DP Chemistry (last assessment 2024)

Test builder »

Question 18N.3.sl.TZ0.14a

Select a Test
Date November 2018 Marks available [Maximum mark: 2] Reference code 18N.3.sl.TZ0.14a
Level sl Paper 3 Time zone TZ0
Command term Determine Question number a Adapted from N/A
a.
[Maximum mark: 2]
18N.3.sl.TZ0.14a

Buffer systems control pH in the body.

(a)

Determine the pH of a buffer solution that is 0.0100 mol dm−3 sodium hydrogen carbonate and 0.0200 mol dm−3 sodium carbonate, using section 1 of the data booklet.

Ka (hydrogen carbonate ion) = 4.8 × 10−11

[2]

Markscheme

ALTERNATIVE 1:

Using: pH = pKa + log  ( [ A − ] [ H A ] )

pKa = 10.32 ✔

pH = «10.32 + log  ( 0.0200 0.0100 ) =» 10.62 ✔

 

ALTERNATIVE 2:

[H+] «= Ka × ( 0.0100 0.0200 ) » = 2.4 × 10−11 ✔

pH = 10.62 ✔

 

Award [2] for correct final answer.

Accept answers for M2 between 10.6 and 10.7.

Award [1 max] for pH = 10.02.

Syllabus sections