HL Paper 1

A buffer solution is formed by mixing equal volumes of 1.00 moldm31.00 moldm3 propanoic acid and 0.500 moldm3 potassium propanoate.

What is the concentration, in moldm3, of [H+(aq)] in this buffer solution? (Ka for propanoic acid is 1.30×105.)

A.     2.60×105

B.     1.95×105

C.     1.30×105

D.     0.650×105

Markscheme

A

Examiners report

This proved to be answered correctly by fewest candidates (37.59%) with many choosing option D, reversing [HA] and [A].




The pKa 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.     20.0 cm3 of 1.0 moldm3 CH3COOH and 10.0 cm3 of 1.0 moldm3 NaOH

B.     20.0 cm3 of 1.0 moldm3 CH3COOH and 20.0 cm3 of 1.0 moldm3 NaOH

C.     10.0 cm3 of 1.0 moldm3 CH3COOH and 20.0 cm3 of 1.0 moldm3 NaOH

D.     14.8 cm3 of 1.0 moldm3 CH3COOH and 10.0 cm3 of 1.0 moldm3 NaOH

Markscheme

A

Examiners report

[N/A]



Which mixture will form a buffer in aqueous solution?

A.     0.10 mol NH3+0.20 mol HCl

B.     0.10 mol NH3+0.20 mol NaOH

C.     0.10 mol NaOH+0.20 mol KCl

D.     0.20 mol NH3+0.10 mol HCl

Markscheme

D

Examiners report

[N/A]



Which mixtures act as buffer solutions?

I.     100 cm3 0.1 moldm3 ethanoic acid and 100 cm3 0.1 moldm3 sodium ethanoate

II.     100 cm3 0.1 moldm3 ethanoic acid and 50 cm3 0.1 moldm3 sodium hydroxide

III.     100 cm3 0.1 moldm3 ethanoic acid and 100 cm3 0.5 moldm3 sodium hydroxide

A.     I and II only

B.     I and III only

C.     II and III only

D.     I, II and III

Markscheme

A

Examiners report

[N/A]