HESI A2
Chemistry HESI A2 Practice Test
1. To the nearest whole number, what is the mass of one mole of water?
- A. 16 g/mol
- B. 18 g/mol
- C. 20 g/mol
- D. 22 g/mol
Correct answer: B
Rationale: The molar mass of water (H₂O) is calculated by adding the atomic masses of two hydrogen atoms (each with a molar mass of approximately 1 g/mol) and one oxygen atom (with a molar mass of approximately 16 g/mol). Therefore, the molar mass of water is approximately 18 g/mol, making choice B the correct answer. Choice A (16 g/mol) is incorrect because it represents the molar mass of oxygen, not water. Choices C (20 g/mol) and D (22 g/mol) are incorrect as they do not correspond to the molar mass of water.
2. What is an alloy in which another metal is dissolved in mercury (Hg) called?
- A. Electrum
- B. Amalgam
- C. Solder
- D. Bronze
Correct answer: B
Rationale: An amalgam is a type of alloy where another metal is dissolved in mercury (Hg). This process forms a unique mixture that has various applications in dentistry, chemistry, and other fields. Electrum is a natural alloy of gold and silver, solder is a metal alloy used to join other metals together, and bronze is a copper-tin alloy. Therefore, the correct answer is B - Amalgam.
3. What is the number of protons in the atomic nucleus of an alkali metal?
- A. 9
- B. 10
- C. 11
- D. 12
Correct answer: C
Rationale: The number of protons in the atomic nucleus of an alkali metal is 11. Alkali metals, belonging to group 1 of the periodic table, have 1 electron in their outer shell, which corresponds to 1 proton in their nucleus. Therefore, the correct answer is option C: 11. Choice A (9) is incorrect because it does not match the number of protons in an alkali metal. Choice B (10) is incorrect as it is also not the correct number of protons for an alkali metal. Choice D (12) is incorrect as it is not the typical number of protons found in the nucleus of an alkali metal.
4. Radioactive isotopes are frequently used in medicine. What kind of half-life would a medical isotope probably have?
- A. Seconds-long
- B. Days-long
- C. Years-long
- D. Many years long
Correct answer: B
Rationale: Medical isotopes used in diagnosis and treatment need to have a relatively short half-life to minimize radiation exposure to patients. If the half-life were too long (such as many years) or even years-long, the radiation would persist for too long and could be harmful to the patient. Seconds-long half-lives would not provide enough time for the isotope to be effective. Days-long half-lives strike a balance between providing enough time for the isotope to be used effectively and minimizing radiation exposure.
5. What is the correct formula for silver hydroxide?
- A. AgO
- B. AgOH
- C. AgH
- D. AgH₂O
Correct answer: B
Rationale: The correct formula for silver hydroxide is AgOH. Silver hydroxide is formed by the combination of the silver ion (Ag⁺) with the hydroxide ion (OH⁻) to create AgOH. It is essential to note that the hydroxide ion consists of one oxygen and one hydrogen atom, thus the formula AgOH. Choices A, C, and D are incorrect as they do not accurately represent the composition of silver hydroxide.
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