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Practice each question, then open the answer or worked solution.
Why is sodium kept immersed in kerosene oil?
Solution: Sodium is a reactive metal. If kept open it will react with oxygen to explore and catch fire. Sodium metal is kept immersed in kerosene to prevent their reaction with oxygen, moisture and carbon dioxide of air.
Write equations for the reactions of
(i) iron with steam
(ii) calcium and potassium with water
Solution: (i) Iron reacts with steam to form a magnetic oxide of Fe with the liberation of H2.
3Fe(s) + 4H2O(g) → Fe3O4(s) + 4H2(g)
(ii) Calcium reacts with water to form calcium hydroxide and hydrogen.
Ca(s) + 2H2O(I) → Ca(OH)2(aq) + H2(g)
Potassium reacts with cold water violently immediately with evolution of H2 which catches fire.
2K(s) + 2H2O(I) → 2KOH(aq) + 2H2(g)
Samples of four metals A, B, C and D were taken and added to the following solution one by one. The results obtained have been tabulated as follows
| Metal | Iron(II) sulphate | Copper(II) sulphate | Zinc sulphate | Silver Nitrate |
| A | No reaction | Displacement | – | – |
| B | Displacement | – | – | – |
| C | No reaction | No reaction | No reaction | Displacement |
| D | No reaction | No reaction | No reaction | No reaction |
Use the table above to answer the following questions about metals A, B, C and D.
(i) Metal B is the most reactive as it gives displacement reaction with iron (II) sulphate.
(ii) When metal B is added to copper (II) sulphate solution, a displacement reaction will take place because of which the blue colour of copper (II) sulphate solution will fade and a red-brown deposit of copper will be formed on metal B.
(iii)Metal B is the most reactive because it displaces iron from its salt solution. Metal A is less reactive because it displaces copper from its salt solution. Metal C is still less reactive because it can displace only silver from its salt solution, and metal D is the least reactive because it cannot displace any metal from its salt solution. Hence, the decreasing order of reactivity of the metals is B > A > C > D.
Which gas is produced when dilute hydrochloric acid is added to a reactive metal? Write the chemical reaction when iron reacts with dilute H2SO4.
Solution: Hydrogen gas is liberated when dilute HCl is added to a reactive metal.
Fe(s) + H2SO4(aq) → FeSO4(aq) + H2(g)
What would you observe when zinc is added to a solution of iron (II) sulphate? Write the chemical reaction that takes place.
Solution: Zinc is more reactive (more electro positive) than iron. Therefore, Zinc displaces Iron from its salt solution. The colour of ferrous sulphate is pale green, which turns colourless.
FeSO4 + Zn → ZnSO4 + Fe(s)
Light green Zinc sulphate(Colourless)