Question 1

Which of the following best describes the function of a buffer solution in a biological system?

Accepted Answer

It maintains a constant pH by neutralizing small amounts of added acid or base.

Question 2

A buffer solution is prepared by mixing 0.10 M acetic acid ($$CH_3COOH) $$and 0.10 M sodium acetate ($$CH_3COONa). If 0.01 $$mol of HCl is added to 1.0 L of this buffer, what will happen to the pH?

Accepted Answer

The pH will decrease only slightly due to the buffer's ability to neutralize added acid.

Question 3

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

Accepted Answer

$$pH = pK_a + \log_{10} \left( \frac{[A^-]}{[HA]} \right)$$

Question 4

A buffer is made by mixing 0.20 mol of $$NH_3$$ and 0.10 mol of $$NH_4Cl in 1.0 L of $$solution. The $$pK_b of $$ammonia is 4.75. What is the pH of the buffer?

Accepted Answer

$$pH = 9.25 + \log_{10} \left( \frac{0.20}{0.10} \right) = 9.25 + 0.30 = 9.55$$

Question 5

If 0.01 mol of NaOH is added to 1.0 L of a buffer solution containing 0.10 M $$CH_3COOH$$ and 0.10 M $$CH_3COONa$$, what is the new concentration of $$CH_3COOH$$ after the reaction?

Accepted Answer

$$[CH_3COOH] = 0.10 - 0.01 = 0.09 M$$

Question 6

Which of the following best explains why the pH of a buffer solution changes very little when a small amount of strong acid is added?

Accepted Answer

The weak base in the buffer reacts with the added acid to form its conjugate acid, minimizing pH change.

Question 7

A buffer solution contains 0.15 M formic acid ($$HCOOH$$, $$pK_a = 3.75) $$and 0.215 M sodium formate ($$HCOONa). $$What is the pH of the solution?

Accepted Answer

$$pH = 3.75 + \log_{10} \left( \frac{0.215}{0.15} \right) = 3.75 + 0.16 = 3.91$$

Question 8

Which statement about the Henderson-Hasselbalch equation is correct?

Accepted Answer

It is valid only when the ratio $$\frac{[A^-]}{[HA]} is $$between 0.1 and 10.

Question 9

A buffer solution is made by mixing 0.10 M $$CH_3COOH$$ and 0.10 M $$CH_3COONa. If 0.01 $$mol of HCl is added to 1.0 L of this buffer, what is the final concentration of $$CH_3COONa$$?

Accepted Answer

$$[CH_3COONa] = 0.10 + 0.01 = 0.11 M$$

Question 10

Which of the following reactions represents the buffer action when a strong acid is added to a solution containing ammonia and ammonium chloride?

Accepted Answer

$$NH_3 + H$$^+ \rightarrow $$NH_4$$^+$$

Question 11

A buffer solution is prepared with 0.10 M $$CH_3COOH$$ and 0.10 M $$CH_3COONa. $$What is the effect on pH if 0.01 mol of NaOH is added to 1.0 L of this buffer?

Accepted Answer

The pH will increase slightly because the buffer neutralizes the added base.

Question 12

Which of the following is true about the pH change in a buffered solution compared to an unbuffered solution when a strong acid is added?

Accepted Answer

The pH change in a buffered solution is much smaller than in an unbuffered solution.

Question 13

What is the main chemical principle that allows a buffer to resist changes in pH?

Accepted Answer

The presence of both a weak acid and its conjugate base, which react with added acids or bases.

Question 14

A buffer solution contains 0.10 M $$CH_3COOH$$ and 0.10 M $$CH_3COONa. If 0.01 $$mol of NaOH is added to 1.0 L of this buffer, what is the new ratio $$\frac{[A^-]}{[HA]}$$ after the reaction?

Accepted Answer

$$\frac{0.11}{0.09}$$

Question 15

Which of the following is a correct application of the Henderson-Hasselbalch equation for a buffer made from 0.10 M $$CH_3COOH$$ and 0.10 M $$CH_3COONa$$ with $$pK_a = 4.74$$?

Accepted Answer

$$pH = 4.74 + \log_{10} \left( \frac{0.10}{0.10} \right) = 4.74$$

Question 16

A buffer solution is made by mixing 0.10 M $$NH_3$$ and 0.10 M $$NH_4Cl. If 0.01 $$mol of HCl is added to 1.0 L of this buffer, what is the new concentration of $$NH_3$$?

Accepted Answer

$$[NH_3$] = 0.10 - 0.01 = 0.09 M$$

Question 17

Which of the following best describes the effect of adding a strong base to a buffer solution containing $$CH_3COOH$$ and $$CH_3COONa$$?

Accepted Answer

The weak acid reacts with the base to form its conjugate base, minimizing the pH increase.

Acid-Base Buffers and the Henderson-Hasselbalch Equation

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