in the presence of an acid what color is phenolphthalein
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HESI A2

HESI A2 Chemistry

1. What color does phenolphthalein turn in the presence of an acid?

Correct answer: C

Rationale: In the presence of an acid, phenolphthalein turns pink. Phenolphthalein is a pH indicator that is colorless in acidic solutions but turns pink in basic solutions. Therefore, when added to an acidic solution, phenolphthalein will exhibit a pink coloration. Choice A, 'Clear,' is incorrect because phenolphthalein does not remain colorless in the presence of an acid. Choice B, 'Blue,' is incorrect as phenolphthalein does not turn blue in the presence of an acid. Choice D, 'Red,' is incorrect as phenolphthalein does not exhibit a red color in acidic solutions.

2. Which one of the following best describes the function of a cell membrane?

Correct answer: A

Rationale: The correct answer is A. The function of a cell membrane is to control the substances entering and leaving the cell. The cell membrane is selectively permeable, allowing it to regulate the movement of ions and molecules in and out of the cell to maintain internal balance and proper function. Choice B is incorrect because while the cell membrane does provide some structural support, its primary function is not to maintain the cell's shape. Choice C is incorrect because the cell membrane controls both the substances entering and leaving the cell, not just those entering. Choice D is incorrect as the primary function of the cell membrane is not to support the cell's structures but to regulate the movement of substances.

3. What number is 15, if it is 20% of that number?

Correct answer: B

Rationale: To find the number that 15 is 20% of, we set up the equation: x * 0.20 = 15. Solving for x, we get x = 15 / 0.20 = 75. Therefore, 15 is 20% of 75. Choice A, 3, is too small to be 20% of 15. Choice C, 75, is the result of the correct calculation. Choice D, 300, is too large to be 20% of 15.

4. What is the meaning of exocytosis?

Correct answer: B

Rationale: Exocytosis is the process by which a cell releases substances to the outside by fusing with the plasma membrane. During exocytosis, vesicles containing molecules fuse with the cell membrane, allowing the release of the contents outside the cell. This process is crucial for the secretion of various substances such as hormones, enzymes, and neurotransmitters. Choices A, C, and D are incorrect as they describe processes different from exocytosis. Choice A describes endocytosis, where the cell engulfs substances to bring them into the cell. Choice C is more aligned with pinocytosis, the process of engulfing liquid material. Choice D refers to phagocytosis, which is the uptake of solid particles by the cell.

5. At what temperature does water boil in °F?

Correct answer: B

Rationale: Water boils at 212°F under standard atmospheric pressure. This is the point at which water changes from a liquid to a gas phase. Choice A (210°F) is incorrect as it is below the boiling point of water. Choice C (215°F) and Choice D (220°F) are also incorrect as they are above the boiling point of water.

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