HESI A2 Chemistry Practice Questions

HESI A2 Chemistry Practice Questions Related

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Which best defines the molarity of an aqueous sugar solution?

  • A. Grams of sugar per milliliter of solution
  • B. Moles of sugar per milliliter of solution
  • C. Grams of sugar per liter of solution
  • D. Moles of sugar per liter of solution
Correct Answer: D

Rationale: The molarity of a solution is defined as the number of moles of solute per liter of solvent. In the case of an aqueous sugar solution, the molarity would be expressed as moles of sugar per liter of solution. This is because molarity is a measurement of the concentration of a solute in a solution based on the number of moles present in a given volume of the solution. Therefore, the correct answer is D. Choices A, B, and C are incorrect because the molarity is specifically defined in terms of moles of solute per liter of solution, not in grams per milliliter or grams per liter. Molarity is a unit of concentration that relates the amount of solute to the volume of the solution, not the mass of the solute.

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What happens in a single displacement reaction?

  • A. A compound decomposes into two substances.
  • B. An active element displaces a less active element.
  • C. A precipitate solid forms from the reaction of two solutions.
  • D. The oxidation states of atoms in the reactants change.
Correct Answer: B

Rationale: In a single displacement reaction, an active element displaces a less active element in a compound. This process involves one element replacing another in a compound, resulting in the formation of a new compound. Option A is incorrect because a single displacement reaction does not involve the decomposition of a compound into two substances. Option C is incorrect because it describes a precipitation reaction, not a single displacement reaction. Option D is incorrect because it describes oxidation-reduction reactions, not specifically single displacement reactions.

What is the oxidation state of the potassium ion in the compound KCl?

  • A. +1
  • B. -1
  • C. +2
  • D. -2
Correct Answer: A

Rationale: In the compound KCl (potassium chloride), potassium is in Group 1 of the periodic table, which means it has a valence electron of 1. Chlorine is in Group 17 and gains one electron to achieve a stable electron configuration by forming an ionic bond with potassium. As a result, the potassium ion in KCl has a +1 oxidation state. Therefore, the correct answer is +1. Choices B, C, and D are incorrect as they do not reflect the oxidation state of the potassium ion in KCl.

What is the charge of a beta particle?

  • A. -1
  • B. +1
  • C. +2
  • D. No charge
Correct Answer: A

Rationale: A beta particle has a charge of -1. Beta particles are high-energy, high-speed electrons emitted during radioactive decay processes. Since electrons carry a charge of -1, beta particles also carry a charge of -1. This negative charge indicates that beta particles are negatively charged. Option B is incorrect as it suggests a positive charge, which is not the case for beta particles. Option C is incorrect as it indicates a higher positive charge, which is not true for beta particles. Option D is incorrect as beta particles do have a charge, which is negative.

Which one does not name a polar molecule?

  • A. NH₃
  • B. Hâ‚‚S
  • C. SOâ‚‚
  • D. COâ‚‚
Correct Answer: A

Rationale: The correct answer is NH₃. The molecule NH₃ does not represent a polar molecule because nitrogen and hydrogen in this molecule have a small difference in electronegativity that does not result in a significant polar covalent bond. In contrast, molecules H₂S, SO₂, and CO₂ have polar covalent bonds due to larger electronegativity differences, making them polar molecules. Therefore, options B, C, and D are polar molecules, unlike option A.

How many neutrons are in an atom of helium-4?

  • A. 2
  • B. 3
  • C. 4
  • D. 6
Correct Answer: A

Rationale: The atomic number of helium is 2, indicating it has 2 protons. Helium-4, the most common isotope of helium, has 2 neutrons in addition to its 2 protons. Therefore, the correct answer is 2 neutrons in an atom of helium-4. Choice B, C, and D are incorrect as they do not match the correct composition of helium-4, which consists of 2 protons and 2 neutrons.

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