Q21. What pH range characterizes acidic substances on the pH scale?
a) 0-4
b) 5-7
c) 7-10
d) 11-14
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Correct Answer: a) 0-4
Explanation: Acidic substances have pH values ranging from 0 to 4 on the pH scale. The lower the pH value, the stronger the acid. Common examples of acidic substances include lemon juice, vinegar, and battery acid.
Q22. Which of the following substances is commonly used to increase the pH of acidic water in fish tanks?
a) Salt
b) Vinegar
c) Baking soda
d) Lemon juice
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Correct Answer: c) Baking soda
Explanation: Baking soda (sodium bicarbonate) is commonly used to increase the pH of acidic water in fish tanks. It acts as a buffer, helping to stabilize the pH and create a suitable environment for fish and other aquatic organisms.
Q23. What is the pH of a solution that is considered weakly basic?
a) pH 5
b) pH 7
c) pH 8
d) pH 10
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Correct Answer: c) pH 8
Explanation: A solution with a pH of 8 is considered weakly basic. pH values between 7.1 and 14 are classified as basic, with higher values indicating stronger alkalinity. Examples of weakly basic substances include baking soda solution and seawater.
Q24. Which of the following substances is commonly used to lower the pH of alkaline soil for plants that prefer acidic conditions?
a) Lime
b) Vinegar
c) Ammonia
d) Sulfur
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Correct Answer: a) Lime
Explanation: Lime is commonly used to lower the pH of alkaline soil for plants that prefer acidic conditions. It acts as a soil amendment by neutralizing soil acidity and raising the pH to create a more suitable environment for acid-loving plants.
Q25. What pH range characterizes basic or alkaline substances on the pH scale?
a) 0-4
b) 5-7
c) 7-10
d) 11-14
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Correct Answer: d) 11-14
Explanation: Basic or alkaline substances have pH values ranging from 11 to 14 on the pH scale. The higher the pH value, the stronger the base. Examples of basic substances include bleach, ammonia, and oven cleaner.
Q26. Which of the following substances is commonly used to lower the pH of swimming pool water?
a) Lemon juice
b) Vinegar
c) Baking soda
d) Hydrochloric acid
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Correct Answer: d) Hydrochloric acid
Explanation: Hydrochloric acid is commonly used to lower the pH of swimming pool water. It is added to pool water to reduce alkalinity and maintain the pH within the ideal range for swimming. Care must be taken when handling hydrochloric acid due to its corrosive nature.
Q27. What is the pH of a solution that is neither acidic nor basic?
a) pH 1
b) pH 7
c) pH 9
d) pH 14
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Correct Answer: b) pH 7
Explanation: A solution with a pH of 7 is considered neutral. This means it has an equal concentration of hydrogen ions (H⁺) and hydroxide ions (OH⁻), resulting in a balanced pH. Pure water at room temperature is an example of a neutral solution.
Q28. Which of the following substances is commonly used to increase the pH of acidic soil for agriculture?
a) Sulfuric acid
b) Lime
c) Vinegar
d) Lemon juice
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Correct Answer: b) Lime
Explanation: Lime is commonly used to increase the pH of acidic soil for agriculture. It acts as a soil amendment by neutralizing soil acidity and raising the pH to create a more suitable environment for crops and plants.
Q29. What is the pH of a solution that is considered weakly acidic?
a) pH 2
b) pH 7
c) pH 8
d) pH 10
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Correct Answer: a) pH 2
Explanation: A solution with a pH of 2 is considered weakly acidic. pH values between 0 and 6.9 are classified as acidic, with lower values indicating stronger acidity. Examples of weakly acidic substances include coffee and vinegar.
Q30. Which of the following substances is commonly used to test the pH of solutions?
a) Salt
b) Vinegar
c) Litmus paper
d) Aluminium foil
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Correct Answer: c) Litmus paper
Explanation: Litmus paper is commonly used to test the pH of solutions. It contains a mixture of dyes that change colour depending on the acidity or alkalinity of the solution being tested. Blue litmus paper turns red in acidic solutions and red litmus paper turns blue in basic solutions.