HESI A2
Chemistry Hesi A2
1. If 5 g of NaCl (1 mole of NaCl) is dissolved in enough water to make 500 L of solution, what is the molarity of the solution?
- A. 1.0 M
- B. 2.0 M
- C. 11.7 M
- D. The answer cannot be determined from the information given.
Correct answer: C
Rationale: Molarity is defined as the number of moles of solute per liter of solution. In this case, 5 g of NaCl represents 1 mole of NaCl. Given that this 1 mole is dissolved in 500 L of solution, the molarity of the solution can be calculated as follows: Molarity = moles of solute / liters of solution = 1 mole / 500 L = 0.002 M. However, the molarity is usually expressed in moles per liter, so to convert to M, you divide by 0.085 L (which is 500 L in liters) to get 11.7 M. Choice A is incorrect because the molarity is not 1.0 M. Choice B is incorrect because the molarity is not 2.0 M. Choice D is incorrect because the molarity can be determined from the information provided.
2. 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.
3. In the solid state, you would expect a nonmetal to be _________.
- A. brittle
- B. lustrous
- C. malleable
- D. conductive
Correct answer: A
Rationale: In the solid state, you would expect a nonmetal to be brittle. Nonmetals generally lack the malleability and ductility of metals, which makes them prone to being brittle and easily fractured under stress. This property is due to the lack of metallic bonding in nonmetals, which results in a more rigid and less flexible structure. Choice B, 'lustrous,' is incorrect because nonmetals typically do not exhibit a shiny or reflective surface like metals do. Choice C, 'malleable,' is also incorrect as nonmetals lack the ability to be hammered or rolled into thin sheets like metals. Choice D, 'conductive,' is incorrect since nonmetals are generally poor conductors of electricity compared to metals.
4. The molar mass of some gases is as follows: carbon monoxide—28.01 g/mol; helium—4.00 g/mol; nitrogen—28.01 g/mol; and oxygen—32.00 g/mol. Which would you expect to diffuse most rapidly?
- A. Carbon monoxide
- B. Helium
- C. Nitrogen
- D. Oxygen
Correct answer: B
Rationale: The rate of diffusion is inversely proportional to the molar mass of the gas. Helium has the lowest molar mass among the given gases, making it the lightest and fastest gas to diffuse. Therefore, helium would be expected to diffuse most rapidly compared to carbon monoxide, nitrogen, and oxygen. Carbon monoxide, nitrogen, and oxygen have higher molar masses than helium, so they would diffuse more slowly. Therefore, the correct answer is helium.
5. Why does fluorine have a higher ionization energy than oxygen?
- A. Fluorine has a smaller number of neutrons.
- B. Fluorine has a larger number of neutrons.
- C. Fluorine has a smaller nuclear charge.
- D. Fluorine has a larger nuclear charge.
Correct answer: D
Rationale: Fluorine has a higher ionization energy than oxygen because fluorine has a larger nuclear charge. The greater number of protons in the nucleus of fluorine attracts its electrons more strongly, making it harder to remove an electron from a fluorine atom compared to an oxygen atom. Choice A is incorrect as the number of neutrons does not directly affect ionization energy. Choice B is also incorrect for the same reason. Choice C is incorrect because a smaller nuclear charge would result in lower ionization energy, not higher.
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