Ch. No. 8. Understanding Metals and Non – metals
Q1. Name the following:
1. Metal which forms an amphoteric oxide?
Ans. Aluminium.
2. An alloy of copper and zinc.
Ans. Brass
3. A compound which is added to lower the fusion temperature of an electrolytic bath in extraction of aluminium.
Ans. Cryolite.
4. A metal which does not react with cold water but reacts with steam.
Ans. Aluminium.
5. A common ore of aluminium.
Ans. Bauxite.
Q2. From the list of characteristic given below select the five which are relevant to metals and their compounds.
1. Ductile
2. Conduct electricity
3. Acidic oxide.
4. Discharged at anode basic oxides.
5. Brittle
6. (1,2,3) valence electrons.
7. Discharged at cathode.
8. (5,6,7) valence electrons.
9. Occurring in solid or gaseous state.
10. Basic oxides.
Ans. Characteristic of metals are:
1. Ductile
2. Conduct of electricity.
3. Basic oxides
4. (1,2,3) valence electrons.
5. Discharged at cathode.
Q3. Name one metal each occurring as,
1. A sulphide.
Ans. Copper
2. A carbonate
Ans. Zinc
3. An oxide
Ans. Aluminium
Q4. Explain the following terms.
1. Minerals: - The naturally occurring compounds of metals along with other impurities are known as minerals.
2. Gangue: - Ores contain metal compounds with some of the impurities like soil, sand, rocky material etc. These impurities are called as gangue.
3. Ores: -The minerals from which metals are extracted profitably and conveniently are called ores.
4. Metallurgy: - The process used for extraction of metals in their pure form from their ores is called metallurgy.
5. Roasting: - The sulphide ores are first converted into oxides by heating strongly in excess of air. This process is called as roasting.
Q5. Give scientific reasons for the following.
1. Sodium is stored under kerosene.
Ans.
i. Sodium is a highly reactive metal.
ii. Sodium reacts with oxygen in air at room temperature to form, sodium oxide.
iii. Therefore, it catches fire and starts burning when open in the air.
iv. Hence, sodium is stored under kerosene to prevent its reaction with oxygen, moisture and carbon dioxide.
2. Gold and silver are used to make jewellery.
Ans.
i. Gold and silver are highly inactive metals. Therefore, they do not undergo corrosion due to attack by moisture and atmospheric gases.
ii. Gold and Silver are very shiny metals (lustrous).
iii. They are used to make jewellery because of its bright shiny surface and high resistance to corrosion.
3. Calcium floats over water during the reaction with water.
Ans.
i. Calcium reacts with water less vigorously so that the heat evolved is not sufficient for the hydrogen formed, to catch fire.
ii. Instead, calcium starts floating because the bubbles of hydrogen gas formed stick to the surface of the water calcium.
4. Ionic compounds have high melting and boiling points
Ans.
i. Ionic compounds are solids and hard due to strong force of attraction between positive and negative ions in their molecules.
ii. A considerable amount of energy is required to break the strong inter molecular attraction.
iii. Hence ionic compounds have high melting and boiling points.
5. Tarnished copper utensils are cleaned with lime juice or tamarind.
Ans.
i. When copper utensils are exposed to moist air, they get tarnished or corroded due to the formation of green copper carbonate.
ii. When these tarnished vessels are rubbed with lime juice or tamarind the weak acids present in them dissolve the green copper carbonate and original shine returns.
Q6. Sudha dipped a copper coin in a solution of silver nitrate. After some time she saw the silver shine on the coin. Why? Give the balanced chemical equation for the same.
Ans.
1. Copper is more reactive than silver. Hence displacement reaction occurs.
2. When copper coin is dipped in silver nitrate solution forming copper nitrate and silver metal.
3. A shining white deposit of silver metal is formed on copper coin. Hence she saw a silver shine on the copper coin.
Balanced equation:-
2AgNO3(ag) + Cu(s) → Cu(NO3)2(ag) + 2Ag(s)
Q7. Metal A has electronic configuration of 2,8,1 and metal B has 2,8,8,2 which is more reactive. Identify these metals and vie their reactions with dil HCl.
Ans. Metal A is Sodium (Na) : 2,8,1
Metal B is Calcium (Ca) : 2,8,8,2.
Metal A (Sodium) is more reactive than metal B (Calcium).
Reaction: -
i. Sodium metal reacts violently with dilute hydrochloric acid to form sodium chlorides and hydrogen.
2Na(a) + 2HCl(aq) → 2NaCl(aq) + H2(g)
ii. Calcium reacts less vigorously to form calcium chloride and hydrogen.
