Question 1: What happens when a solution of an acid is mixed with a solution of a base in a test tube?
Explanation: When aqueous solution an acid is mixed with aqueous solution of a base, then neutralization reaction takes place. Neutralization reaction is exothermic in nature and results in formation of salt.
Question 2: An aqueous solution turns red litmus solution blue. Excess addition of which of the following solution would reverse the change?
Explanation: Since the given solution is turning red litmus solution to blue, it is a basic solution. So, addition of an acid would reverse the change.
Question 3: During the preparation of hydrogen chloride gas on a humid day, the gas is usually passed through the guard tube containing calcium chloride. The role of calcium chloride taken in the guard tube is to
Explanation: The humid day in first sentence gives the clue. Had it been some other option then guard tube should have been used in all cases, whether the day was humid or dry.
Question 4: Which of the following salts does not contain water of crystallisation?
Explanation: Baking soda is anhydrous form of sodium bicarbonate. Blue vitriol gets its characteristic blue color due to water of crystallization. Presence of two molecules of water of crystallization in one molecule of Gypsum makes it a hard substance, while removal of 1.5 molecules of water of crystallization makes it Plaster of Paris. Washing soda is prepared by hydrating soda ash.
Question 5: Sodium carbonate is a basic salt because it is a salt of
Explanation: Options a and b would give neutral salts, while option c would give acidic salt.
Question 6: Calcium phosphate is present in tooth enamel. Its nature is
Explanation: Calcium phosphate is formed after neutralization reaction between calcium hydroxide (strong base) and phosphoric acid (weak acid). So, it is a basic salt.
Question 7: A sample of soil is mixed with water and allowed to settle. The clear supernatant solution turns the pH paper yellowish-orange. Which of the following would change the colour of this pH paper to greenish-blue?
Explanation: Yellowish-orange colour of pH paper indicates that soil sample is acidic. So, we need to add a base (antacid) to change the colour of pH paper to greenish blue. Another hint to solve this question can be, options a and b show acids, so they are incorrect options. Common salt cannot be an answer because common salt is neutral.
Question 8: Which of the following gives the correct increasing order of acidic strength?
Explanation: Water is neutral and acidic acid (organic acid) is a weak acid. Hydrochloric acid is a strong acid because it is inorganic acid, unlike acetic acid.
Question 9: If a few drops of a concentrated acid accidentally spills over the hand of a student, what should be done?
Explanation: Washing with plenty of water will help in cooling down the burning sensation which happened due to acid. Paste of sodium hydrogen carbonate will help neutralize the effect of acid. A paste is always better than solution, in terms of sticking for considerable time. Hence, option c is incorrect.
Question 10: Sodium hydrogencarbonate when added to acetic acid evolves a gas. Which of the following statements are true about the gas evolved?
Explanation: When sodium hydrogen carbonate reacts with an acid, it gives carbon dioxide gas. Carbon dioxide turns lime water milky. Carbon dioxide does not support combustion, so it extinguishes burning splinter.
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