Q: What is the pH of a 0.010 M solution of HCl, a strong acid, at 25$$^ ext{o}C$$?

$$\text{pH} = -\log(0.010) = 2.00$$

Q: The autoionization of water can be represented by which of the following equations?

$$2\ \text{H}_2\text{O} \rightleftharpoons \text{H}_3\text{O}^+ + \text{OH}^-$$

Q: A buffer solution is prepared by mixing 0.50 M acetic acid (CH$$_3$$COOH) and 0.50 M sodium acetate (CH$$_3$$COONa). If the $$\text{p}K_a of $$acetic acid is 4.76, what is the pH of the buffer?

$$\text{pH} = \text{p}K_a + \log\left(\frac{[\text{base}]}{[\text{acid}]}\right) = 4.76 + \log(1) = 4.76$$

Q: Calculate the percent ionization of a 0.10 M solution of a weak acid with $$K_a = 1.8 \times 10$$^{-5}$$.

Percent ionization $$= \frac{\sqrt{K_a \cdot [\text{acid}]}}{[\text{acid}]} \times 100\% = \frac{\sqrt{1.8 \times 10$$^{-5}$$ \cdot 0.10}}{0.10} \times 100\% \approx 1.34\%$$

Question 1

Which of the following statements best describes a Bronsted-Lowry acid?

Accepted Answer

A substance that donates a proton (H$$^+) to $$another species.

Question 2

What is the pH of a 0.010 M solution of HCl, a strong acid, at 25$$^	ext{o}C$$?

Accepted Answer

$$	ext{pH} = -\log(0.010) = 2.00$$

Question 3

Which of the following pairs are conjugate acid-base pairs?

Accepted Answer

NH$$_3$$ and NH$$_4^+$$

Question 4

The autoionization of water can be represented by which of the following equations?

Accepted Answer

$$2\ 	ext{H}_2	ext{O} ightleftharpoons 	ext{H}_3	ext{O}^+ + 	ext{OH}^-$$

Question 5

A buffer solution is prepared by mixing 0.50 M acetic acid (CH$$_3$$COOH) and 0.50 M sodium acetate (CH$$_3$$COONa). If the $$	ext{p}K_a of $$acetic acid is 4.76, what is the pH of the buffer?

Accepted Answer

$$	ext{pH} = 	ext{p}K_a + \log\left(\frac{[	ext{base}]}{[	ext{acid}]}ight) = 4.76 + \log(1) = 4.76$$

Question 6

Which salt solution will be basic in water?

Accepted Answer

NaF

Question 7

Calculate the percent ionization of a 0.10 M solution of a weak acid with $$K_a = 1.8 	imes 10$$^{-5}$$.

Accepted Answer

Percent ionization $$= \frac{\sqrt{K_a \cdot [	ext{acid}]}}{[	ext{acid}]} 	imes 100\% = \frac{\sqrt{1.8 	imes 10$$^{-5}$$ \cdot 0.10}}{0.10} 	imes 100\% \approx 1.34\%$$

Question 8

Which of the following statements about entropy ($$S) is $$correct?

Accepted Answer

Entropy is a measure of the disorder or randomness of a system.

Question 9

Which process will have a positive $$\Delta S$$?

Accepted Answer

Melting of ice to liquid water.

Question 10

A reaction has $$\Delta H = -100\ 	ext{kJ}$$ and $$\Delta S = -200\ 	ext{J/K}. At $$what temperature will the reaction change from spontaneous to nonspontaneous?

Accepted Answer

$$T = \frac{\Delta H}{\Delta S} = \frac{-100\$$times10^3$$}{-200} = 500\ 	ext{K}$$

Question 11

Which equation correctly relates the Gibbs free energy change to enthalpy and entropy?

Accepted Answer

$$\Delta G = \Delta H - T\Delta S$$

Question 12

A reaction at equilibrium has which value for $$\Delta G$$?

Accepted Answer

$$\Delta G = 0$$

Question 13

Which of the following is true about the relationship between the strength of an acid and its conjugate base?

Accepted Answer

The stronger the acid, the weaker its conjugate base.

Question 14

Given $$K_a$$ for an acid is $$1.0 	imes 10$$^{-5}$$, what is the K_b$ for its conjugate base at 25$$^	ext{o}$$C?

Accepted Answer

$$K_b = \frac{K_w}{K_a} = \frac{1.0 	imes 10$$^{-14}$$}{1.0 	imes 10$$^{-5}$$} = 1.0 	imes 10$$^{-9}$$

Question 15

During a titration of a weak acid with a strong base, what is the pH at the halfway point to the equivalence point?

Accepted Answer

$$	ext{pH} = 	ext{p}K_a$$

Question 16

Which of the following best describes the effect of adding a common ion to a solution at equilibrium?

Accepted Answer

It shifts the equilibrium to reduce the concentration of the ion added.

Question 17

Calculate the pH of a 0.020 M NaOH solution at 25$$^	ext{o}C.$$

Accepted Answer

$$	ext{pOH} = -\log(0.020) = 1.70$$; $$	ext{pH} = 14.00 - 1.70 = 12.30$$

Question 18

Which statement about the second law of thermodynamics is correct?

Accepted Answer

The entropy of the universe always increases in a spontaneous process.

Question 19

A reaction has $$\Delta G^\circ = -40\ 	ext{kJ} at 298 K. $$What is the equilibrium constant $$K$$ for the reaction?

Accepted Answer

$$\Delta G^\circ = -RT \ln K \Rightarrow K = e$$^{-\Delta G^\circ/(RT)}$$ = e$$^{40,000/(8.314 	imes 298)}$$ \approx 1.6 	imes 10^7$

Question 20

Which of the following is a real-life example of a spontaneous process?

Accepted Answer

NaCl dissolving in water.

Aqueous Equilibrium and Thermodynamics: Study Guide for CHEM 104 Exam 3

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