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. Which compound is a Hydrogen or proton donor, corrosive to metals, causes blue litmus paper to become red, and becomes less acidic when mixed with a base?

A. Base
B. Acid
C. Salt
D. Hydroxide

Correct answer: B

Rationale: The correct answer is 'Acid.' An acid is a compound that donates protons (H+), is corrosive to metals, and turns blue litmus paper red. When an acid is mixed with a base, they react to form salts and water, resulting in a decrease in acidity. Choices A, C, and D are incorrect because bases accept protons rather than donate them, salts are the products of acid-base reactions, and hydroxides are typically bases, not acids.

3. Which substance forms hydroxide ions when placed in water?

A. Lemon juice
B. Battery acid
C. Vinegar
D. Lye

Correct answer: D

Rationale: The correct answer is D, lye. Lye, also known as sodium hydroxide (NaOH), is a strong base that forms hydroxide ions (OH-) when placed in water. When lye dissolves in water, it dissociates into sodium ions (Na+) and hydroxide ions, making it an alkaline substance. Lemon juice, battery acid, and vinegar do not form hydroxide ions when placed in water. Lemon juice contains citric acid, battery acid contains sulfuric acid, and vinegar contains acetic acid, none of which produce hydroxide ions when dissolved in water.

4. Which is a property of an ionic compound?

A. Low melting point
B. Poor conductivity
C. Shared electrons
D. Crystalline shape

Correct answer: D

Rationale: Ionic compounds are composed of positively and negatively charged ions that are held together by strong electrostatic forces. These ions arrange themselves in a repeating pattern to form a stable and orderly structure known as a crystalline shape. This is a characteristic property of ionic compounds, making choice D the correct answer. Choices A, B, and C are incorrect because ionic compounds typically have high melting points, good conductivity in the molten or dissolved state, and do not involve shared electrons but rather the transfer of electrons between atoms.

5. How can the reaction rate of a chemical reaction be increased?

A. Increase the temperature
B. Increase the surface area
C. Increase the concentration of reactants
D. Add a catalyst

Correct answer: A

Rationale: To increase the reaction rate of a chemical reaction, one effective method is to increase the temperature. Raising the temperature provides more energy to the reacting particles, enabling them to collide more frequently and with higher energy, leading to an increase in the reaction rate. While increasing the surface area, concentration of reactants, and adding a catalyst are strategies that can also enhance the reaction rate, raising the temperature has the most direct and immediate impact. Increasing the surface area allows for more contact between reactants, increasing the concentration provides more reactant particles to collide, and adding a catalyst lowers the activation energy required for the reaction to occur. However, these methods may not have as immediate and significant an effect as increasing the temperature.