1. How will you test for a gas which is liberated when HCl reacts with an active metal? (CBSE 2008)
Answer: Hydrogen gas is liberated when an active metal reacts with hydrochloric acid. For testing the presence of hydrogen gas, bring a burning candle near the mouth of the test tube in which the reaction is taking place. If the gas burns with a popping sound, then it can be concluded that it is hydrogen.
2. What is baking powder? How does it make the cake soft and spongy?
Answer: Baking powder is mixed with the flour. When water is added to this flour to make dough, baking powder undergoes a chemical reaction during which carbon dioxide gas is produced. This carbon dioxide gas gets trapped into the dough and bubbles out which causes the cake to rise making it soft and spongy.
3. Give Arrhenius definition of an acid and a base. (CBSE 2009)
Answer: According to Arrhenius theory, acids are substances that produce H+ ions when mixed with water. On the other hand, bases are substances that produce OH- ions when mixed with water.
4. What happens chemically when quick lime is added to water? (CBSE 2008)
Answer: When Calcium oxide i.e. quick lime is added to water, it reacts vigorously with water to produce slaked lime (calcium hydroxide) releasing a large amount of heat.
5. Why does 1 M HCL solutions have a higher concentration of H+ ions than 1M CH3COOH solution? (AI CBSE 2009)
Answer: HCl is a stronger acid than CH^COOH. When added to water, HC1 dissociates almost completely to give H+ ions. In contrast, in the case of CH3COOH, only partial ionisation occurs. This is why 1M HCl solution has a higher concentration of H+ ions than 1M, CH3COOH solution.