Q: Which equation is most appropriate for calculating the pH of a buffer solution containing a weak acid and its conjugate base?

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

Q: Calculate the solubility of $$\mathrm{$$LaF_3$$} in $$pure water if $$K_{sp} = 2.0 \times 10$$^{-19}$$.

$$1.7 \times 10$$^{-5}$$~\mathrm{M}$$

Q: If $$K_a$$ for HF is $$7.2 \times 10$$^{-4}$$, what is the K_b$ for $$\mathrm{F^-}$$? (K_w = 1.0$$ \times $$10^{-14})$$

$$K_b = 1.4 \times 10$$^{-11}$$

Question 1

A student mixes 95 mL of 0.250 M formic acid ($$\mathrm{HCOOH}) $$with 55 mL of 0.250 M sodium formate ($$\mathrm{NaHCOO}). $$What is the resulting pH? ($$pK_a of $$formic acid = 3.75)

Accepted Answer

$$\mathrm{pH} = 3.87$$

Question 2

Which equation is most appropriate for calculating 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 3

A buffer is prepared by mixing 0.100 mol of acetic acid ($$\mathrm{CH_3COOH}) $$and 0.100 mol of sodium acetate ($$\mathrm{CH_3COONa}) in 1.0 L of $$solution. What is the pH if $$pK_a = 4.76$$?

Accepted Answer

$$\mathrm{pH} = 4.76$$

Question 4

Which of the following is a common mistake when using the Henderson-Hasselbalch equation?

Accepted Answer

Using the acid over base instead of base over acid

Question 5

Calculate the solubility of $$\mathrm{$$LaF_3$$} in $$pure water if $$K_{sp} = 2.0 	imes 10$$^{-19}$$.

Accepted Answer

$$1.7 	imes 10$$^{-5}$$~\mathrm{M}$$

Question 6

Which of the following best describes the effect of adding NaF to a saturated solution of $$\mathrm{$$LaF_3$$}$$?

Accepted Answer

The solubility of $$\mathrm{$$LaF_3$$}$$ decreases

Question 7

A titration is performed by adding 0.0500 M NaOH to 25.0 mL of 0.100 M HF. What is the pH after adding 12.5 mL of NaOH? ($$pK_a of HF = 3.17)$$

Accepted Answer

$$\mathrm{pH} = 3.77$$

Question 8

Which of the following is the correct expression for the solubility product constant ($$K_{sp}) $$for $$\mathrm{$$LaF_3$$}$$?

Accepted Answer

$$K_{sp} = [\mathrm{La$$^{3+}$$}][\mathrm{F^-}]^3$$

Question 9

If $$K_a$$ for HF is $$7.2 	imes 10$$^{-4}$$, what is the K_b$ for $$\mathrm{F^-}$$? (K_w = 1.0$$ 	imes $$10^{-14})$$

Accepted Answer

$$K_b = 1.4 	imes 10$$^{-11}$$

Question 10

A solution is made by mixing 0.250 mol of formic acid and 0.250 mol of sodium formate in 1.0 L of water. What is the ratio $$\frac{[\mathrm{HCOO^-}]}{[\mathrm{HCOOH}]}$$ when the pH is equal to the $$pK_a$$?

Accepted Answer

1

Question 11

Which of the following best explains why the pH at the equivalence point of a weak acid-strong base titration is greater than 7?

Accepted Answer

The conjugate base hydrolyzes to produce $$\mathrm{OH^-}$$

Question 12

What is the pH of a solution where $$[\mathrm{OH^-}] = 7.00 	imes 10$$^{-12}$$~\mathrm{M}$$?

Accepted Answer

$$\mathrm{pH} = 2.85$$

Question 13

Which shortcut can be used to calculate the pH of a buffer if the volumes of acid and base solutions are equal?

Accepted Answer

$$\mathrm{pH} = pK_a$$

Question 14

A solution contains $$0.010~\mathrm{M}$$ $$\mathrm{$$LaF_3$$}$$ and $$0.010~\mathrm{M}$$ $$\mathrm{NaF}. $$What is the effect on the solubility of $$\mathrm{$$LaF_3$$}$$ compared to pure water?

Accepted Answer

Solubility decreases due to common ion effect

Question 15

Which of the following is the correct relationship between $$K_a$$, $$K_b$$, and $$K_w$$?

Accepted Answer

$$K_a 	imes K_b = K_w$$

Question 16

A buffer solution is made by mixing 0.20 mol of a weak acid ($$HA) $$and 0.10 mol of its conjugate base ($$A^-) in 1.0 L of $$water. If $$pK_a = 4.50$$, what is the pH?

Accepted Answer

$$\mathrm{pH} = 4.20$$

Acid-Base Equilibria, Titrations, and Solubility: Study Notes

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