HESI A2
Chemistry Hesi A2
1. On the periodic table, where are atoms with the largest atomic radius located?
- A. At the top of their group
- B. In the middle of their group
- C. At the bottom of their group
- D. Along the right-hand side
Correct answer: C
Rationale: Atoms with the largest atomic radius are located at the bottom of their group on the periodic table. This is because atomic radius increases down a group due to the addition of more energy levels or shells of electrons. As you move down a group, the outermost electrons are further away from the nucleus, leading to an increase in atomic radius. Choice A 'At the top of their group' is incorrect because atomic radius decreases going up within a group. Choice B 'In the middle of their group' is incorrect as the atomic radius generally increases as you go down a group, not in the middle. Choice D 'Along the right-hand side' is incorrect because atomic radius tends to decrease from left to right across a period on the periodic table due to increased nuclear charge and effective nuclear charge.
2. What creates a dipole in a covalent bond?
- A. Unequal sharing of electrons
- B. Equal sharing of electrons
- C. Exchange of electrons
- D. Transfer of electrons
Correct answer: A
Rationale: A dipole is created in a covalent bond when there is an unequal sharing of electrons between the atoms involved. This results in a partial positive charge on one atom and a partial negative charge on the other, leading to a separation of charges and the formation of a dipole. Choices B, C, and D are incorrect because a dipole is specifically formed due to unequal sharing of electrons, not equal sharing, exchange, or transfer of electrons in a covalent bond.
3. What does a blood sample with a pH of 3 indicate?
- A. It is strongly acidic.
- B. It is strongly basic.
- C. It is weakly acidic.
- D. It is weakly basic.
Correct answer: A
Rationale: A blood pH of 3 is significantly low, indicating a strong acidity level. The normal blood pH range is 7.35 to 7.45; therefore, a pH of 3 is far below the normal range, showing a highly acidic condition in the blood sample. Choice B is incorrect because a pH of 3 is not basic at all. Choice C is incorrect as a pH of 3 is not weakly acidic but strongly acidic. Choice D is wrong as a blood pH of 3 does not indicate a weakly basic condition.
4. Which chemical reaction involves the breaking of a compound into its components?
- A. Decomposition reaction
- B. Combustion reaction
- C. Neutralization reaction
- D. Single displacement reaction
Correct answer: A
Rationale: The correct answer is A: Decomposition reaction. A decomposition reaction involves breaking down a compound into its components. During this reaction, a single compound breaks down into two or more simpler substances. This process is the opposite of a synthesis reaction where multiple substances combine to form a more complex compound. Choices B, C, and D are incorrect because combustion reaction involves burning a substance in oxygen, neutralization reaction involves the reaction between an acid and a base to form water and a salt, and single displacement reaction involves an element displacing another in a compound.
5. Which of the following represents a hydride ion?
- A. Hâ»
- B. Hâº
- C. OHâ»
- D. HCl
Correct answer: A
Rationale: The hydride ion is denoted by Hâ», indicating that it has gained an extra electron to complete its valence shell, resulting in a full octet and a net charge of -1. This ion is commonly found in metal hydrides and plays a significant role in various chemical reactions. Option B, Hâº, represents a proton with a positive charge. Option C, OHâ», represents the hydroxide ion, consisting of oxygen and hydrogen. Option D, HCl, is a compound composed of hydrogen and chlorine ions, not a hydride ion.
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