Q: A sample of iron has a mass of 55.85 g. How many moles of iron are present? (Molar mass of Fe = 55.85 g/mol)

$$\text{Moles} = \dfrac{55.85\ \text{g}}{55.85\ \text{g/mol}} = 1.00$$

Q: A solution is prepared by dissolving 10.0 g of NaCl in enough water to make 250.0 mL of solution. What is the molarity of the solution? (Molar mass of NaCl = 58.44 g/mol)

$$\text{Molarity} = \dfrac{10.0\ \text{g}}{58.44\ \text{g/mol}} \div 0.250\ \text{L} = 0.684\ \text{M}$$

Q: Calculate the energy required to heat 50.0 g of water from 25.0 $$^\circC to 75.0$$ $$^\circC. ($$Specific heat of water $$c = 4.18\ \text{J/g}^\circ\text{C})$$

$$q = m c \Delta T = 50.0\ \text{g} \times 4.18\ \text{J/g}^\circ\text{C} \times (75.0 - 25.0)^\circ\text{C} = 10,450\ \text{J}$$

Question 1

Which of the following statements best describes the difference between a physical and a chemical change? Consider the example of boiling water and burning wood.

Accepted Answer

Boiling water is a physical change because the water remains H$$_2O$$, while burning wood is a chemical change because new substances like CO$$_2$$ and ash are produced.

Question 2

A sample of iron has a mass of 55.85 g. How many moles of iron are present? (Molar mass of Fe = 55.85 g/mol)

Accepted Answer

$$	ext{Moles} = \dfrac{55.85\ 	ext{g}}{55.85\ 	ext{g/mol}} = 1.00$$

Question 3

Which of the following best describes the trend in atomic size across a period from left to right on the periodic table?

Accepted Answer

Atomic size decreases because the increased nuclear charge pulls electrons closer.

Question 4

A solution is prepared by dissolving 10.0 g of NaCl in enough water to make 250.0 mL of solution. What is the molarity of the solution? (Molar mass of NaCl = 58.44 g/mol)

Accepted Answer

$$	ext{Molarity} = \dfrac{10.0\ 	ext{g}}{58.44\ 	ext{g/mol}} \div 0.250\ 	ext{L} = 0.684\ 	ext{M}$$

Question 5

Which of the following is the correct electron configuration for a neutral atom of magnesium (Mg, atomic number 12)?

Accepted Answer

$$1s^2$$\ $$2s^2$$\ $$2p^6$$\ $$3s^2$$

Question 6

Which of the following compounds is named correctly according to IUPAC rules?

Accepted Answer

CO$$_2$$: Carbon dioxide

Question 7

A reaction has an equilibrium constant $$K_c = 1.2 	imes 10$$^{-5}$$. What does this indicate about the reaction at equilibrium?

Accepted Answer

The reaction favors the formation of reactants.

Question 8

Which of the following best describes the effect of increasing temperature on an exothermic reaction at equilibrium, according to Le Châtelier’s Principle?

Accepted Answer

The equilibrium shifts to produce more reactants.

Question 9

Calculate the energy required to heat 50.0 g of water from 25.0 $$^\circC to 75.0$$ $$^\circC. ($$Specific heat of water $$c = 4.18\ 	ext{J/g}^\circ	ext{C})$$

Accepted Answer

$$q = m c \Delta T = 50.0\ 	ext{g} 	imes 4.18\ 	ext{J/g}^\circ	ext{C} 	imes (75.0 - 25.0)^\circ	ext{C} = 10,450\ 	ext{J}$$

Question 10

Which of the following is a correct application of the gas laws? A 2.0 L sample of gas at 1.0 atm and 300 K is compressed to 1.0 L at constant temperature. What is the new pressure?

Accepted Answer

$$P_1$$ $$V_1$$ = $$P_2$$ $$V_2$$ \Rightarrow $$P_2$$ = \dfrac{$$P_1$$ $$V_1$$}{$$V_2$$} = \dfrac{1.0\ 	ext{atm} 	imes 2.0\ 	ext{L}}{1.0\ 	ext{L}} = 2.0\ 	ext{atm}$$

Question 11

Which of the following best describes an electrolyte?

Accepted Answer

A substance that dissolves in water to produce a solution that conducts electricity.

Question 12

Which of the following is the correct calculation for the number of neutrons in an isotope of carbon-14?

Accepted Answer

$$	ext{Neutrons} = 	ext{Mass number} - 	ext{Atomic number} = 14 - 6 = 8$$

Question 13

Which of the following best describes the difference between an ionic and a covalent bond?

Accepted Answer

An ionic bond involves the transfer of electrons from a metal to a nonmetal, while a covalent bond involves the sharing of electrons between nonmetals.

Question 14

A patient’s blood pH is measured at 7.25. Which of the following statements is correct?

Accepted Answer

The blood is slightly acidic, as normal blood pH is about 7.4.

Question 15

Which of the following is the correct scientific notation for the number 0.000345?

Accepted Answer

$$3.45 	imes 10$$^{-4}$$

Question 16

Which of the following is a correct application of OILRIG in redox reactions?

Accepted Answer

Oxidation is loss of electrons; reduction is gain of electrons.

Question 17

Which of the following is true about the boiling point of water at high altitudes?

Accepted Answer

The boiling point decreases because atmospheric pressure is lower.

Question 18

Which of the following is the correct expression for the equilibrium constant $$K_c$$ for the reaction: $$2	ext{NO}_2(g) ightleftharpoons 2	ext{NO}(g) + 	ext{O}_2(g)$$?

Accepted Answer

$$K_c = \dfrac{[	ext{NO}]^2 [	ext{O}_2]}{[	ext{NO}_2]^2}$$

Question 19

Which of the following is a correct temperature conversion from 25 $$^\circC to $$Kelvin?

Accepted Answer

$$T(K) = 25 + 273 = 298\ 	ext{K}$$

Question 20

Which of the following best describes a colloid?

Accepted Answer

A mixture where particles are intermediate in size and do not settle out.

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