Q: Which of the following bases would be best suited to make a buffer solution with a pH of 8.90?

codeine ($$K_b = 1.6 \times 10$$^{-6}$$)

Question 1

Which of the following best describes the relationship between the strength of an acid and its pKa value?

Accepted Answer

A lower pKa value indicates a stronger acid.

Question 2

Given the diagram showing three acids (HX, HY, HZ) and their dissociation in water, which acid has the largest pKa?

Accepted Answer

HY

Question 3

A 0.10 M solution of a weak acid has a pH of 5.44. What is the value of $$K_a$$ for this acid?

$$K_a = \frac{[H_3O^+][A^-]}{[HA]}$$

Accepted Answer

$$1.3 	imes 10$$^{-10}$$

Question 4

Which of the following combinations is a Brønsted-Lowry conjugate acid/base pair?

Accepted Answer

HClO$$_2$$ and ClO$$_2^-$$

Question 5

What is the pH of pure water at 60 $$^\circC$$, given $$K_w = 1.00 	imes 10$$^{-13}$$ at this temperature?

pH$$ = -\log[H_3O^+]$$

Accepted Answer

6.50

Question 6

Which of the following solutions will have the lowest pH?
A. 0.10 M HCN ($$K_a = 6.2 	imes 10$$^{-10}$$)
B. 0.10 M HIO_3$ (K_a = 1.6$$ 	imes $$10^{-1})
C. 0.10 M HF$$ ($$K_a = 6.8 	imes 10$$^{-4}$$)
D. 0.10 M CH_3$CO_2$H (K_a = 1.8$$ 	imes $$10^{-5})
E. 0.10 M $$HNO$$_2$$ ($$K_a = 7.1 	imes 10$$^{-4}$$)

Accepted Answer

0.10 M HIO$$_3$$

Question 7

A buffer solution is prepared by mixing 40.0 mL of 0.15 M HF with 50.0 mL of 0.20 M NaF. ($$K_a = 3.5 	imes 10$$^{-4}$$ for HF) What is the pH of the resulting solution?

Use the Henderson-Hasselbalch equation:

pH = pK_a$$ + \log\left(\frac{[A^-]}{[HA]}ight)$$

Accepted Answer

3.68

Question 8

Which of the following bases would be best suited to make a buffer solution with a pH of 8.90?

Accepted Answer

codeine ($$K_b = 1.6 	imes 10$$^{-6}$$)

Question 9

Which of the following statements is true for the galvanic cell depicted below (Sn/Cu cell)?

Accepted Answer

The mass of the Sn electrode decreases during the reaction

Question 10

For the galvanic cell: Zn(s) $$| Zn$^{2+}(aq$$, 0.010 M) $$|| Ag$^+(aq$$, 0.20 M) $$| Ag(s$$), what is $$E_{cell} at 25.0$$ $$^\circC$$?

Use the Nernst equation:

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

Accepted Answer

1.60 V

Question 11

Which action will make $$E_{cell}$$ more positive for the cell: Cu(s) $$| Cu$^{2+}(aq$$) $$|| Fe$^{3+}(aq$$), Fe$$^{2+}(aq$$) $$| Pt(s$$)?

Accepted Answer

Increasing [Fe$$^{3+}$$]

Question 12

Which of the following salts will give the most basic solution in water?

Accepted Answer

NaOCl

Question 13

Which of the following acids has the strongest conjugate base?
A. HCN
B. HIO$$_3
C. HF
D. CH$_3CO$_2H
E. $$HNO$$_2$$

Accepted Answer

HCN

Question 14

Which of the following statements is true regarding the cell: Zn(s) $$| Zn$^{2+}(aq$$) $$|| Sn$^{2+}(aq$$) $$| Sn(s$$)?

Accepted Answer

The electrons flow from the zinc electrode to the tin electrode

Question 15

What is the percent dissociation of a weak acid if its initial concentration is 1.5 M and its $$K_a = 4.5 	imes 10$$^{-4}$$?

Accepted Answer

1.7%

Question 16

Which component of the carbonic acid/bicarbonate buffer system will react if the pH of blood starts to rise?

Accepted Answer

H$$_2CO$_3$$

Question 17

Balance the following redox reaction in aqueous solution using the smallest whole number coefficients:

$$\mathrm{$$BrO_3$$^- (aq) + N_2H_4 (g) \rightarrow Br^- (aq) + N_2$ (g)}$$

Accepted Answer

$$2\ \mathrm{$$BrO_3$$^-} + 3\ \mathrm{N_2H_4} \rightarrow 2\ \mathrm{Br^-} + 3\ \mathrm{N_2$} + 6\ \mathrm{H_2O}$$

Question 18

Which of the following would have the largest percent ionization?
Pair I: 0.10 M H$$_2Se or 0.10 M H$_2Te
$$Pair II: 0.10 M H$$_2S or 0.20 M H$_2S$$

Accepted Answer

0.10 M H$$_2Te $$and 0.10 M H$$_2S$$

Acids, Bases, and pKa: Comparing Acid Strengths Using Molecular Diagrams

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