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)

$$M = \frac{\text{moles}}{\text{liters}} = \frac{10.0\ \mathrm{g} / 58.44\ \mathrm{g/mol}}{0.250\ \mathrm{L}} = 0.684\ \mathrm{M}$$

Q: A sample of water is heated from $$25^\circ \mathrm{C} to$$ $$75^\circ \mathrm{C}. If $$the mass of water is 100.0 g and the specific heat capacity is $$4.18\ \mathrm{J/g\cdot ^\circ C}$$, how much heat is absorbed?

$$q = m c \Delta T = 100.0\ \mathrm{g} \times 4.18\ \mathrm{J/g\cdot ^\circ C} \times (75 - 25)\ ^\circ \mathrm{C} = 20,900\ \mathrm{J}$$

Q: How many molecules are present in 0.250 mol of $$\mathrm{CO_2$}$$? (Avogadro's number $$= 6.022 \times 10$$^{23}$$ molecules/mol)

$$0.250\ \mathrm{mol} \times 6.022 \times 10$$^{23}$$\ \mathrm{molecules/mol} = 1.51 \times 10$$^{23}$$\ \mathrm{molecules}$$

Q: A 20.0 g sample of a radioactive isotope decays to 2.5 g in 24 hours. What is the half-life of the isotope?

$$\text{Number of half-lives} = \log_2$\left(\frac{20.0}{2.5}\right) = 3$$; $$\text{Half-life} = \frac{24\ \mathrm{h}}{3} = 8.0\ \mathrm{h}$$

Question 1

A sample of a metal has a mass of 45.0 g and a volume of 15.0 mL. What is the density of the metal?

Accepted Answer

$$d = \frac{m}{V} = \frac{45.0\ \mathrm{g}}{15.0\ \mathrm{mL}} = 3.00\ \mathrm{g/mL}$$

Question 2

Which of the following changes is a chemical change?

Accepted Answer

Burning of wood

Question 3

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

$$M = \frac{	ext{moles}}{	ext{liters}} = \frac{10.0\ \mathrm{g} / 58.44\ \mathrm{g/mol}}{0.250\ \mathrm{L}} = 0.684\ \mathrm{M}$$

Question 4

Which of the following statements about isotopes is correct?

Accepted Answer

Isotopes of an element have the same number of protons but different numbers of neutrons.

Question 5

A sample of water is heated from $$25^\circ \mathrm{C} to$$ $$75^\circ \mathrm{C}. If $$the mass of water is 100.0 g and the specific heat capacity is $$4.18\ \mathrm{J/g\cdot ^\circ C}$$, how much heat is absorbed?

Accepted Answer

$$q = m c \Delta T = 100.0\ \mathrm{g} 	imes 4.18\ \mathrm{J/g\cdot ^\circ C} 	imes (75 - 25)\ ^\circ \mathrm{C} = 20,900\ \mathrm{J}$$

Question 6

Which of the following compounds is named correctly?

Accepted Answer

NaCl: sodium chloride

Question 7

How many molecules are present in 0.250 mol of $$\mathrm{CO_2$}$$? (Avogadro's number $$= 6.022 	imes 10$$^{23}$$ molecules/mol)

Accepted Answer

$$0.250\ \mathrm{mol} 	imes 6.022 	imes 10$$^{23}$$\ \mathrm{molecules/mol} = 1.51 	imes 10$$^{23}$$\ \mathrm{molecules}$$

Question 8

Which of the following best describes an exothermic process?

Accepted Answer

A process in which heat is released to the surroundings and $$\Delta H is $$negative.

Question 9

Which of the following is the correct electron configuration for a neutral atom of magnesium ($$Z=12$$)?

Accepted Answer

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

Question 10

A 20.0 g sample of a radioactive isotope decays to 2.5 g in 24 hours. What is the half-life of the isotope?

Accepted Answer

$$	ext{Number of half-lives} = \log_2$\left(\frac{20.0}{2.5}ight) = 3$$; $$	ext{Half-life} = \frac{24\ \mathrm{h}}{3} = 8.0\ \mathrm{h}$$

Question 11

Which of the following solutions will have the lowest freezing point? Assume all solutions are made with 1.0 mol of solute in 1.0 kg of water.

Accepted Answer

$$\mathrm{Na_2SO_4} ($$dissociates into 3 ions)

Question 12

Which of the following is the correct net ionic equation for the reaction between aqueous solutions of $$\mathrm{Na_2SO_4}$$ and $$\mathrm{$$BaCl_2$$}$$?

Accepted Answer

$$\mathrm{Ba$$^{2+}$$ (aq) + SO_4$^{2-} (aq) \rightarrow $$BaSO_4$$ (s)}$$

Question 13

Which of the following molecules is polar?

Accepted Answer

$$\mathrm{H_2O}$$

Question 14

A gas occupies 2.00 L at 1.00 atm. If the pressure is increased to 4.00 atm at constant temperature, what is the new volume?

Accepted Answer

$$P_1V_1 = P_2V_2 \Rightarrow V_2$ = \frac{P_1V_1}{P_2$} = \frac{1.00\ \mathrm{atm} 	imes 2.00\ \mathrm{L}}{4.00\ \mathrm{atm}} = 0.500\ \mathrm{L}$$

Question 15

Which of the following is a correct statement about intermolecular forces?

Accepted Answer

Hydrogen bonding is a special type of dipole-dipole interaction that occurs when hydrogen is bonded to N, O, or F.

Question 16

Which of the following is the correct expression for the equilibrium constant $$K_c$$ for the reaction: $$\mathrm{N_2$ (g) + 3H_2 (g) \rightleftharpoons 2NH_3 (g)}$$?

Accepted Answer

$$K_c = \frac{[NH_3$]^2}{[N_2$][H_2$]^3}$$

Question 17

A solution has a pH of 3.0. What is the concentration of hydronium ions $$[H_3O^+] in $$the solution?

Accepted Answer

$$[H_3O^+] = 10$$^{-3.0}$$\ \mathrm{M} = 1.0 	imes 10$$^{-3}$$\ \mathrm{M}$$

Question 18

Which of the following is a buffer solution?

Accepted Answer

A solution containing acetic acid and sodium acetate

Question 19

Which of the following is the correct symbol for a beta particle in nuclear decay?

Accepted Answer

$$^0_{-1}e$$

ACS Final Exam Review: Comprehensive Study Guide for Introductory Chemistry

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