if gas a has four times the molar mass of gas b you would expect it to diffuse through a plug

HESI A2

Chemistry HESI A2 Practice Test

1. If gas A has four times the molar mass of gas B, you would expect it to diffuse through a plug ___________.

A. at half the rate of gas B
B. at twice the rate of gas B
C. at a quarter the rate of gas B
D. at four times the rate of gas B

Correct answer: A

Rationale: When comparing the diffusion rates of two gases, according to Graham's law of diffusion, the rate of diffusion is inversely proportional to the square root of the molar mass. If gas A has four times the molar mass of gas B, the square root of the molar masses ratio (4:1) is 2. This means that gas A would diffuse through a plug at half the rate of gas B. Therefore, the correct answer is A, at half the rate of gas B. Choices B, C, and D are incorrect because they do not reflect the correct relationship between the molar masses and the rates of diffusion according to Graham's law.

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

A. Clear
B. Blue
C. Pink
D. Red

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.

3. Which substance causes a drop to rapidly turn litmus dye from blue to red?

A. Milk
B. Sea water
C. Ammonia
D. Lemon juice

Correct answer: D

Rationale: Lemon juice is the correct answer as it is acidic in nature. Acids like lemon juice release hydrogen ions when dissolved in water, which causes litmus dye to change color from blue to red. Milk (Choice A) is neutral, sea water (Choice B) is slightly alkaline, and ammonia (Choice C) is a base. Therefore, these substances do not cause litmus dye to change from blue to red.

4. What type of starch is glycogen?

A. Plant starch
B. Animal starch
C. Glucose
D. Cellulose

Correct answer: B

Rationale: Glycogen is classified as animal starch, not plant starch. It is the storage form of glucose in animals, primarily found in the liver and muscles. Choice A (Plant starch) is incorrect because glycogen is not derived from plants. Choice C (Glucose) is incorrect as glucose is a monosaccharide and not a type of starch. Choice D (Cellulose) is incorrect as cellulose is a structural polysaccharide found in plant cell walls, not the same as glycogen.

5. Which substance shows a decrease in solubility in water with an increase in temperature?

A. NaCl
B. O
C. KI
D. CaCl

Correct answer: C

Rationale: Potassium iodide (KI) shows a decrease in solubility in water with an increase in temperature. This is due to the dissolution of KI in water being an endothermic process. When the temperature rises, the equilibrium shifts toward the solid state, leading to a decrease in solubility. Therefore, as the temperature increases, KI becomes less soluble in water. Choice A (NaCl) and Choice D (CaCl) do not exhibit a decrease in solubility with an increase in temperature. NaCl and CaCl are generally more soluble in water at higher temperatures. Choice B (Oxygen) is a gas and not typically considered in solubility discussions involving solids or liquids dissolving in water.