Q: A 0.085 M aqueous solution of a monoprotic acid (HA) has a pH of 3.30. What is the concentration of $$\mathrm{H_3O^+} in $$the solution?

$$5.02 \times 10$$^{-4}$$\ \mathrm{M}$$

Q: A $$0.155\ \mathrm{M}$$ solution of $$\mathrm{H_2CO_3}$$ has $$K_{a,1} = 4.3 \times 10$$^{-7}$$ and K$$_{a,2} = 5.6 \times $$10^{-11}. $$What is the concentration of $$\mathrm{$$HCO_3$$^-} at $$equilibrium after the first dissociation?

$$2.58 \times 10$$^{-4}$$\ \mathrm{M}$$

Q: A solution contains $$0.022\ \mathrm{M} Fe$^{2+}$$ and $$0.014\ \mathrm{M} Mg$^{2+}$$. $$K_{sp}$$ for FeCO$$_3 is$$ $$3.0 \times 10$$^{-11}$$ and for MgCO_3$ is 6.82$$ \times $$10^{-6}. $$What is the minimum concentration of CO$$_3$$^{2-}$$ needed to begin precipitation of FeCO_3$?

$$1.4 \times 10$$^{-9}$$\ \mathrm{M}$$

Q: What is the maximum concentration of CO$$_3$$^{2-}$$ that can be added before MgCO_3$ begins to precipitate in the above solution?

$$4.9 \times 10$$^{-4}$$\ \mathrm{M}$$

Q: After FeCO$$_3$$ begins to precipitate, what is the remaining concentration of Fe$$^{2+}$$ when MgCO$$_3$$ just starts to precipitate?

$$6.3 \times 10$$^{-8}$$\ \mathrm{M}$$

Q: Which equation is used to calculate the pH of a buffer solution containing a weak acid and its conjugate base?

$$\mathrm{pH = pK_a + \log \left( \frac{[\text{base}]}{[\text{acid}]} \right)}$$

Question 1

A 0.085 M aqueous solution of a monoprotic acid (HA) has a pH of 3.30. What is the concentration of $$\mathrm{H_3O^+} in $$the solution?

Accepted Answer

$$5.02 	imes 10$$^{-4}$$\ \mathrm{M}$$

Question 2

Given the reaction $$\mathrm{HA\ (aq) + H_2O\ (l) ightarrow A^-\ (aq) + H_3O^+\ (aq)}$$, and the initial concentration of HA is $$0.085\ \mathrm{M}$$, with $$[H_3O^+] = 5.02 	imes 10$$^{-4}$$\ \mathrm{M} at $$equilibrium, what is the value of the acid dissociation constant $$K_a$$?

Accepted Answer

$$3.0 	imes 10$$^{-6}$$

Question 3

A solution contains $$0.150\ \mathrm{M} HF. $$Given $$K_a = 3.5 	imes 10$$^{-4}$$, what is the pH of the solution?

Accepted Answer

$$2.14$$

Question 4

Why can the contribution of $$\mathrm{HCOOH} to$$ $$[H_3O^+] be $$neglected in a mixture of $$0.100\ \mathrm{M} HF $$and $$0.100\ \mathrm{M}$$ HCOOH?

Accepted Answer

Because $$K_a$$ for HCOOH is much smaller than that for HF, so its ionization is negligible compared to HF.

Question 5

A $$0.155\ \mathrm{M}$$ solution of $$\mathrm{H_2CO_3}$$ has $$K_{a,1} = 4.3 	imes 10$$^{-7}$$ and K$$_{a,2} = 5.6 	imes $$10^{-11}. $$What is the concentration of $$\mathrm{$$HCO_3$$^-} at $$equilibrium after the first dissociation?

Accepted Answer

$$2.58 	imes 10$$^{-4}$$\ \mathrm{M}$$

Question 6

For the reaction $$\mathrm{C_5H_5N\ (aq) + H_2O\ (l) ightarrow C_5H_5NH^+\ (aq) + OH^-\ (aq)}$$ with $$K_b = 1.7 	imes 10$$^{-9}$$ and $$[C_5H_5N] = 0.125\ \mathrm{M}$$, what is the pH of the solution?