Ca + 2HCl → CaCl2 + H2
Q8. To obtain (zinc) Zn from zinc sulphide two chemical reaction are involved
Write the equations for A and B.
Ans. Equation for A: Roasting is the process in which a sulphide ore is strongly heated in the presence of air to convert it into metal oxide.
Equation for B : Zinc metal is extracted by the reduction of its oxide with carbon (or coke). Thus, when, Zinc oxide is heated with carbon, Zinc metal is produced.
Q9. Translate the following statements into chemical equation and then balance them.
1. When steam is passed over aluminium.
Ans. Aluminium reacts with steam to form aluminium oxide and hydrogen gas.
2. Extraction of copper from its sulphide ore.
Ans.
i. The concentrated copper sulphide ore is roasted in air when a part of copper sulphide is oxidized to copper oxide.
ii. Copper oxide formed above reacts with the remaining copper sulphide to form copper metal and sulphur dioxide.
3. Thermit reaction.
Ans. Iron oxide reacts with aluminium to give iron and aluminium oxide evolving lot of heat.
4. When magnesium reacts with hot water.
Ans. Magnesium reacts with hot water to form magnesium hydroxide and hydrogen.
5. What happens when aluminium oxide dissolves in aqueous sodium hydroxide?
Ans. Aluminium oxide being amphoteric in nature dissolves in aqueous sodium hydroxide to form water soluble sodium aluminate.
Q10. In the extraction of aluminium
1. Name the process of concentration of Bauxite.
2. Write the cathode reaction in electrolytic reduction of alumina.
3. Write the function and formula of cryolite in the extraction of aluminium.
4. Write an equation for the action of heat on aluminium hydroxide.
5. Draw the diagram of extraction of aluminium.
6. Why is it necessary to replace anodes time to time?
7. What happens when aluminium ore is heated with concentrated caustic soda. Write the balanced chemical equation for the same.
Ans.
i. The process of concentration of Bauxite is done by Bayer’s Process.
ii. The positively charged aluminium ions (Al3+) are attracted to the cathode (negative electrode). The aluminium ions accept electrons from the cathode and get reduced to form aluminium atoms (or aluminium metal).
Cathode reaction :
iii. Alumina has a very high melting point (>20000C). Cryolite lowers the fusion temperature from 20000C to 10000C and enhances conductivity.
Chemical formula of cryolite:
iv. Equation:
v. Diagram
vi. As the anode gets oxidized during the electrolysis of alumina. It has to be replaced from time to time.
vii. When aluminium or is heated with caustic soda solution under high pressure for 2 to 8 hours at water soluble sodium aluminate is formed.
Q11. Write two methods of preventing rusting of iron.
Ans.
i. The most common method of preventing the rusting of iron is to coat its surface with paint or apply grease, oil or varnish.
ii. Rusting of iron can be prevented by galvanization. The process of depositing a thin layer of Zinc metal on Iron objects is called galvanization.
Q12. What is an alloy? Give two examples with their chemical composition.
Ans. An alloy is a homogenous mixture of two or more metals or a metal and a non – metal in definite proportion.
Eg.
i. Brass – copper and zinc.
ii. Stainless steel – iron, nickel and chromium.
Q13. Arrange the following metals in the decreasing order of chemical reactivity, Cu, Mg, Fe, Na, Ca, Zn.
Ans. The arrangement of metals in the decreasing order of their chemical reactivity are Na > Ca > Mg > Zn > Fe > Cu.
Q14. Explain the formation of an ionic compound between metal and a non – metal by transfer of electrons with Mg as the metal and Cl as a non – metal to illustrate your answer.
Ans. Magnesium is a metal whereas chlorine is a non – metal. Magnesium reacts with chlorine to form an ionic compound magnesium chloride.
The atomic number of magnesium is 12, so its electronic configuration is 2,8,2. It has 2 valance electrons. A magnesium atom donates its 2 valence electrons (to two chlorine atoms) and forms a stable magnesium ion,
The atomic number of chlorine is 17, and its electronic configuration is 2,8,7. Chlorine atom has 7 valance electrons, so it requires only 1 more electrons to complete its octet. Since, one magnesium atom donates 2 electrons, so, two chlorine atoms take these two electrons and form two chloride ions.
The positively charged magnesium ions and negatively charged chloride ions are held together by electrostatic force of attraction to form magnesium chloride compound.
Q15. An element x on reacting oxygen forms an oxide X2O. This oxide dissolves in water and turns red litmus blue. State whether element X is a metal or a non – metal. Explain with proper example.
Ans. The element X is very likely to be a non – metal because most of the oxides of non – metals are acidic and are soluble in water.