DP Chemistry (last assessment 2024)

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Question 21N.2.sl.TZ0.b

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Date November 2021 Marks available [Maximum mark: 2] Reference code 21N.2.sl.TZ0.b
Level sl Paper 2 Time zone TZ0
Command term Determine Question number b Adapted from N/A
b.
[Maximum mark: 2]
21N.2.sl.TZ0.b

Biochemical oxygen demand (BOD) can be determined by the Winkler Method.

A student dissolved 0.1240 ± 0.0001 g of Na2S2O3 to make 1000.0 ± 0.4 cm3 of solution to use in the Winkler Method.

Determine the percentage uncertainty in the molar concentration.

[2]

Markscheme

«0.0001 g0.1240 g×100%=» 0.08 «%»
OR
«0.4 cm31000.0 cm3×100%=» 0.04 «%» ✔


«0.08 % + 0.04 % =» 0.12/0.1 «%» ✔


Award [2] for correct final answer.

Accept fractional uncertainties for M1, i.e., 0.0008 OR 0.0004.

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