Question 1

Which of the following statements about the ion-product constant for water ($$K_w) at 25$$ $$^\circC is $$correct?

Accepted Answer

$$K_w = [\mathrm{H_3O^+}][\mathrm{OH^-}]$$

Question 2

A solution is prepared by mixing 0.10 M acetic acid ($$\mathrm{CH_3COOH}$$, $$K_a = 1.8 	imes 10$$^{-5}$$) and 0.10 M sodium acetate ($$\mathrm{CH_3COONa}$$). Which statement best describes this solution?

Accepted Answer

It is a buffer solution that resists changes in pH upon addition of small amounts of acid or base.

Question 3

Which of the following salts will produce a basic solution when dissolved in water?

Accepted Answer

Sodium acetate ($$\mathrm{CH_3COONa})$$

Question 4

Calculate the pH of a 0.250 M solution of a weak acid with $$K_a = 1.5 	imes 10$$^{-5}$$.

Accepted Answer

$$3.12$$

Question 5

Which of the following processes is accompanied by an increase in entropy ($$\Delta S \u003e 0$$)?

Accepted Answer

Sublimation of dry ice: $$\mathrm{CO_2$ (s) \rightarrow CO_2$ (g)}$$

Question 6

Which of the following statements is true regarding the spontaneity of a reaction with $$\Delta H \u003e 0$$ and $$\Delta S \u003c 0$$?

Accepted Answer

The reaction is nonspontaneous at any temperature.

Question 7

Given the following standard entropies: $$S^\circ(\mathrm{Al (s)}) = 28.3 J/$$mol·K, $$S^\circ(\mathrm{$$MnO_2$$ (s)}) = 32.0 J/$$mol·K, $$S^\circ(\mathrm{Al_2O_3 (s)}) = 50.9 J/$$mol·K, $$S^\circ(\mathrm{Mn (s)}) = 53.1 J/$$mol·K, calculate $$\Delta S^\circ$$ for the reaction: $$4\mathrm{Al (s)} + 3\mathrm{$$MnO_2$$ (s)} \rightarrow 2\mathrm{Al_2O_3 (s)} + 3\mathrm{Mn (s)}.$$

Accepted Answer

$$-51.9 J/$$mol·K

Question 8

Which of the following best describes the function of a salt bridge in a galvanic cell?

Accepted Answer

It maintains electrical neutrality by allowing the flow of ions between the half-cells.

Question 9

A buffer is prepared by mixing 0.20 mol of formic acid ($$pK_a = 3.75) $$and 0.10 mol of sodium formate in enough water to make 1.0 L of solution. What is the pH of the buffer?

Accepted Answer

$$3.45$$

Question 10

Which of the following changes will increase the cell potential ($$E_{cell}) of a $$galvanic cell?

Accepted Answer

Increasing the concentration of ions in the cathode half-cell.

Question 11

Which of the following is the correct relationship between the equilibrium constant $$K$$ and the standard free energy change $$\Delta G^\circ$$?

Accepted Answer

$$\Delta G^\circ = -RT \ln K$$

Question 12

A student titrates 25.0 mL of 0.100 M acetic acid ($$K_a = 1.8 	imes 10$$^{-5}$$) with 0.100 M NaOH. What is the pH at the equivalence point?

Accepted Answer

$$8.72$$

Question 13

Which of the following best describes an amphiprotic substance?

Accepted Answer

A substance that can act as either an acid or a base.

Question 14

Which of the following is the strongest acid?

Accepted Answer

Formic acid ($$pK_a = 3.75)$$

Question 15

At what temperature is the entropy of a perfect crystal exactly zero, according to the third law of thermodynamics?

Accepted Answer

$$0\ \mathrm{K}$$

Question 16

Which of the following is the correct cell notation for a galvanic cell with zinc as the anode and copper as the cathode?

Accepted Answer

$$| \mathrm{Zn (s)} | \mathrm{Zn$$^{2+}$$ (aq)} || \mathrm{Cu$$^{2+}$$ (aq)} | \mathrm{Cu (s)} |$$

Question 17

Which of the following best explains why the value of $$K_w$$ increases as temperature increases?

Accepted Answer

The autoionization of water is endothermic, so increasing temperature shifts the equilibrium to produce more ions.

Question 18

Which of the following is the correct Nernst equation for a cell reaction involving $$n$$ electrons?

Accepted Answer

$$E = E^\circ - \frac{0.0592}{n} \log Q$$

Question 19

A reaction has $$\Delta H = -100 kJ $$and $$\Delta S = -200 J/K. At $$what temperature (in K) does the reaction change from spontaneous to nonspontaneous?

Accepted Answer

$$500 K$$

CHE 104 General Chemistry II Exam 3A – Guided Study Notes

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