HESI A2
HESI A2 Chemistry Practice Test
1. Which law is expressed by the equation: Ptot = Pa + Pb, where P represents pressure, Ptot is the total pressure, and Pa and Pb are component pressures?
- A. Henry's law
- B. Dalton's law
- C. Boyle's law
- D. Gay-Lussac's law
Correct answer: B
Rationale: The correct answer is B, Dalton's law. Dalton's law states that in a mixture of non-reacting gases, the total pressure is equal to the sum of the partial pressures of the individual gases. The equation Ptot = Pa + Pb represents Dalton's law, where Ptot is the total pressure, and Pa and Pb are the component pressures. Choice A, Henry's law, deals with the solubility of gases in liquids. Choice C, Boyle's law, describes the inverse relationship between the pressure and volume of a gas at constant temperature. Choice D, Gay-Lussac's law, states that the pressure of a gas is directly proportional to its absolute temperature when volume is constant.
2. How are elements arranged in the periodic table?
- A. Order of increasing atomic number
- B. Alphabetical order
- C. Order of increasing metallic properties
- D. Order of increasing neutron content
Correct answer: A
Rationale: In the periodic table, the elements are arranged in order of increasing atomic number. This organization is based on the number of protons in the nucleus of each element. It provides a systematic way to classify elements and predict their properties. Knowing the atomic number of an element helps determine its placement in the periodic table and its characteristics. Therefore, the correct answer is the order of increasing atomic number as it is fundamental to the structure and properties of the elements. Choices B, C, and D are incorrect. Alphabetical order does not reflect any underlying property of the elements, metallic properties vary across the table, and neutron content alone is not the basis for the arrangement in the periodic table.
3. Which of the following is defined as the number of cycles of a wave that move past a fixed observation point per second?
- A. Wave
- B. Wavelength
- C. Frequency
- D. Wavefunction
Correct answer: C
Rationale: Frequency is defined as the number of cycles of a wave that pass a fixed observation point per second. It is a fundamental characteristic of a wave and is measured in Hertz (Hz). The frequency of a wave determines its pitch in the case of sound waves and its color in the case of light waves. Choice A, 'Wave,' is incorrect because a wave refers to the disturbance or oscillation that travels through a medium. Choice B, 'Wavelength,' is incorrect as it represents the distance between two corresponding points on a wave (e.g., crest to crest). Choice D, 'Wavefunction,' is not the correct answer as it is a mathematical function used in quantum mechanics to describe the behavior of particles and systems.
4. Which, if any, of these statements about solubility is correct?
- A. The solubility of a substance is defined as its concentration in a saturated solution
- B. Substances with solubilities much less than 1 g/100 mL of solvent are generally considered insoluble
- C. A saturated solution is one that cannot dissolve any more solute
- D. All of these statements are correct
Correct answer: D
Rationale: A. The solubility of a substance is indeed defined as the concentration of a solute that can be dissolved in a solvent to form a saturated solution at a specific temperature and pressure. B. Substances with solubilities much less than 1 g/100 mL of solvent are generally considered insoluble because they do not dissolve in significant amounts in the solvent. C. A saturated solution is one that cannot dissolve any more solute as it has reached its maximum capacity at a specific temperature and pressure. Therefore, all the statements provided are correct, making option D the correct answer.
5. What is a balanced equation?
- A. A description where reactants and products are not equal
- B. An equation where the number of each type of atom is the same on both sides
- C. A chemical formula showing only reactants
- D. An equation without coefficients
Correct answer: B
Rationale: A balanced equation is one where the number of each type of atom is the same on both sides, fulfilling the law of conservation of mass. This principle ensures that the total number of atoms of each element is equal in both reactants and products, signifying that no atoms are created or destroyed, but rather rearranged. Choice A is incorrect because a balanced equation has equal numbers of atoms in the reactants and products. Choice C is incorrect as a balanced equation includes both reactants and products. Choice D is incorrect because coefficients are essential in balancing equations by adjusting the number of atoms present.
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