Q: What is the correct form of the Henderson-Hasselbalch equation for calculating the pH of a buffer?

$$\text{pH} = \text{p}K_a + \log \left( \frac{[\text{A}^-]}{[\text{HA}]} \right)$$

Q: A 1.0 L buffer solution contains 0.10 mol HA and 0.10 mol A-. If 0.010 mol NaOH is added, what is the new pH if pKa = 5.00?

$$\text{pH} = 5.00 + \log \left( \frac{0.11}{0.09} \right) = 5.09$$

Q: A buffer solution is prepared with 0.25 M formic acid ($$\text{HCO}_2\text{H}$$, $$K_a = 1.8 \times 10$$^{-4}$$) and 0.50 M sodium formate ($$\text{NaHCO}_2$$). What is the pH?

$$\text{pH} = 3.74 + \log \left( \frac{0.50}{0.25} \right) = 4.04$$

Q: Which equation is used to calculate the pH of a buffer after addition of a strong acid or base?

$$\text{pH} = \text{p}K_a + \log \left( \frac{[\text{A}^-]}{[\text{HA}]} \right)$$

Q: A 500.0 mL buffer solution contains 0.25 M formic acid and 0.50 M sodium formate. After adding 1.0 mL of 2.0 M HCl, what is the new pH? ($$K_a = 1.8 \times 10$$^{-4}$$)

$$\text{pH} = 3.74 + \log \left( \frac{0.248}{0.127} \right) = 4.03$$

Question 1

Which of the following best describes a buffer solution?

Accepted Answer

A solution that resists changes in pH when small amounts of acid or base are added.

Question 2

What is the correct form of the Henderson-Hasselbalch equation for calculating the pH of a buffer?

Accepted Answer

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

Question 3

A buffer is most effective when:

Accepted Answer

The concentrations of acid and conjugate base are equal.

Question 4

What is the effective pH range for a buffer with a pKa of 5.00?

Accepted Answer

pH 4.00 to 6.00

Question 5

A 1.0 L buffer solution contains 0.10 mol HA and 0.10 mol A-. If 0.010 mol NaOH is added, what is the new pH if pKa = 5.00?

Accepted Answer

$$	ext{pH} = 5.00 + \log \left( \frac{0.11}{0.09} ight) = 5.09$$

Question 6

Which factor does NOT increase the effectiveness of a buffer?

Accepted Answer

A very low concentration of both acid and base.

Question 7

A buffer solution is prepared with 0.25 M formic acid ($$	ext{HCO}_2	ext{H}$$, $$K_a = 1.8 	imes 10$$^{-4}$$) and 0.50 M sodium formate ($$	ext{NaHCO}_2$$). What is the pH?

Accepted Answer

$$	ext{pH} = 3.74 + \log \left( \frac{0.50}{0.25} ight) = 4.04$$

Question 8

A chemist needs to prepare a carbonate buffer of pH 10.00 using 1.5 L of 0.20 M NaHCO$$_3$$ and Na$$_2CO$_3$$ ($$K_a$$ for HCO$$_3^-$$ = $$4.7 	imes 10$$^{-11}$$). How many grams of Na_2$CO_3$ are required? (M.W. = 105.99 g/mol)

Accepted Answer

15 g

Question 9

What happens to the pH of a buffer solution when a small amount of strong acid is added?

Accepted Answer

The pH decreases slightly.

Question 10

Which equation is used to calculate the pH of a buffer after addition of a strong acid or base?

Accepted Answer

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

Question 11

A buffer solution is most resistant to pH changes when:

Accepted Answer

The concentrations of acid and base are both high and equal.

Question 12

What is the lowest pH for an effective buffer with pKa = 7.00?

Accepted Answer

pH = 6.00

Question 13

A 500.0 mL buffer solution contains 0.25 M formic acid and 0.50 M sodium formate. After adding 1.0 mL of 2.0 M HCl, what is the new pH? ($$K_a = 1.8 	imes 10$$^{-4}$$)

Accepted Answer

$$	ext{pH} = 3.74 + \log \left( \frac{0.248}{0.127} ight) = 4.03$$

Question 14

Which of the following is NOT a composition of a buffer?

Accepted Answer

A strong acid and a strong base.

Question 15

If the ratio $$\frac{[	ext{base}]}{[	ext{acid}]} in a $$buffer is 0.01, what can be said about the buffer's effectiveness?

Accepted Answer

The buffer is outside its effective range and not very effective.

Question 16

What is the main purpose of using an ICE table in buffer calculations?

Accepted Answer

To track the changes in concentrations of acid and base during reactions.

Question 17

When preparing a buffer, why is it important to use the small x approximation?

Accepted Answer

It simplifies calculations when x is much smaller than the initial concentrations.

Question 18

Which of the following statements about buffer capacity is correct?

Accepted Answer

Buffer capacity is highest when the concentrations of acid and base are high and equal.

Buffer Solutions: Calculation, Effectiveness, and Applications

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