aan is a description of a that gives the chemical formulas of the reactants and the of the reaction with coefficients introduced so that the n

HESI A2

HESI A2 Chemistry Practice Test

1. What is a balanced equation?

A. A description where reactants and products are not equal
B. An equation where the number of each type of atom is the same on both sides
C. A chemical formula showing only reactants
D. An equation without coefficients

Correct answer: B

Rationale: A balanced equation is one where the number of each type of atom is the same on both sides, fulfilling the law of conservation of mass. This principle ensures that the total number of atoms of each element is equal in both reactants and products, signifying that no atoms are created or destroyed, but rather rearranged. Choice A is incorrect because a balanced equation has equal numbers of atoms in the reactants and products. Choice C is incorrect as a balanced equation includes both reactants and products. Choice D is incorrect because coefficients are essential in balancing equations by adjusting the number of atoms present.

2. What is the oxidation state of the sulfur atom in sulfuric acid H2SO4?

A. 4
B. 6
C. 8
D. 10

Correct answer: B

Rationale: In sulfuric acid (H2SO4), sulfur has an oxidation state of +6. The oxidation state is determined by considering the overall charge of the compound and the known oxidation states of other elements. In this case, hydrogen is typically +1, and oxygen is -2. To balance the charges and match the compound's overall charge of 0, sulfur must have an oxidation state of +6. Choice A (4) is incorrect because it doesn't balance the charges in the compound. Choices C (8) and D (10) are also incorrect as they are not valid oxidation states for sulfur in this compound.

3. 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.

4. What is a pentose sugar?

A. A 6 carbon sugar
B. A 4 carbon sugar
C. A 5 carbon sugar
D. A 7 carbon sugar

Correct answer: C

Rationale: A pentose is a 5-carbon sugar, as the prefix 'pent-' signifies five. Therefore, a pentose sugar consists of five carbon atoms. Choice A, 'A 6 carbon sugar,' is incorrect as a pentose sugar specifically has five carbons. Choice B, 'A 4 carbon sugar,' is incorrect as it describes a tetrose sugar, which has four carbons. Choice D, 'A 7 carbon sugar,' is incorrect as it does not correspond to the definition of a pentose sugar.

5. Which of the following pH values is most likely for lemon juice?

A. 3
B. 5
C. 7
D. 9

Correct answer: A

Rationale: Lemon juice is highly acidic with a pH around 2-3, making it more acidic than neutral substances. A pH of 5 is too high for lemon juice, indicating less acidity. Similarly, pH 7 is neutral, and pH 9 would be alkaline, which is not characteristic of lemon juice. Therefore, the correct answer is option A (pH 3).