Question 1

A sample of an ideal gas occupies 2.50 L at 1.00 atm and 300 K. If the pressure is increased to 2.00 atm and the temperature is raised to 400 K, what will be the new volume of the gas? (Use the ideal gas law: $$PV = nRT)$$

Accepted Answer

$$1.56\ \mathrm{L}$$

Question 2

Which of the following is the correct value and unit for the gas constant $$R$$ when pressure is in $$\mathrm{L\cdot atm}$$ and temperature is in $$\mathrm{K}$$?

Accepted Answer

$$0.08206\ \mathrm{L\cdot atm\cdot $$mol^{-1}$$\cdot K$$^{-1}$$}$$

Question 3

A buffer solution is prepared by mixing $$0.20\ \mathrm{mol} of a $$weak acid (HA) and $$0.10\ \mathrm{mol} of $$its conjugate base (A$$^-) in$$ $$1.0\ \mathrm{L} of $$solution. If the $$K_a of $$the acid is $$1.0 	imes 10$$^{-5}$$, what is the pH of the solution? (Use pH$$ = -\log K_a + \log \left( \frac{[base]}{[acid]} ight)$$)

Accepted Answer

$$4.00 - 0.30 = 3.70$$

Question 4

Which of the following statements about the periodic table is correct?

Accepted Answer

Elements in the same group have similar chemical properties because they have the same number of valence electrons.

Question 5

A reaction vessel contains $$2.0\ \mathrm{mol} of$$ $$\mathrm{H_2$}$$, $$1.0\ \mathrm{mol} of$$ $$\mathrm{N_2$}$$, and $$3.0\ \mathrm{mol} of$$ $$\mathrm{NH_3$} at $$equilibrium. The balanced equation is $$\mathrm{N_2$} + 3\mathrm{H_2$} \rightleftharpoons 2\mathrm{NH_3$}. $$What is the expression for the equilibrium constant $$K_c$$ for this reaction?

Accepted Answer

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

Question 6

A $$0.10\ \mathrm{M}$$ solution of a weak acid has a pH of $$3.00. $$What is the $$K_a of $$the acid? (Use $$[H^+] = 10$$^{-pH}$$ and K_a$$ = \frac{[H^+]^2}{[HA] - [H^+]}$$)

Accepted Answer

$$1.0 	imes 10$$^{-4}$$

Question 7

Which of the following best explains why noble gases are generally unreactive?

Accepted Answer

They have completely filled valence electron shells.

Question 8

A sample of gas is collected over water at $$25^\circ\mathrm{C}$$ and a total pressure of $$760\ \mathrm{mmHg}. $$The vapor pressure of water at this temperature is $$24\ \mathrm{mmHg}. $$What is the partial pressure of the dry gas?

Accepted Answer

$$736\ \mathrm{mmHg}$$

Question 9

Which of the following is the correct relationship for calculating the pH of a buffer solution?

Accepted Answer

$$pH = -\log K_a + \log \left( \frac{[base]}{[acid]} \right)$$

Question 10

Which of the following units is NOT a valid unit for the gas constant $$R$$?

Accepted Answer

$$1.987\ \mathrm{mol\cdot K\cdot L$$^{-1}$$}$$

Question 11

A medical oxygen tank contains $$10.0\ \mathrm{L} of$$ $$O_2$$ gas at $$25^\circ\mathrm{C}$$ and $$150\ \mathrm{atm}. $$How many moles of $$O_2$$ are present? (Use $$R = 0.08206\ \mathrm{L\cdot atm\cdot $$mol^{-1}$$\cdot K$$^{-1}$$})$$

Accepted Answer

$$61.0\ \mathrm{mol}$$

Question 12

Which of the following best describes the trend in ionization energy across a period in the periodic table?

Accepted Answer

Ionization energy increases from left to right across a period.

Question 13

A $$0.50\ \mathrm{mol}$$ sample of an ideal gas is at $$300\ \mathrm{K}$$ and $$2.00\ \mathrm{atm}. $$What is the volume of the gas? (Use $$R = 0.08206\ \mathrm{L\cdot atm\cdot $$mol^{-1}$$\cdot K$$^{-1}$$})$$

Accepted Answer

$$6.15\ \mathrm{L}$$

Question 14

Which of the following is a correct statement about the relationship between $$K_a$$ and acid strength?

Accepted Answer

A larger $$K_a$$ value indicates a stronger acid.

Question 15

A student prepares a buffer by mixing $$0.30\ \mathrm{mol} of $$acetic acid and $$0.30\ \mathrm{mol} of $$sodium acetate in $$1.0\ \mathrm{L} of $$water. If the $$K_a of $$acetic acid is $$1.8 	imes 10$$^{-5}$$, what is the pH of the buffer?

Accepted Answer

$$4.74$$

Question 16

Which of the following best explains why the vapor pressure of water increases with temperature?

Accepted Answer

As temperature increases, more water molecules have enough kinetic energy to escape into the vapor phase.

Question 17

Which of the following is the correct formula for calculating the number of moles of a gas using the ideal gas law?

Accepted Answer

$$n = \frac{PV}{RT}$$

Question 18

A $$1.0\ \mathrm{L}$$ solution contains $$0.10\ \mathrm{mol} of a $$weak base and $$0.10\ \mathrm{mol} of $$its conjugate acid. If the $$K_b of $$the base is $$1.0 	imes 10$$^{-5}$$, what is the pOH of the solution? (Use $$pOH = -\log K_b$$)

Accepted Answer

$$5.00$$

Question 19

Which of the following best describes the trend in atomic radius down a group in the periodic table?

Accepted Answer

Atomic radius increases down a group.

Essential Reference Data and Concepts for General Chemistry Exams

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