which ion would you expect to dominate in water solutions of bases

HESI A2

Chemistry HESI A2 Practice Test

1. Which ion would you expect to dominate in water solutions of bases?

A. MgCl₂
B. 2HCl
C. H⁺
D. OH⁻

Correct answer: D

Rationale: In water solutions of bases, the dominant ion would be OH⁻ (hydroxide ion). Bases release OH⁻ ions when dissolved in water, increasing the concentration of hydroxide ions and leading to a higher pH. This is in contrast to acids, which release H⁺ ions. Therefore, in water solutions of bases, the presence of OH⁻ ions signifies the basic nature of the solution. Choices A, B, and C are incorrect because MgCl₂ is a salt, 2HCl is a compound consisting of two hydrogen ions and one chloride ion, and H⁺ represents a hydrogen ion typically associated with acids, not bases.

2. Which element has the highest atomic number?

A. Uranium
B. Hydrogen
C. Radon
D. Bismuth

Correct answer: A

Rationale: The correct answer is Uranium. The atomic number represents the number of protons in an atom's nucleus. Among the options provided, Uranium has the highest atomic number, which is 92. Hydrogen has an atomic number of 1, Radon has an atomic number of 86, and Bismuth has an atomic number of 83. Therefore, Uranium is the element with the highest atomic number in the given choices.

3. What is the oxidation state of the oxygen atom in the compound NaOH?

A. -2
B. -1
C. 0
D. +2

Correct answer: B

Rationale: In the compound NaOH (sodium hydroxide), the oxidation state of the sodium ion (Na) is +1 as it commonly has a +1 charge in ionic compounds. Oxygen (O) typically has an oxidation state of -2 in most compounds. Since the compound is electrically neutral and the overall charge is zero, the sum of the oxidation states of all atoms in the compound must be zero. Therefore, considering that sodium has an oxidation state of +1, the oxygen atom in NaOH must have an oxidation state of -1 to balance the charges and overall neutrality of the compound. Choice A (-2) is incorrect as this is not the oxidation state of oxygen in this compound. Choice C (0) is incorrect as oxygen in NaOH does not have an oxidation state of 0. Choice D (+2) is incorrect as oxygen typically has a negative oxidation state in compounds, not a positive one.

4. What charge do Group VIIA elements have?

A. -1
B. -2
C. 0
D. 1

Correct answer: A

Rationale: Group VIIA elements, also known as halogens, have a tendency to gain one electron to achieve a stable electron configuration, resulting in a -1 charge. This is because they have seven valence electrons and need one more to complete their octet, making them highly reactive in forming -1 ions. Therefore, the correct answer is A. Choice B (-2) is incorrect because Group VIIA elements typically gain one electron, not two. Choice C (0) is incorrect as these elements tend to form -1 ions by gaining one electron. Choice D (1) is incorrect because Group VIIA elements gain electrons to form negative ions, not positive ones.

5. Which of the following is a colligative property of a solution?

A. Freezing point depression
B. Viscosity
C. Surface tension
D. Boiling point elevation

Correct answer: A

Rationale: A colligative property is a property that depends on the number of solute particles in a solution, not on the identity of the solute particles. Freezing point depression is one such property, where adding a solute to a solvent lowers the freezing point of the solution compared to the pure solvent. This phenomenon occurs because the presence of solute particles disrupts the formation of the regular crystal lattice structure, requiring a lower temperature for solidification to occur. Choices B, C, and D are not colligative properties. Viscosity and surface tension are not dependent on the number of solute particles but on intermolecular forces and molecular interactions. Boiling point elevation is another colligative property, but in this case, the question asked for a colligative property of a solution, making freezing point depression the correct answer.