11
Read the following passage and answer the questions that follow :
When metals are burnt in air, they form oxides. Metal oxides are generally basic in nature. But some metal oxides show both acidic as well as basic behaviour. Most metal oxides are insoluble in water, but some of these dissolve in water to form alkalis. Different metals show different reactivities towards oxygen. Metals such as sodium and potassium react vigorously whereas metals like silver and gold do not react with oxygen even at high temperature.
(a) Why are metals like sodium and potassium kept immersed in kerosene oil ?
(b) Why does copper metal turn black on heating?
(c) (i) What are the amphoteric oxides ? Give two examples.
OR
(c) (ii) (I) Name a water soluble metal oxide. Write the chemical equation for its reaction with water.
(II) Why do silver and gold not react with oxygen even at high temperature ?
When metals are burnt in air, they form oxides. Metal oxides are generally basic in nature. But some metal oxides show both acidic as well as basic behaviour. Most metal oxides are insoluble in water, but some of these dissolve in water to form alkalis. Different metals show different reactivities towards oxygen. Metals such as sodium and potassium react vigorously whereas metals like silver and gold do not react with oxygen even at high temperature.
(a) Why are metals like sodium and potassium kept immersed in kerosene oil ?
(b) Why does copper metal turn black on heating?
(c) (i) What are the amphoteric oxides ? Give two examples.
OR
(c) (ii) (I) Name a water soluble metal oxide. Write the chemical equation for its reaction with water.
(II) Why do silver and gold not react with oxygen even at high temperature ?
Show SolutionHide Solution↓
(a)Because of their high reactivity they react vigorously with air and water and catch fire if kept in open. (1 Mark)
(b)Copper combines with oxygen to form $\ce{CuO}$ or Copper (II) Oxide, a black oxide/ $\ce{2Cu(s) + O2 -> 2CuO(s)}$ (1 Mark)
(c) (i) Oxides which react with both acid and base to produce salt and water/ metal oxide which shows both acidic as well as basic behaviour. (1 Mark)
Examples: $\ce{Al2O3}$, $\ce{ZnO}$ (½+½ Marks)
(c) (ii) (I) • $\ce{Na2O/K2O/CaO}$/Sodium oxide /Potassium oxide/Calcium oxide (½ Mark)
• $\ce{Na2O+H2O -> 2NaOH}$ / $\ce{K2O+H2O -> 2KOH}$ / $\ce{CaO+H2O -> Ca(OH)2}$ (1 Mark)
(II) Because of the least reactive nature of silver and gold. (½ Mark)
(b)Copper combines with oxygen to form $\ce{CuO}$ or Copper (II) Oxide, a black oxide/ $\ce{2Cu(s) + O2 -> 2CuO(s)}$ (1 Mark)
(c) (i) Oxides which react with both acid and base to produce salt and water/ metal oxide which shows both acidic as well as basic behaviour. (1 Mark)
Examples: $\ce{Al2O3}$, $\ce{ZnO}$ (½+½ Marks)
(c) (ii) (I) • $\ce{Na2O/K2O/CaO}$/Sodium oxide /Potassium oxide/Calcium oxide (½ Mark)
• $\ce{Na2O+H2O -> 2NaOH}$ / $\ce{K2O+H2O -> 2KOH}$ / $\ce{CaO+H2O -> Ca(OH)2}$ (1 Mark)
(II) Because of the least reactive nature of silver and gold. (½ Mark)