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CAIE A-Level Chemistry AS P3.8 Errors Uncertainty Improvements and Extensions Questions

Practise evaluating systematic and random errors, uncertainty and realistic improvements to experimental methods.

Syllabus
2028–2030
Course
Chemistry 9701
Level
AS

Exam points

  • identify significant sources of systematic and random error
  • state actual or percentage uncertainty appropriately
  • suggest realistic modifications that improve accuracy

CAIE A-Level Chemistry AS P3.8 Errors Uncertainty Improvements and Extensions Questions question 1

[Maximum number: 1]

The reaction between Na2 S2O3(aq)\mathrm{Na}_{2} \mathrm{~S}_{2} \mathrm{O}_{3}(\mathrm{aq}) and HCl(aq) is monitored at constant temperature.

Na2 S2O3+2HCl→2NaCl+SO2+S+H2O\mathrm{Na}_{2} \mathrm{~S}_{2} \mathrm{O}_{3}+2 \mathrm{HCl} \rightarrow 2 \mathrm{NaCl}+\mathrm{SO}_{2}+\mathrm{S}+\mathrm{H}_{2} \mathrm{O}

Fig. 4.1 shows how the concentration of HCl(aq) varies with time.

Fig. 4.1

Fig. 4.1

Explain why the rate of reaction cannot be monitored accurately by measuring the volume of SO2( g)\mathrm{SO}_{2}(\mathrm{~g}) produced in this reaction.

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