Question 1

Why doesn't water produce $$[H^+] = 10$$^{-7}$$\ \mathrm{M}$$ and $$[OH^-] = 10$$^{-7}$$\ \mathrm{M}$$ when HBr is added to it?

Accepted Answer

Because the addition of HBr, a strong acid, increases $$[H^+]$$ far above $$10^{-7}$$\ \mathrm{M}$$, suppressing the autoionization of water.

Question 2

A 0.0450 M solution of benzoic acid has a pH of 2.78. Calculate the $$pK_a$$ for this acid.

Accepted Answer

$$pK_a = 4.20$$

Question 3

Why does squeezing lemon (acidic) onto fish reduce the fishy smell?

Accepted Answer

The acid reacts with amines to form non-volatile ammonium salts, reducing the odor.

Question 4

Which equation would you use 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 5

A buffer is prepared using 0.200 moles of a neutral acid and its conjugate base. If the desired pH is 1.65 and the $$pK_a of $$the acid is 1.95, how many moles of conjugate base are needed? (Use the Henderson-Hasselbalch equation.)

Accepted Answer

0.089 moles

Question 6

Why is the pH of a buffer nearly independent of its concentration?

Accepted Answer

Because the ratio of acid to base determines pH, not their absolute concentrations.

Question 7

Why does buffer capacity increase as the concentration of buffer increases?

Accepted Answer

Because higher concentrations provide more acid and base to neutralize added strong acids or bases.

Question 8

Given a 0.060 M solution of trimethylamine, $$(CH_3$)_3N$$, calculate the pH if $$K_b = 6.3 	imes 10$$^{-5}$$.

Accepted Answer

pH = 11.37

Question 9

A salt, $$BH^+$$ClO_4$$^-$$, is formed from a weak base $$B$$ ($$K_b = 1.00 	imes 10$$^{-4}$$) and perchloric acid. What is the pH of a 0.100 M solution of BH$$^+$$?

Accepted Answer

pH = 4.00

Question 10

When making a buffer by adding HCl or NaOH to the neutral form of a conjugate pair, why do you need to add fewer moles than when mixing the acid and base directly?

Accepted Answer

Because the added strong acid or base reacts completely, shifting the equilibrium and requiring less to achieve the same pH.

Question 11

Which of the following best explains why covalent compounds like amines have higher vapor pressures than ionic compounds?

Accepted Answer

Covalent compounds have weaker intermolecular forces, allowing them to evaporate more easily.

Question 12

If you have a buffer with $$[HA] = 0.10\ \mathrm{M}$$ and $$[A^-] = 0.10\ \mathrm{M}$$, and $$pK_a = 4.75$$, what is the pH?

Accepted Answer

$$pH = 4.75$$

Question 13

Which of the following is the correct expression for the base dissociation constant $$K_b$$ for trimethylamine, $$(CH_3$)_3N$$?

Accepted Answer

$$K_b = \frac{[(CH_3$)_3NH^+][OH^-]}{[(CH_3$)_3N]}$$

Analytical Chemistry Study Guidance: Acids, Bases, Equilibria, and Buffers

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