Question 1

Which of the following combinations can be used to prepare an effective acidic buffer solution?

Accepted Answer

Weak acid and its conjugate base

Question 2

A buffer solution is prepared by mixing 0.1 M acetic acid ($CH_3COOH$) and 0.1 M sodium acetate ($CH_3COONa$). If the $pK_a$ of acetic acid is 4.76, what is the pH of the buffer?

Accepted Answer

$pH = 4.76$

Question 3

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

Accepted Answer

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

Question 4

A buffer solution is made by mixing 0.05 M $NH_3$ and 0.02 M $NH_4Cl$. If $K_b$ for $NH_3$ is $1.8 	imes 10^{-5}$, what is the pH of the solution?

Accepted Answer

$pOH = pK_b + \log \frac{[NH_4^+]}{[NH_3]} = 4.74$, so $pH = 14 - 4.74 = 9.26$

Question 5

Which of the following statements about buffer capacity is correct?

Accepted Answer

Buffer capacity increases as the concentrations of both the weak acid and its conjugate base increase.

Question 6

A buffer solution is most effective when:

Accepted Answer

The concentrations of the weak acid and its conjugate base are equal.

Question 7

Which of the following is NOT a suitable buffer system for maintaining a pH near 9.0?

Accepted Answer

Acetic acid/acetate

Question 8

If 100 mL of 0.01 M HCl is added to 200 mL of an acetic acid/acetate buffer, what will happen to the pH?

Accepted Answer

The pH will decrease slightly, but remain close to the original value due to the buffer action.

Question 9

Which of the following is the correct Henderson-Hasselbalch equation for a buffer made from a weak base and its conjugate acid?

Accepted Answer

$pOH = pK_b + \log \frac{[BH^+]}{[B]}$

Question 10

A buffer solution is prepared using 0.2 M $NH_3$ and 0.3 M $NH_4Cl$ in 400 mL. How many mL of 0.05 M NaOH must be added to increase the pH by 0.4 units?

Accepted Answer

Approximately 80 mL

Question 11

Which of the following buffer systems would be most suitable for maintaining a pH of 7.3 in a biochemical experiment?

Accepted Answer

Phosphate buffer ($H_2PO_4^-/HPO_4^{2-}$)

Question 12

A buffer solution is prepared by dissolving 1.00 g of potassium hydrogen phthalate (KHP, $C_8H_5O_4K$, FM = 204.22) and 1.20 g of disodium phthalate ($C_8H_4O_4Na_2$, FM = 210.09) in 50.0 mL water. If the $pK_a$ of KHP is 5.408, what is the pH of the solution?

Accepted Answer

$pH = 5.408 + \log \frac{1.20/210.09}{1.00/204.22}$

Question 13

Which of the following is a correct statement about the effective pH range of a buffer?

Accepted Answer

A buffer is most effective within $pK_a \pm 1$ of the weak acid.

Question 14

You are asked to prepare 100 mL of a 0.1 M phthalate buffer at pH 5.50. Which starting materials would be most appropriate?

Accepted Answer

Phthalic acid and sodium phthalate

Question 15

Which of the following is NOT a property of buffer solutions?

Accepted Answer

They are made from a strong acid and its salt.

Question 16

A buffer solution contains 0.03 M $NH_3$ and 0.02 M $NH_4Cl$. If 5 mL of 0.10 M NaOH is added to 100 mL of this buffer, what will happen to the pH?

Accepted Answer

The pH will increase slightly, but the buffer will resist drastic change.

Question 17

Which of the following is the correct formula for buffer capacity ($\beta$)?

Accepted Answer

$\beta = \frac{	ext{number of moles of strong acid or base added}}{\Delta pH 	imes 	ext{volume of buffer (L)}}$

Buffer Solutions (Tampon Çözeltiler) in Analytical Chemistry

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