Question 1

Which of the following best describes a buffer solution?

Accepted Answer

A solution containing a weak acid and its conjugate base at a predetermined ratio.

Question 2

Which of the following combinations will NOT result in a buffer solution?

Accepted Answer

A mixture of hydrochloric acid and sodium chloride.

Question 3

What is the main reason why buffer solutions resist changes in pH upon addition of small amounts of strong acid or base?

Accepted Answer

The buffer components react with added H$$_3O$^+ or OH$^-$$, minimizing changes in their ratio.

Question 4

Given the buffer system HA/A$$^-$$, which equation correctly represents the relationship between pH, pK$$_a$$, and the concentrations of the buffer components?

Accepted Answer

$$\mathrm{pH} = \mathrm{p}K_a + \log \frac{[A^-]}{[HA]}$$

Question 5

A buffer is prepared by mixing 0.30 M acetic acid (HC$$_2H$_3O$_2) $$and 0.20 M sodium acetate (NaC$$_2H$_3O$_2). $$Given $$K_a = 1.8 	imes 10$$^{-5}$$, what is the pH of the buffer?

Accepted Answer

4.57

Question 6

Which of the following statements about buffer capacity is correct?

Accepted Answer

Buffer capacity increases as the total concentration of buffer components increases.

Question 7

A buffer solution is made by mixing 0.20 M ammonia (NH$$_3) $$and 0.50 M ammonium chloride (NH$$_4Cl). $$Given $$K_b$$ for NH$$_3 is$$ $$1.8 	imes 10$$^{-5}$$, what is the pH of the buffer? (K_w = 1.0$$ 	imes $$10^{-14})$$

Accepted Answer

8.85

Question 8

Which of the following best explains why dilution does not affect the pH of a buffer solution?

Accepted Answer

Because the ratio of the concentrations of the buffer components remains unchanged.

Question 9

Which of the following is a naturally occurring buffer system in human blood?

Accepted Answer

H$$_2CO$_3/$$HCO$$_3^-$$

Question 10

A buffer is prepared using sodium bioxalate (NaHC$$_2O$_4) $$and sodium oxalate (Na$$_2C$_2O$_4). If $$the desired pH is 4.77 and $$pK_{a2} is 4.29$$, what is the required ratio of [C$$_2O$_4$$^{2-}$$] to [HC_2$O_4$$^-$$]?

Accepted Answer

3.02

Question 11

Which of the following is a limitation of the Henderson-Hasselbalch equation?

Accepted Answer

It is inaccurate when the acid dissociation constant is greater than $$10^{-3}.$$

Question 12

Which of the following best describes the effect of adding a small amount of strong base to a HA/A$$^-$$ buffer solution?

Accepted Answer

The concentration of HA decreases and the concentration of A$$^-$$ increases.

Question 13

Which of the following equations is used to calculate the pH of a buffer made from a weak base (B) and its conjugate acid (HB$$^+$$)?

Accepted Answer

$$\mathrm{pH} = \mathrm{p}K_a + \log \frac{[B]}{[HB^+]}$$

Question 14

A student prepares a buffer solution using 0.050 M NaHC$$_2O$_4$$ and 0.15 M Na$$_2C$_2O$_4 in 100.0 mL of $$water. What mass of Na$$_2C$_2O$_4 ($$molar mass = 134.04 g/mol) is required?

Accepted Answer

2.01 g

Question 15

Which of the following best explains why the measured pH of a buffer solution may differ from the calculated value?

Accepted Answer

Uncertainties in dissociation constants and simplifications in calculations.

Question 16

Which of the following is true for a diprotic acid buffer system?

Accepted Answer

There are two buffer regions, each corresponding to a different acid dissociation.

Question 17

If a buffer solution is prepared with [A$$^-$$] = [HA], what is the relationship between pH and pK$$_a$$?

Accepted Answer

pH = pK$$_a$$

Question 18

A natural water source is less susceptible to acid rain if it contains a high concentration of which buffer component?

Accepted Answer

Bicarbonate ion (HCO$$_3^-)$$

Question 19

Which of the following steps is NOT part of the standard laboratory protocol for preparing a buffer solution?

Accepted Answer

Adding a large excess of strong acid to ensure complete reaction.

Aqueous Ionic Equilibria: Buffer Solutions and Their Properties

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