO2
FeO + CO → Fe + CO2
Calcium oxide formed during the reaction combines with impurity silica present in haematite and forms calcium silicate i.e. slag.
CaO + SiO2→ CaSiO3
Slag is lighter than iron so it floats and separated afterwards.
Question 47.
Write the activity series of metals. Discuss the experiment for determination of activity series of Fe, Cu and Ag metals.
Answer:
The activity series of metals is a list of metals ranked in order of decreasing reactivity to displace hydrogen gas from its aqueous solution. It can also be used to predict which metals will displace other metals in aqueous solutions.
Experiment:
Step-1: Take 2 test tubes and mark them as 1 and 2.
Step-2: In test tube 1 add 0.1 gram of copper sulphate and in test tube 2 add 0.1 gram of silver nitrate.
Step-3: Add 10 ml of water in both the test tubes and dissolve them.
Step-4: Now bring an iron nail and copper wire and add these to test tube 1 and 2.
Step-5: Place them in order and observe them.
Step-6: After 30 minutes we will observe that in test tube-1 iron nail will appear brown due to deposition of copper on it. In test tube -2 a white shining colour deposited on the copper wire.
Step-7: From the experiment we can conclude that iron (Fe) is more active metal than copper (Cu) because Cu from solution of CuSo4 was displaced by iron i.e. Fe>Cu. Cu is more active metal than Ag because Ag was displaced from its solution of AgNO3 by Cu metal i.e. Cu>Ag.
Thus the final order is Fe>Cu>Ag.
Activity series of metals:
K>Na>Ca>Mg>Al>Zn>Fe>Pb>[H]>Cu>Hg>Ag>Au
Question 48.
Discuss chemical properties of metals.
Answer:
Chemical properties of metals are:
i) Reaction with dioxygen: Metal elements can easily donate electrons to dioxygen atom.
Metal elements combine with oxygen to form oxides.
Metal + Dioxygen → Metal oxides
e.g. 2Mg(s) + O2(g) → 2MgO(s)
All metals do not react with dioxygen all metals show different properties such as metals like gold do not react with dioxygen at higher temperatures also.
ii) Reaction with water: Metals on reaction with water form hydroxides or oxides and produce dihydrogen gas. Metals such as sodium and potassium reacts vigorously with water and produce hydrogen gas.
Metal + Water → Metal hydroxide or Metal oxide + Dihydrogen gas
e.g. 2K(s) +2H2O(l) → 2KOH(aq) + H2(g)
Magnesium does not react with cold water but instead of it reacts with hot water to form magnesium hydroxide.
Mg(s) +2H2O (l) → MgOH (aq) + H2 (g)
Aluminium, zinc and iron metals do not reacts with hot or cold water but they react with water vapours to form oxides and hydrogen gas.
e.g. 2Al(s) +3H2O (l) → Al2O3 (aq) + 3H2 (g)
iii) Reaction with acid: All metals do not react with dilute acid. When metal reacts with dilute acid, salt of corresponding metal and di hydrogen gas is formed.
Metal + Dilute acid → Salt of corresponding metal + Dihydrogen gas
e.g. Mg(s) +H2SO4 (aq) → MgSO4 (aq) + H2 (g)
iv) Reaction with Dichlorine: Metals react with dichlorine to form metal chlorides.
Metal + Dichlorine gas → Metal chloride
e.g. Ca(s) + Cl2(g) → CaCl2(s)
v) Reaction with Dihydrogen: All metals do not react with dihydrogen because metals donate electrons and dihydrogen does not accept electron.
Metals such as Na, K, Ca combine with hydrogen and form hydrides of that metal.
Active metal + Dihydrogen gas → Metal hydride
e.g. Ca(s) + H2(g) → CaH2(s)
Question 49.
Mentioning reasons for metallic corrosion describe the remedies to prevent it.
Answer:
The erosion reaction of any metal with water or moisture when it comes in its contact is called metallic corrosion and due to continuous exposure to moist air or water is the reason for metallic corrosion.
Remedies to prevent corrosion:
•Applying paint
It is easy and cheap method to prevent corrosion of iron. The body of a car windows or pillars can be protected against corrosion but it is essential to apply paint at regular intervals.
•Applying oil
Applying oil to the mechanical tools such as hammer, gardener scissors, etc. could be a method for protection of iron from corrosion due to presence of oil layer.
•Galvanisation
It is another method for prevention of iron from corrosion in which very fine layer of zinc metal is coated on the surface of iron. If zinc is removed from the surface of iron, it does not get corroded because zinc is more active metal which spreads and prevents corrosion. It is an effective method of prevention.
•Certain suitable chemicals which are called inhibitors can also be used so that they combine with the surface of metal by chemical bond and prevent corrosion.
•By making alloys which makes them more harder and stronger and prevents corrosion for e.g. steel.
Question 50.
What is an alloy? Mention its advantages. Mention the name of three alloys and also mention the components in them, properties and uses.
Answer:
Alloys are the homogeneous mixture of 2 or more metals or metal and non-metals.
By making alloys there are changes in the properties of the element which is advantageous to us such as:
•It makes them hard and stronger. For e.g. steel (alloy of iron and carbon)
•Some of the alloys lowers the melting point which makes them easily fusible and this property is used in solders.
•Alloys of aluminium are light and stronger which are used in aeroplanes.