HESI A2
HESI A2 Chemistry Practice Test
1. 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.
2. Which type of radiation emits helium ions and can be stopped by a piece of paper?
- A. Beta radiation
- B. Alpha radiation
- C. Gamma radiation
- D. X-ray radiation
Correct answer: B
Rationale: Alpha radiation emits helium ions, which are helium nuclei without electrons, making them positively charged. These ions are relatively large and heavy compared to beta and gamma radiation. Due to their size and charge, alpha particles interact strongly with matter and are easily stopped. A piece of paper or even human skin can effectively block alpha radiation. Therefore, alpha radiation is the type of radiation that can be stopped by a piece of paper. Beta radiation consists of fast-moving electrons and can penetrate further into materials than alpha radiation, thus not stopped by a piece of paper. Gamma radiation is highly penetrating and requires dense materials like lead or concrete to block it effectively. X-ray radiation, similar to gamma radiation, is also highly penetrating and cannot be stopped by a piece of paper.
3. Bonds involve electrons that are not equally shared, and may be deemed as an intermediate between the extremes represented by and bonds.
- A. Ionic bonds
- B. Covalent bonds
- C. Chemical bonds
- D. Polar bonds
Correct answer: C
Rationale: Chemical bonds involve electrons that are not equally shared, and may be deemed as an intermediate between the extremes represented by covalent and ionic bonds. This is the most accurate statement among the choices as it correctly describes the nature of chemical bonds, highlighting their intermediate position between covalent bonds (where electrons are shared) and ionic bonds (where electrons are transferred). 'Ionic bonds' (choice A) are not the correct answer because they represent a type of chemical bond where electrons are transferred, not shared. 'Covalent bonds' (choice B) are not the correct answer either because they represent a type of chemical bond where electrons are shared equally. 'Polar bonds' (choice D) are not the correct answer as they involve an unequal sharing of electrons but do not represent the intermediate position between covalent and ionic bonds as chemical bonds do. Therefore, the correct answer is 'Chemical bonds.'
4. A molecule of water contains hydrogen and oxygen in a 1:8 ratio by mass. This is a statement of _____.
- A. The law of multiple proportions
- B. The law of conservation of mass
- C. The law of conservation of energy
- D. The law of constant composition
Correct answer: D
Rationale: The statement that a molecule of water contains hydrogen and oxygen in a 1:8 ratio by mass is an example of the law of constant composition. This law states that all samples of a given chemical compound have the same elemental composition. In the case of water (H2O), no matter where you obtain a sample of water, it will always be composed of hydrogen and oxygen in a 1:8 ratio by mass. The law of multiple proportions deals with compounds that can be formed by the combination of elements in different ratios. The law of conservation of mass states that mass is neither created nor destroyed in a chemical reaction. The law of conservation of energy states that energy cannot be created or destroyed, only transferred or converted.
5. What is the spontaneous, random movement of small particles suspended in a liquid, caused by the unbalanced impacts of molecules on the particle?
- A. Brownian motion
- B. Grey's kinesis
- C. Boyle's wave
- D. None of the above
Correct answer: A
Rationale: Brownian motion is the correct choice as it specifically refers to the spontaneous, random movement of small particles suspended in a liquid, caused by the unbalanced impacts of molecules on the particle. This phenomenon was observed and documented by Robert Brown, leading to the discovery of the existence of molecules. Grey's kinesis and Boyle's wave are not scientifically recognized terms related to this concept.
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