HESI A2
HESI A2 Chemistry Practice Questions
1. Which one is not a hydrocarbon?
- A. Methane (CH4)
- B. Pyridine (C5H5N)
- C. Ethane (C2H6)
- D. Propane (C3H8)
Correct answer: B
Rationale: The correct answer is B, Pyridine (C5H5N). Pyridine is not a hydrocarbon because it contains nitrogen (N) in its molecular structure, in addition to carbon (C) and hydrogen (H) atoms. Hydrocarbons consist solely of carbon and hydrogen atoms. Methane (CH4), ethane (C2H6), and propane (C3H8) are all examples of hydrocarbons as they only contain carbon and hydrogen atoms, making them organic compounds known for their combustion properties.
2. Which of these represents a strong acid?
- A. CH₃COOH
- B. H₂SO₄
- C. NH₃
- D. KOH
Correct answer: B
Rationale: Among the options provided, H₂SO₄ (sulfuric acid) represents a strong acid. Strong acids completely ionize in water to produce a high concentration of H+ ions. Sulfuric acid is a strong acid known for its ability to dissociate almost completely in water, making it a strong acid. Choice A, CH₃COOH (acetic acid), is a weak acid that only partially dissociates in water. Choices C and D, NH₃ (ammonia) and KOH (potassium hydroxide), are bases and not acids.
3. Which of these types of intermolecular force is weakest?
- A. Dipole-dipole interaction
- B. London dispersion force
- C. Hydrogen bonding
- D. Ionic bonding
Correct answer: B
Rationale: The correct answer is B, London dispersion force. London dispersion forces are the weakest type of intermolecular force among the options provided. These forces arise from temporary fluctuations in electron distribution within molecules, leading to temporary dipoles. London dispersion forces are present in all molecules and are generally weaker than dipole-dipole interactions, hydrogen bonding, and ionic bonding. Dipole-dipole interactions are stronger than London dispersion forces as they involve permanent dipoles in molecules. Hydrogen bonding is stronger than both London dispersion and dipole-dipole interactions as it is a special type of dipole-dipole interaction that occurs when hydrogen is bonded to highly electronegative atoms like oxygen or nitrogen. Ionic bonding is the strongest type of intermolecular force among the options, but it is not the correct answer for the weakest type of force.
4. 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.
5. What is the net charge of an ionic compound?
- A. 0
- B. -1
- C. +1
- D. Variable
Correct answer: A
Rationale: The correct answer is A: 0. Ionic compounds have a net charge of 0 because they are formed by the combination of positively charged ions (cations) and negatively charged ions (anions) in a way that neutralizes their charges. This balanced combination results in an electrically neutral compound. Therefore, the net charge of an ionic compound is typically 0. Choices B, C, and D are incorrect because ionic compounds are designed to have a total neutral charge, with the positive charges balancing out the negative charges.
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