Q: A voltaic cell is constructed with two $$\mathrm{Zn$$^{2+}$$/Zn}$$ electrodes. The two cell compartments have $$[\mathrm{Zn$$^{2+}$$}] = 5.00 M $$and $$[\mathrm{Zn$$^{2+}$$}] = 1.00 \times 10$$^{-2}$$ M, respectively. Which electrode is the anode?

The electrode with $$[\mathrm{Zn$$^{2+}$$}] = 1.00 \times 10$$^{-2}$$ M

Question 1

Which of the following statements best explains why $$\mathrm{$$HClO_4$$} is a $$stronger acid than $$\mathrm{$$HClO_3$$}$$, $$\mathrm{$$HClO_2$$}$$, and $$\mathrm{HClO}$$?

Accepted Answer

Because $$\mathrm{$$HClO_4$$}$$ has more oxygen atoms, which stabilize the negative charge on the conjugate base through resonance.

Question 2

A 0.1 M solution of which of the following salts will produce the most basic solution?

Accepted Answer

KCN, because cyanide is the conjugate base of a very weak acid.

Question 3

Which of the following aqueous solutions has the highest $$[\mathrm{OH^-}]$$ concentration?

Accepted Answer

Pure water

Question 4

Calculate the pH of a 0.10 M aqueous solution of sodium formate ($$\mathrm{$$NaHCO_2$$}$$), given $$K_a$$ for formic acid is $$1.8 	imes 10$$^{-4}$$.

Accepted Answer

$$8.37$$

Question 5

Which of the following pairs cannot be mixed together to form a buffer solution?

Accepted Answer

$$\mathrm{KOH}$$, $$\mathrm{HI}$$

Question 6

When the concentrations of a weak acid and its conjugate base are equal in a solution, which of the following is true?

Accepted Answer

The $$-\log[\mathrm{H^+}]$$ and the $$-\log K_a$$ are equal.

Question 7

Which combination will NOT produce a buffer solution when added to water?

Accepted Answer

None of the above

Question 8

Given the following $$K_{sp}$$ values, which compound has the greatest molar solubility in water?

$$\mathrm{$$CdCO_3$$}$$: $$5.2 	imes 10$$^{-12}$$
$$\mathrm{Cd(OH)_2}$$: 2.5$$ 	imes $$10^{-14}$$
$$\mathrm{$$CaF_2$$}$$: $$3.9 	imes 10$$^{-11}$$
$$\mathrm{AgI}$$: 8.3$$ 	imes $$10^{-17}$$
$$\mathrm{$$ZnCO_3$$}$$: $$1.4 	imes 10$$^{-11}$$

Accepted Answer

$$\mathrm{$$CaF_2$$}$$

Question 9

In which of the following aqueous solutions would you expect $$\mathrm{CuBr} to $$have the highest solubility?

Accepted Answer

Pure water

Question 10

A 25.0-mL sample of 0.150 M butanoic acid is titrated with a 0.150 M NaOH solution. What is the pH before any base is added? ($$K_a of $$butanoic acid is $$1.5 	imes 10$$^{-5}$$)

Accepted Answer

$$2.83$$

Question 11

A solution of NaF is added dropwise to a solution that is 0.0144 M in $$\mathrm{Ba$$^{2+}$$}. $$When the concentration of $$\mathrm{F^-}$$ exceeds __________ M, $$\mathrm{$$BaF_2$$}$$ will precipitate. ($$K_{sp}$$ for $$\mathrm{$$BaF_2$$} is$$ $$1.7 	imes 10$$^{-6}$$)

Accepted Answer

$$1.1 	imes 10$$^{-2}$$

Question 12

Which element is oxidized in the reaction below?

$$\mathrm{Fe$$^{2+}$$ + H^+ + Cr_2O_7$$^{2-}$$ \rightarrow Fe$$^{3+}$$ + Cr$$^{3+}$$ + H_2O}$$

Accepted Answer

Fe

Question 13

Which of the halogens in the provided table is the strongest oxidizing agent?

Accepted Answer

$$\mathrm{F_2$}$$

Question 14

What is the coefficient of the permanganate ion when the following equation is balanced in acidic solution?

$$\mathrm{$$MnO_4$$^- + Br^- \rightarrow Mn$$^{2+}$$ + Br_2$}$$

Accepted Answer

2

Question 15

The standard cell potential ($$E^\circ_{cell}) $$for the reaction below is $$+0.63 V. $$What is the cell potential when $$[\mathrm{Zn$$^{2+}$$}] = 3.5 M $$and $$[\mathrm{Pb$$^{2+}$$}] = 2.0 	imes 10$$^{-4}$$ M?

$$\mathrm{$$Pb^{2+} (aq) + Zn (s$$) ightarrow $$Zn^{2+} (aq) + Pb (s$$)}$$

Accepted Answer

$$0.50 V$$

Question 16

Calculate the pH of a 0.10 M aqueous pyridine ($$\mathrm{C_5H_5N}) $$solution. ($$K_b = 1.7 	imes 10$$^{-9}$$)

Accepted Answer

$$9.11$$

Question 17

A 35.0 mL sample of 0.200 M benzoic acid ($$\mathrm{HC_7H_5O_2}$$, $$K_a = 6.4 	imes 10$$^{-5}$$) is titrated with 0.100 M NaOH solution. What is the pH after the addition of 30.0 mL of NaOH?

Accepted Answer

$$4.07$$

Question 18

The solubility of $$\mathrm{$$PbCl_2$$} is$$ $$4.45 g/L. $$What is the $$K_{sp} of$$ $$\mathrm{$$PbCl_2$$}$$? (Molar mass $$= 278.1 g/$$mol)

Accepted Answer

$$1.58 	imes 10$$^{-5}$$

Question 19

A solution contains $$0.15 M$$ $$\mathrm{Mg$$^{2+}$$}$$ and $$0.12 M$$ $$\mathrm{Zn$$^{2+}$$}. $$Given $$K_{sp}$$ for $$\mathrm{Mg(OH)_2} is$$ $$1.6 	imes 10$$^{-12}$$ and for $$\mathrm{Zn(OH)_2}$$ is 3.0$$ 	imes $$10^{-16}$$, at what pH range can you separate these two ions by selective precipitation?

Accepted Answer

$$6.70 - 8.51$$

Question 20

A voltaic cell is constructed with two $$\mathrm{Zn$$^{2+}$$/Zn}$$ electrodes. The two cell compartments have $$[\mathrm{Zn$$^{2+}$$}] = 5.00 M $$and $$[\mathrm{Zn$$^{2+}$$}] = 1.00 	imes 10$$^{-2}$$ M, respectively. Which electrode is the anode?

Accepted Answer

The electrode with $$[\mathrm{Zn$$^{2+}$$}] = 1.00 	imes 10$$^{-2}$$ M

Final Exam: Chem 112

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