CBSE · Class 10 · Science · Metals and Non-metalsAnswer the following questions regarding the chemical properties of metals and non-metals: (a) What are amphoteric oxides? Give two examples of amphoteric oxides and write balanced chemical equations for their reactions with both acids and bases. (b) Explain how metals react with water. Compare the reactions of Sodium, Calcium, Magnesium, and Iron with water, providing balanced chemical equations for each.

(a) Amphoteric Oxides

Definition: Metal oxides that show both acidic as well as basic behavior are called amphoteric oxides. They react with both acids and bases to produce salt and water.

Examples and Chemical Reactions:

1. Aluminium Oxide ($\text{Al}_2\text{O}_3$):

   • Reaction with Acid (HCl): Shows basic character. $$\text{Al}_2\text{O}_3\text{ (s)} + 6\text{HCl (aq)} \rightarrow 2\text{AlCl}_3\text{ (aq)} + 3\text{H}_2\text{O (l)}$$
   • Reaction with Base (NaOH): Shows acidic character. $$\text{Al}_2\text{O}_3\text{ (s)} + 2\text{NaOH (aq)} \rightarrow 2\text{NaAlO}_2\text{ (aq) [Sodium aluminate]} + \text{H}_2\text{O (l)}$$

2. Zinc Oxide ($\text{ZnO}$):

   • Reaction with Acid (HCl): $$\text{ZnO (s)} + 2\text{HCl (aq)} \rightarrow \text{ZnCl}_2\text{ (aq)} + \text{H}_2\text{O (l)}$$
   • Reaction with Base (NaOH): $$\text{ZnO (s)} + 2\text{NaOH (aq)} \rightarrow \text{Na}_2\text{ZnO}_2\text{ (aq) [Sodium zincate]} + \text{H}_2\text{O (l)}$$

(b) Reaction of Metals with Water

\nMetals react with water to form metal oxide or metal hydroxide along with the evolution of hydrogen gas. However, different metals show varying reactivities toward water:

1. Sodium (Highly Reactive - Cold Water):

   • Reacts violently and vigorously with cold water. The reaction is highly exothermic, and evolved hydrogen immediately catches fire.
   • Equation: $$2\text{Na (s)} + 2\text{H}_2\text{O (l)} \rightarrow 2\text{NaOH (aq)} + \text{H}_2\text{ (g)} + \text{Heat energy}$$

2. Calcium (Less Violent - Cold Water):

   • Reacts less violently with cold water. Heat evolved is not sufficient for hydrogen to catch fire. Calcium starts floating because bubbles of hydrogen gas stick to its surface.
   • Equation: $$\text{Ca (s)} + 2\text{H}_2\text{O (l)} \rightarrow \text{Ca(OH)}_2\text{ (aq)} + \text{H}_2\text{ (g)}$$

3. Magnesium (Reacts with Hot Water):

   • Does not react with cold water; reacts with hot water to form magnesium hydroxide and hydrogen gas. It also starts floating.
   • Equation: $$\text{Mg (s)} + 2\text{H}_2\text{O (l) [hot]} \rightarrow \text{Mg(OH)}_2\text{ (aq)} + \text{H}_2\text{ (g)}$$

4. Iron (Reacts only with Steam):

   • Does not react with cold or hot water, but reacts with steam to form iron oxide and hydrogen gas.
   • Equation: $$3\text{Fe (s)} + 4\text{H}_2\text{O (g) [steam]} \rightarrow \text{Fe}_3\text{O}_4\text{ (s)} + 4\text{H}_2\text{ (g)}$$