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 would NOT result in a buffer solution?

Accepted Answer

A mixture of hydrochloric acid and sodium chloride.

Question 3

What is the main function of a buffer solution in the human body?

Accepted Answer

To maintain a constant pH despite the addition of acids or bases.

Question 4

Which equation correctly represents the Henderson-Hasselbalch equation for a weak acid (HA) and its conjugate base (A‒)?

Accepted Answer

$$pH = pK_a + \log \frac{[A^-]}{[HA]}$$

Question 5

A buffer is prepared by mixing 0.10 mol of acetic acid ($$HC_2H_3O_2) $$and 0.10 mol of sodium acetate ($$NaC_2H_3O_2) in $$enough water to make 1.0 L of solution. If $$K_a$$ for acetic acid is $$1.8 	imes 10$$^{-5}$$, what is the pH of the buffer?

Accepted Answer

$$pH = 4.74$$

Question 6

If a small amount of strong acid is added to a buffer solution containing $$HA$$ and $$A^-$$, what is the primary chemical change that occurs?

Accepted Answer

$$A^-$$ reacts with $$H_3O^+ to $$form $$HA$$ and $$H_2O$$

Question 7

Which of the following statements about buffer solutions is FALSE?

Accepted Answer

A buffer solution can be made by mixing a strong acid with its conjugate base.

Question 8

A buffer is made by mixing 0.15 M $$Na_2C_2O_4$$ and 0.05 M $$NaHC_2O_4 in 100 mL of $$water. Given $$pK_{a2} = 4.29$$ for $$HC_2O_4^-$$, what is the pH of the buffer?

Accepted Answer

$$pH = 4.77$$

Question 9

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

Accepted Answer

Because the ratio of base to acid remains constant upon dilution.

Question 10

A buffer solution is prepared using 0.20 M ammonia ($$NH_3) $$and 0.50 M ammonium chloride ($$NH_4Cl). $$Given $$K_b$$ for ammonia is $$1.8 	imes 10$$^{-5}$$, what is the pK_a$ of NH_4$^+$$?

Accepted Answer

$$pK_a = 9.25 ($$calculated as $$pK_a = 14 - pK_b)$$

Question 11

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

Accepted Answer

It cannot be used when the acid dissociation constant is greater than $$10^{-3}.$$

Question 12

A student prepares a buffer using 0.10 M $$HC_2H_3O_2$$ and 0.10 M $$NaC_2H_3O_2. If $$the student dilutes the buffer to twice its original volume, what happens to the pH?

Accepted Answer

The pH remains unchanged.

Question 13

Which of the following real-world scenarios is most directly related to the action of a buffer system?

Accepted Answer

The resistance of blood pH to changes after eating acidic foods.

Question 14

If the ratio $$\frac{[A^-]}{[HA]} in a $$buffer solution is 0.1, how does the pH compare to the $$pK_a$$?

Accepted Answer

The pH is 1 unit less than the $$pK_a.$$

Question 15

A buffer is prepared using 0.10 M $$H_2CO_3$$ and 0.10 M $$NaHCO_3. If$$ $$K_a$$ for $$H_2CO_3 is$$ $$4.3 	imes 10$$^{-7}$$, what is the pH of the buffer?

Accepted Answer

$$pH = 6.37$$

Question 16

Which of the following best describes buffer capacity?

Accepted Answer

The amount of acid or base a buffer can neutralize before a significant pH change occurs.

Question 17

In preparing a buffer solution in the laboratory, why is it often necessary to adjust the pH after mixing the calculated amounts of acid and conjugate base?

Accepted Answer

Because uncertainties in dissociation constants and simplifications in calculations can cause the actual pH to differ from the predicted value.

Question 18

Which of the following is TRUE regarding the preparation of a buffer from sodium bioxalate ($$NaHC_2O_4) $$and sodium oxalate ($$Na_2C_2O_4$$)?

Accepted Answer

The relevant $$pK_a is $$that of $$HC_2O_4^-$$, and the buffer pH is calculated using the ratio $$\frac{[C_2O_4$$^{2-}$$]}{[HC_2O_4^-]}.$$

Question 19

A buffer solution is most effective when:

Accepted Answer

The concentrations of acid and conjugate base are equal.

Aqueous Ionic Equilibria: Buffer Solutions and Their Properties

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