HESI A2
Chemistry HESI A2 Practice Test
1. What is the correct name of AgNO₃?
- A. Argent nitrous
- B. Argent oxide
- C. Silver nitrite
- D. Silver nitrate
Correct answer: D
Rationale: The correct name for AgNO₃ is silver nitrate. In chemical nomenclature, the element symbol Ag represents silver, and the polyatomic ion NO₃ is known as nitrate. Therefore, when the silver ion (Ag⁺) combines with the nitrate ion (NO₃⁻), the resulting compound is named silver nitrate (AgNO₃). Choices A, B, and C are incorrect because they do not accurately represent the composition of AgNO₃. Argent nitrous (Choice A) and Argent oxide (Choice B) do not reflect the correct anion, and Silver nitrite (Choice C) uses a different anion altogether.
2. What is the correct name of MgO?
- A. Manganese oxide
- B. Magnesium oxide
- C. Magnesium oxate
- D. Magnesium hydroxide
Correct answer: B
Rationale: The correct name of MgO is Magnesium oxide. Mg represents the chemical symbol for magnesium, and O represents the chemical symbol for oxygen. When these elements combine, they form magnesium oxide. Option A, Manganese oxide, is incorrect as it refers to a compound of manganese and oxygen, not magnesium. Option C, Magnesium oxate, is not a valid chemical compound name. Option D, Magnesium hydroxide, refers to a different compound consisting of magnesium, oxygen, and hydrogen.
3. What is the molarity of a solution containing 45 moles of NaCl in 4 liters?
- A. 0.11 M NaCl
- B. 0.45 M NaCl
- C. 1.8 M NaCl
- D. 8.9 M NaCl
Correct answer: A
Rationale: To calculate the molarity of a solution, you use the formula: Molarity (M) = moles of solute / liters of solution. In this case, M = 45 moles / 4 L = 11.25 M. The correct answer is 0.11 M NaCl. Choice B is incorrect as it doesn't match the calculated value. Choice C is also incorrect as it is significantly higher than the correct molarity. Choice D is incorrect as it is excessively high compared to the calculated value.
4. Which element is a metalloid?
- A. Silicon
- B. Lead
- C. Helium
- D. Aluminum
Correct answer: A
Rationale: The correct answer is 'Silicon.' Silicon is a metalloid, which means it has properties of both metals and nonmetals. It is commonly used in electronic devices due to its semiconductor properties. Lead (Choice B) is a metal, Helium (Choice C) is a noble gas, and Aluminum (Choice D) is a metal.
5. What is the name of the device that separates gaseous ions by their mass-to-charge ratio?
- A. mass spectrometer
- B. interferometer
- C. magnetometer
- D. capacitance meter
Correct answer: A
Rationale: A mass spectrometer is a device specifically designed to separate gaseous ions based on their mass-to-charge ratio. This separation process involves ionization, acceleration of the sample, and the deflection of ions in a magnetic field according to their mass-to-charge ratio. The other options, 'interferometer,' 'magnetometer,' and 'capacitance meter,' do not perform the specific function of separating gaseous ions based on their mass-to-charge ratio, making them incorrect choices.
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