A buffer solution is formed by mixing equal volumes of ${\text{1.00 mol}}\,{\text{d}}{{\text{m}}^{ - 3}}$ propanoic acid and ${\text{0.500 mol}}\,{\text{d}}{{\text{m}}^{ - 3}}$ potassium propanoate.

What is the concentration, in ${\text{mol}}\,{\text{d}}{{\text{m}}^{ - 3}}$, of ${\text{[}}{{\text{H}}^ + }{\text{(aq)]}}$ in this buffer solution? (${K_{\text{a}}}$ for propanoic acid is $1.30 \times {10^{ - 5}}$.)

A.     $2.60 \times {10^{ - 5}}$

B.     $1.95 \times {10^{ - 5}}$

C.     $1.30 \times {10^{ - 5}}$

D.     $0.650 \times {10^{ - 5}}$

A

This proved to be answered correctly by fewest candidates (37.59%) with many choosing option D, reversing [HA] and ${\text{[}}{{\text{A}}^ - }{\text{]}}$.

The ${\text{p}}{K_{\text{a}}}$ of ethanoic acid is 4.8 at 298 K. Which combination will produce a buffer solution with a pH of 4.8 at 298 K?

A.     ${\text{20.0 c}}{{\text{m}}^{\text{3}}}{\text{ of 1.0 mol}}\,{\text{d}}{{\text{m}}^{ - {\text{3}}}}{\text{ C}}{{\text{H}}_{\text{3}}}{\text{COOH and 10.0 c}}{{\text{m}}^{\text{3}}}{\text{ of 1.0 mol}}\,{\text{d}}{{\text{m}}^{ - {\text{3}}}}{\text{ NaOH}}$

B.     ${\text{20.0 c}}{{\text{m}}^{\text{3}}}{\text{ of 1.0 mol}}\,{\text{d}}{{\text{m}}^{ - {\text{3}}}}{\text{ C}}{{\text{H}}_{\text{3}}}{\text{COOH and 20.0 c}}{{\text{m}}^{\text{3}}}{\text{ of 1.0 mol}}\,{\text{d}}{{\text{m}}^{ - {\text{3}}}}{\text{ NaOH}}$

C.     ${\text{10.0 c}}{{\text{m}}^{\text{3}}}{\text{ of 1.0 mol}}\,{\text{d}}{{\text{m}}^{ - {\text{3}}}}{\text{ C}}{{\text{H}}_{\text{3}}}{\text{COOH and 20.0 c}}{{\text{m}}^{\text{3}}}{\text{ of 1.0 mol}}\,{\text{d}}{{\text{m}}^{ - {\text{3}}}}{\text{ NaOH}}$

D.     ${\text{14.8 c}}{{\text{m}}^{\text{3}}}{\text{ of 1.0 mol}}\,{\text{d}}{{\text{m}}^{ - {\text{3}}}}{\text{ C}}{{\text{H}}_{\text{3}}}{\text{COOH and 10.0 c}}{{\text{m}}^{\text{3}}}{\text{ of 1.0 mol}}\,{\text{d}}{{\text{m}}^{ - {\text{3}}}}{\text{ NaOH}}$

A

Which mixture will form a buffer in aqueous solution?

A.     ${\text{0.10 mol N}}{{\text{H}}_{\text{3}}} + {\text{0.20 mol HCl}}$

B.     ${\text{0.10 mol N}}{{\text{H}}_{\text{3}}} + {\text{0.20 mol NaOH}}$

C.     ${\text{0.10 mol NaOH}} + {\text{0.20 mol KCl}}$

D.     ${\text{0.20 mol N}}{{\text{H}}_{\text{3}}} + {\text{0.10 mol HCl}}$

D

Which mixtures act as buffer solutions?

I.     ${\text{100 c}}{{\text{m}}^{\text{3}}}{\text{ 0.1 mol}}\,{\text{d}}{{\text{m}}^{ - 3}}$ ethanoic acid and ${\text{100 c}}{{\text{m}}^{\text{3}}}{\text{ 0.1 mol}}\,{\text{d}}{{\text{m}}^{ - 3}}$ sodium ethanoate

II.     ${\text{100 c}}{{\text{m}}^{\text{3}}}{\text{ 0.1 mol}}\,{\text{d}}{{\text{m}}^{ - 3}}$ ethanoic acid and ${\text{50 c}}{{\text{m}}^{\text{3}}}{\text{ 0.1 mol}}\,{\text{d}}{{\text{m}}^{ - 3}}$ sodium hydroxide

III.     ${\text{100 c}}{{\text{m}}^{\text{3}}}{\text{ 0.1 mol}}\,{\text{d}}{{\text{m}}^{ - 3}}$ ethanoic acid and ${\text{100 c}}{{\text{m}}^{\text{3}}}{\text{ 0.5 mol}}\,{\text{d}}{{\text{m}}^{ - 3}}$ sodium hydroxide

A.     I and II only

B.     I and III only

C.     II and III only

D.     I, II and III

A