how many neutrons does carbon 14 have

HESI A2

Chemistry HESI A2 Practice Test

1. How many neutrons does carbon-14 have?

A. 10
B. 8
C. 6
D. 12

Correct answer: B

Rationale: The correct answer is B: 8. Carbon-14 is an isotope of carbon with 6 protons and 8 neutrons. To determine the number of neutrons in an atom, subtract the atomic number (number of protons) from the mass number. In this case, the mass number of carbon-14 is 14, and the atomic number of carbon is 6. Therefore, 14 (mass number) - 6 (atomic number) = 8 neutrons. Choices A, C, and D are incorrect because they do not reflect the correct number of neutrons in a carbon-14 atom.

2. If oxygen is in a compound, what would its oxidation number be?

A. 2
B. -2
C. 0
D. -1

Correct answer: B

Rationale: Oxygen typically has an oxidation number of -2 in compounds because it tends to gain electrons. This is due to its high electronegativity, which leads to oxygen attracting electrons towards itself in a chemical bond. Choice A (2) is incorrect because oxygen doesn't have a +2 oxidation number in compounds. Choice C (0) is incorrect as oxygen rarely has an oxidation number of 0 in compounds. Choice D (-1) is incorrect as oxygen's oxidation number in compounds is typically -2, not -1.

3. What is the oxidation state of the nitrogen atom in the compound NH3?

A. -3
B. -1
C. +1
D. +3

Correct answer: B

Rationale: In the compound NH3, nitrogen is bonded to three hydrogen atoms. Hydrogen is always assigned an oxidation state of +1. Since the overall charge of NH3 is zero, the oxidation state of nitrogen must be -1 to balance out the hydrogen's +1 oxidation state. Therefore, the correct oxidation state of the nitrogen atom in NH3 is -1. Choice A (-3) is incorrect because it does not account for the electronegativity of hydrogen. Choice C (+1) and Choice D (+3) are incorrect as the nitrogen atom in NH3 needs to balance the +1 oxidation state of each hydrogen atom, resulting in a total of -3 to maintain the compound's charge neutrality.

4. How many amino acids are essential for human life?

A. 22
B. 20
C. 18
D. 24

Correct answer: B

Rationale: There are 20 essential amino acids required for human life. These amino acids cannot be synthesized by the body and must be obtained through the diet. They play crucial roles in various physiological functions and are necessary for protein synthesis and overall health. Choice A is incorrect because there are not 22 essential amino acids. Choice C is incorrect as there are more than 18 essential amino acids. Choice D is incorrect as there are not 24 essential amino acids for human life.

5. Where would you expect tap water to fall on the pH scale?

A. Between 1 and 3
B. Between 4 and 6
C. Between 6 and 8
D. Between 8 and 10

Correct answer: C

Rationale: Tap water typically falls within the pH range of 6 to 8, making it slightly acidic to neutral. Most municipal water systems aim to provide water that is safe for consumption and falls within this pH range. A pH level of 7 is considered neutral, so tap water may vary slightly on either side of this number but typically remains within the 6 to 8 range to ensure it is safe for consumption. Choices A, B, and D are incorrect because tap water is not expected to have a pH as low as 1-3 (highly acidic) or as high as 8-10 (alkaline); it usually falls within the slightly acidic to neutral range, hence falling between 6 and 8 on the pH scale.