Q: Which of the following weak acid–conjugate base combinations would result in an ideal buffer solution with a pH of 9.4?

hydrocyanic acid (HCN) and lithium cyanide (Ka = 4.9 \times $$10^{-10})$$

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

$$pH = pK_a + \log \left( \frac{[\text{CB}]}{[\text{WA}]} \right)$$

Question 1

Which of the following best describes the buffer region on a weak acid–strong base titration curve?

Accepted Answer

The region before the equivalence point where the pH increases gradually and both weak acid and its conjugate base are present.

Question 2

A buffer solution is most effective when:

Accepted Answer

The concentrations of weak acid and conjugate base are equal.

Question 3

Given the titration curve below, which indicator would be most appropriate if the equivalence point occurs at pH = 4.5?

Accepted Answer

Methyl Red (pH range 4.2–6.2)

Question 4

Which of the following combinations would result in a buffer solution?

Accepted Answer

0.35 M CH3CO2H and 0.34 M CH3CO2–

Question 5

Calculate the pH of a buffer solution containing 2.0 M nitrous acid (HNO2) and 1.48 M lithium nitrite (LiNO2). $$K_a = 4.6 	imes 10$$^{-4}$$.

Accepted Answer

$$pH = 3.70$$

Question 6

Which of the following actions will destroy a buffer composed of 0.50 L of 1.44 M H3PO4 and 0.60 L of 1.25 M NaH2PO4?

Accepted Answer

Addition of 0.85 moles of HCl

Question 7

For the titration of 100.0 mL of 0.40 M HCl with 0.40 M NaOH, which volume of NaOH would place it in excess?

Accepted Answer

110.0 mL

Question 8

Which of the following weak acid–conjugate base combinations would result in an ideal buffer solution with a pH of 9.4?

Accepted Answer

hydrocyanic acid (HCN) and lithium cyanide (Ka = 4.9 	imes $$10^{-10})$$

Question 9

A solution contains 100.0 mL of 0.550 M sodium nitrite, NaNO2. What is the pH after the addition of 180.0 mL of 0.400 M HClO4? (Ka of HNO2 is $$4.6 	imes 10$$^{-4}$$)

Accepted Answer

$$pH = 1.00$$

Question 10

Which of the following compounds will become more soluble in basic solution?

Accepted Answer

Al(OH)3 (s)

Question 11

If $$K_{sp} of $$AgCl is $$1.77 	imes 10$$^{-10}$$ and K_f$ of Ag(NH3)2+ is 1.7$$ 	imes $$10^7$$, what is the solubility of AgCl in 2.0 M NH3?

Accepted Answer

$$1.74 	imes 10$$^{-2}$$ M

Question 12

Which statement is true regarding the relationship between $$K_{sp}$$ and $$Q$$ for precipitation?

Accepted Answer

If $$Q \u003e K_{sp}$$, the solution is supersaturated and precipitation occurs.

Question 13

Which of the following titration curves best represents the titration of a weak base with a strong acid?

Accepted Answer

A curve starting at high pH, decreasing gradually, with an equivalence point below pH 7.

Question 14

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

Accepted Answer

$$pH = pK_a + \log \left( \frac{[	ext{CB}]}{[	ext{WA}]} ight)$$

Question 15

A student is titrating a weak acid with a strong base. At the half-equivalence point, which of the following is true?

Accepted Answer

The pH equals the pKa of the weak acid.

Question 16

Which of the following best explains why the addition of NaF to a solution of HF decreases the solubility of HF?

Accepted Answer

The common ion effect shifts the equilibrium to the left, decreasing solubility.

Question 17

Which of the following indicators would be best for a titration with an equivalence point at pH = 9.0?

Accepted Answer

Phenolphthalein (pH range 8.3–10.0)

Aqueous Ionic Equilibrium: Buffers, Titrations, and Solubility

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