HESI A2
HESI A2 Chemistry Questions
Question 1 of 5
What color does phenolphthalein turn in the presence of an acid?
Correct Answer: C
Rationale: The correct answer is C, pink. Phenolphthalein is colorless in acidic solutions and turns pink in the presence of a base due to a shift in pH causing a structural change. This color change is a result of the molecule's ability to act as a pH indicator, making it ideal for titrations. Choice A, clear, is incorrect as phenolphthalein is not colorless in the presence of an acid. Choice B, blue, is incorrect as phenolphthalein does not turn blue in any pH range. Choice D, red, is incorrect as phenolphthalein turns pink, not red, in the presence of a base.
Question 2 of 5
You contain two odorous gases in vials with porous plugs. Gas A has twice the mass of Gas B. Which observation is most likely?
Correct Answer: A
Rationale: The correct answer is A because the rate of effusion of a gas is inversely proportional to the square root of its molar mass, assuming the same conditions. Since Gas A has twice the mass of Gas B, Gas B will effuse faster. Therefore, you will smell Gas A before you smell Gas B. Choice B is incorrect because Gas B will be smelled first due to its faster effusion rate. Choices C and D are incorrect because both gases will eventually be smelled due to their odorous nature, but the order of detection is based on effusion rates, not presence or absence of smell.
Question 3 of 5
The three important allotropic forms of phosphorus are red, white, and ___________.
Correct Answer: C
Rationale: The correct answer is C: black. Red and white phosphorus are well-known allotropes. Black phosphorus is another important allotrope with a layered structure. It is stable at room temperature and has unique electronic properties. Green, gray, and silver are not commonly recognized allotropic forms of phosphorus, making them incorrect choices.
Question 4 of 5
How much concentrated HCl should be used to prepare 500 mL of a 0.100 M HCl solution?
Correct Answer: B
Rationale: To prepare a 0.100 M solution, we use the formula M1V1 = M2V2. Given M1=concentration of concentrated HCl, V1=volume of concentrated HCl, M2=desired concentration, V2=final volume. Plugging in the values, we get M1(unknown volume) = 0.100 M x 500 mL. Solving for the unknown volume, we find V1 = (0.100 M x 500 mL) / M1. As we want to find the volume of concentrated HCl needed, we isolate V1. Therefore, V1 = 100 mL. This corresponds to choice B as the correct answer. Choices A, C, and D are incorrect as they do not match the calculated volume needed to prepare the 0.100 M HCl solution.
Question 5 of 5
Here are the solubilities of four substances at 0�C, in grams of solute per 100 mL of water. If the temperature increases to 20�C, what would you expect to happen to the solubility figures?
Correct Answer: C
Rationale: Failed to generate a rationale after 5 retries.
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