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Question 1:

What is the role of an acid-base indicator?

A) To measure the pH of a solution
B) To indicate the presence of acids in a solution
C) To determine the molarity of a solution
D) To detect the presence of bases in a solution

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Explanation: The correct answer is A) To measure the pH of a solution. Acid-base indicators are substances that change color in response to changes in pH. They are used to measure the pH of a solution by indicating whether it is acidic, neutral, or basic based on the observed color change. Different indicators have different color transitions at specific pH ranges.

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Question 2:

Which of the following is a commonly used acid-base indicator?

A) Methylene blue
B) Sodium chloride
C) Potassium permanganate
D) Phenolphthalein

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Explanation: The correct answer is D) Phenolphthalein. Phenolphthalein is a commonly used acid-base indicator. It is colorless in acidic solutions and turns pink or magenta in basic solutions. This color change makes it useful for indicating the endpoint in acid-base titrations.

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Question 3:

At what pH range does bromothymol blue change color?

A) Below pH 4.6
B) Between pH 4.6 and 6.0
C) Between pH 6.0 and 7.6
D) Above pH 7.6

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Explanation: The correct answer is C) Between pH 6.0 and 7.6. Bromothymol blue is an acid-base indicator that changes color in the pH range of 6.0 to 7.6. It appears yellow in acidic solutions and blue in basic solutions within this pH range.

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Question 4:

Which acid-base indicator is commonly used in pH testing strips?

A) Litmus
B) Bromocresol green
C) Thymol blue
D) Alizarin yellow

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Explanation: The correct answer is A) Litmus. Litmus is a commonly used acid-base indicator in pH testing strips. It is available as blue litmus paper and red litmus paper. Blue litmus paper turns red in acidic solutions and remains blue in basic or neutral solutions, while red litmus paper turns blue in basic or neutral solutions and remains red in acidic solutions.

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Question 5:

Which acid-base indicator is commonly used to detect the endpoint in acid-base titrations?

A) Methyl red
B) Bromothymol blue
C) Congo red
D) Cresol red

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Explanation: The correct answer is A) Methyl red. Methyl red is a commonly used acid-base indicator to detect the endpoint in acid-base titrations. It changes color from red to yellow at a pH range of 4.4 to 6.2, indicating the completion of the reaction between the acid and base. The color change of methyl red at this pH range provides a visual indicator of the endpoint.