E. Answer the following.
1.Give an example of change in colour in a chemical reaction.
2. Give an example of formation of precipitate in a chemical reaction.
3. Give an example of evolution of a gas in a chemical reaction.
4. Give an example of evolution of heat in a chemical reaction.
5. Name a chemical that is used to identify ammonia gas.
Answers
Answer:
1. Copper reacts with oxygen, H2O and CO2 to give copper carbonate, which changes color from brown to blue or blue green.
2. sometimes the pipes in our homes get clogged because precipitates of magnesium and calcium oxides have deposited themselves within the pipes. This can happen with "hard" water.
3. when zinc reacts with hydrochloric acid, hydrogen gas is evolved with formation of zinc chloride.
4. 2 H2O(g) → 2 H2(g) + O2(g) Generally, evolution of heat in a reaction favours the conversion of reactants to products.
5. Ammonium ions can be identified in a solution by adding dilute sodium hydroxide solution and gently heating. If ammonium ions are present, they will be converted to ammonia gas. Ammonia has a characteristic choking smell. It also turns damp red litmus paper or damp universal indicator paper blue.