HESI A2
HESI A2 Chemistry
1. Which of these elements has the greatest atomic mass?
- A. Au
- B. Ba
- C. I
- D. W
Correct answer: D
Rationale: Among the elements listed, Tungsten (W) has the greatest atomic mass. The atomic mass of Tungsten is approximately 183.84 atomic mass units (amu), while the atomic masses of the other elements listed are as follows: Gold (Au) is around 196.97 amu, Barium (Ba) is approximately 137.33 amu, and Iodine (I) is about 126.90 amu. Therefore, Tungsten (W) has the greatest atomic mass out of the given elements. Gold (Au) has a higher atomic mass than Barium (Ba) and Iodine (I), making choices A, B, and C incorrect.
2. Which of the following is a characteristic property of acids?
- A. Sour taste
- B. Bitter taste
- C. Reacts with bases
- D. Slippery feel
Correct answer: A
Rationale: The correct answer is 'A: Sour taste.' Acids are known to have a sour taste, which is a fundamental characteristic property of acids. This taste distinguishes acids from bases, which are more likely to have a bitter taste. The sour taste of acids is due to the presence of hydrogen ions in them. Therefore, when identifying an acid based on taste, the sour taste serves as a key indicator. Choices B, C, and D are incorrect. Bitter taste is associated with bases, not acids. While acids do react with bases (Choice C), this is not a characteristic property of acids but rather a chemical behavior. Slippery feel (Choice D) is a property of bases, not acids.
3. What are the two types of chemical bonding?
- A. Covalent & hydrogen
- B. Ionic & covalent
- C. Ionic & hydrogen
- D. Covalent & metallic
Correct answer: B
Rationale: The correct answer is B: Ionic & covalent. Ionic bonding involves the transfer of electrons between atoms, resulting in the formation of positive and negative ions attracted to each other. Covalent bonding involves the sharing of electrons between atoms to achieve a stable electron configuration. Choice A is incorrect as hydrogen bonding is a type of intermolecular force, not a primary type of chemical bonding. Choice C is incorrect as hydrogen bonding is not a primary type of chemical bonding. Choice D is incorrect as metallic bonding involves the sharing of electrons in a 'sea of electrons' within a metal lattice, not covalent bonding.
4. The molar mass of some gases is as follows: carbon monoxide—28.01 g/mol; helium—4.00 g/mol; nitrogen—28.01 g/mol; and oxygen—32.00 g/mol. Which would you expect to diffuse most rapidly?
- A. Carbon monoxide
- B. Helium
- C. Nitrogen
- D. Oxygen
Correct answer: B
Rationale: The rate of diffusion is inversely proportional to the molar mass of the gas. Helium has the lowest molar mass among the given gases, making it the lightest and fastest gas to diffuse. Therefore, helium would be expected to diffuse most rapidly compared to carbon monoxide, nitrogen, and oxygen. Carbon monoxide, nitrogen, and oxygen have higher molar masses than helium, so they would diffuse more slowly. Therefore, the correct answer is helium.
5. What type of intermolecular force is a dipole attraction?
- A. Strong
- B. Weak
- C. Medium
- D. Very strong
Correct answer: B
Rationale: A dipole attraction is considered a weak intermolecular force. It occurs between molecules with permanent dipoles, where the positive end of one molecule is attracted to the negative end of another molecule. While dipole-dipole interactions are stronger than dispersion forces, they are weaker than hydrogen bonding or ion-dipole interactions. Therefore, the correct answer is 'Weak.' Choices A, C, and D are incorrect because dipole attractions are not classified as strong, medium, or very strong intermolecular forces, but rather fall into the category of weak intermolecular forces.
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