Accepted Answer

$$9.16$$

Question 7

A buffer solution is $$0.125\ \mathrm{M} in $$HNO$$_2$$ ($$K_a = 4.6 	imes 10$$^{-4}$$) and 0.145$$\ \mathrm{M}$$ in NaNO_2$. What is the pH of the buffer?

Accepted Answer

$$3.40$$

Question 8

If $$1.5\ \mathrm{g} of $$HCl is added to the buffer solution described above, what is the new pH?

Accepted Answer

$$3.13$$

Question 9

A solution contains $$0.022\ \mathrm{M} Fe$^{2+}$$ and $$0.014\ \mathrm{M} Mg$^{2+}$$. $$K_{sp}$$ for FeCO$$_3 is$$ $$3.0 	imes 10$$^{-11}$$ and for MgCO_3$ is 6.82$$ 	imes $$10^{-6}. $$What is the minimum concentration of CO$$_3$$^{2-}$$ needed to begin precipitation of FeCO_3$?

Accepted Answer

$$1.4 	imes 10$$^{-9}$$\ \mathrm{M}$$

Question 10

What is the maximum concentration of CO$$_3$$^{2-}$$ that can be added before MgCO_3$ begins to precipitate in the above solution?

Accepted Answer

$$4.9 	imes 10$$^{-4}$$\ \mathrm{M}$$

Question 11

After FeCO$$_3$$ begins to precipitate, what is the remaining concentration of Fe$$^{2+}$$ when MgCO$$_3$$ just starts to precipitate?

Accepted Answer

$$6.3 	imes 10$$^{-8}$$\ \mathrm{M}$$

Question 12

A solution contains $$0.20\ \mathrm{M} Zn$^{2+}$$ and excess Ba(OH)$$_2$$. $$K_{sp}$$ for Zn(OH)$$_2 is$$ $$3.0 	imes 10$$^{-15}$$ and K_f$ for Zn(OH)$$_$$4^{2-} is$$ $$2.0 	imes 10$$^{5}$$. What is the pH of the solution after Zn(OH)_2$ dissolves as Zn(OH)$$_$$4^{2-}$$?

Accepted Answer

$$12.97$$

Question 13

Which of the following best describes the effect of adding a strong acid to a buffer solution?

Accepted Answer

The pH decreases slightly, but the buffer resists large changes in pH.

Question 14

In a titration of $$0.125\ \mathrm{M}$$ pyridine ($$C_5H_5N) $$with $$0.100\ \mathrm{M}$$ HCl, what is the volume of HCl required to reach the equivalence point if the initial volume of pyridine is $$25.0\ \mathrm{mL}$$?

Accepted Answer

$$31.25\ \mathrm{mL}$$

Question 15

Which equation is used to calculate the pH of a buffer solution containing a weak acid and its conjugate base?

Accepted Answer

$$\mathrm{pH = pK_a + \log \left( \frac{[	ext{base}]}{[	ext{acid}]} ight)}$$

Question 16

If $$K_{sp}$$ for FeCO$$_3 is$$ $$3.0 	imes 10$$^{-11}$$, what is the equilibrium expression for the solubility product?

Accepted Answer

$$K_{sp} = [Fe$$^{2+}$$][CO_3$^{2-}]$$

Question 17

A buffer is prepared by mixing $$0.125\ \mathrm{M}$$ HNO$$_2$$ and $$0.145\ \mathrm{M}$$ NaNO$$_2. If$$ $$1.5\ \mathrm{g}$$ NaOH is added, what happens to the ratio $$\frac{[	ext{base}]}{[	ext{acid}]}$$?

Accepted Answer

The ratio increases because NaOH converts acid to base.

Question 18

Which of the following statements about the solubility of Zn(OH)$$_2 in $$the presence of excess OH$$^- is $$correct?

Accepted Answer

The solubility increases due to formation of the complex ion Zn(OH)$$_4$$^{2-}$$.

General Chemistry II: Acid-Base Equilibria, Buffers, and Solubility Study Guide

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