
HL Paper 1
A buffer solution is formed by mixing equal volumes of 1.00 moldm−31.00 moldm−3 propanoic acid and 0.500 moldm−3 potassium propanoate.
What is the concentration, in moldm−3, of [H+(aq)] in this buffer solution? (Ka for propanoic acid is 1.30×10−5.)
A. 2.60×10−5
B. 1.95×10−5
C. 1.30×10−5
D. 0.650×10−5
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 moldm−3 CH3COOH and 10.0 cm3 of 1.0 moldm−3 NaOH
B. 20.0 cm3 of 1.0 moldm−3 CH3COOH and 20.0 cm3 of 1.0 moldm−3 NaOH
C. 10.0 cm3 of 1.0 moldm−3 CH3COOH and 20.0 cm3 of 1.0 moldm−3 NaOH
D. 14.8 cm3 of 1.0 moldm−3 CH3COOH and 10.0 cm3 of 1.0 moldm−3 NaOH
Markscheme
A
Examiners report
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
Which mixtures act as buffer solutions?
I. 100 cm3 0.1 moldm−3 ethanoic acid and 100 cm3 0.1 moldm−3 sodium ethanoate
II. 100 cm3 0.1 moldm−3 ethanoic acid and 50 cm3 0.1 moldm−3 sodium hydroxide
III. 100 cm3 0.1 moldm−3 ethanoic acid and 100 cm3 0.5 moldm−3 sodium hydroxide
A. I and II only
B. I and III only
C. II and III only
D. I, II and III
Markscheme
A