HESI A2
Chemistry HESI A2 Quizlet
1. What is the chemical reaction that involves breaking down a compound into component parts?
- A. Decomposition
- B. Synthesis
- C. Combustion
- D. Single replacement
Correct answer: A
Rationale: Decomposition is the correct answer because in a decomposition reaction, a compound is broken down into simpler substances. This type of reaction involves the splitting of a compound into its component parts, often through the use of heat, light, or electricity. Synthesis (choice B) is the opposite process where simpler substances are combined to form a more complex compound. Combustion (choice C) is a reaction involving rapid oxidation often accompanied by heat and light. Single replacement (choice D) is a reaction where one element replaces another in a compound.
2. What is the pH of acids?
- A. 7.5
- B. < 7
- C. > 7
- D. 7
Correct answer: B
Rationale: The correct answer is B: < 7. Acids have a pH lower than 7, indicating higher acidity. A pH below 7 signifies an acidic solution, with lower values indicating stronger acids. Choice A (7.5) is incorrect as it is greater than 7, which is alkaline. Choice C (> 7) is incorrect as values greater than 7 represent alkaline/basic solutions. Choice D (7) is incorrect because a pH of 7 is neutral, not acidic.
3. 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.
4. What can stop the penetration of beta radiation particles?
- A. Plastic
- B. Glass
- C. Aluminum foil
- D. Concrete
Correct answer: C
Rationale: Beta radiation particles are high-energy, fast-moving electrons or positrons. Aluminum foil is effective in stopping beta radiation due to its ability to absorb and block these particles. When beta particles interact with the aluminum foil, they lose energy and are absorbed, preventing their penetration. Plastic and glass are not as effective as aluminum foil in stopping beta radiation. While concrete provides some shielding against beta particles, aluminum foil is a more suitable material for this purpose as it offers better absorption and blocking capabilities.
5. The three important allotropic forms of phosphorus are red, white, and ___________.
- A. green
- B. gray
- C. black
- D. silver
Correct answer: C
Rationale: The three important allotropic forms of phosphorus are red, white, and black. These forms indicate the different physical properties and reactivity of phosphorus under various conditions. Red phosphorus is more stable and less reactive than white phosphorus, while black phosphorus is the least reactive form. Choice C, 'black,' is the correct answer as it completes the sequence of allotropic forms of phosphorus. Choices A, 'green,' B, 'gray,' and D, 'silver,' are incorrect as they do not represent recognized forms of phosphorus.
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