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Edexcel IAL Chemistry A2 6.P5 measurement uncertainties and errors

Edexcel IAL Chemistry A2 6.P5 measurement uncertainties and errors
Pearson Edexcel IAL Chemistry syllabusChemistry YCH11First assessment 2019

Use the apparatus data carefully: combine repeated reading uncertainty, compare percentage uncertainty and decide whether the actual measured value can still be plotted.

How this is tested

  • Calculate percentage uncertainty from two thermometer readings and a temperature change.
  • Explain why the largest measured volume has the lowest percentage uncertainty.
  • Decide whether an off-target reagent volume can still be used when the actual value is plotted.

Question 12(a)

[Maximum number: 1]

Sodium thiosulfate can be used to determine the concentration of an iodine solution by titration using starch indicator.

5.00 g of sodium thiosulfate was dissolved in deionised water and the solution made up to 250.0 cm3250.0 \mathrm{~cm}^{3} in a volumetric flask.

The volumetric flask has an uncertainty of ±0.25 cm3\pm 0.25 \mathrm{~cm}^{3}.
What is the minimum uncertainty of the balance required to match the uncertainty of the volumetric flask?

Assume two weighings are needed.

A

±0.0025 g\pm 0.0025 \mathrm{~g}

B

±0.005 g\pm 0.005 \mathrm{~g}

C

±0.01 g\pm 0.01 \mathrm{~g}

D

±0.05 g\pm 0.05 \mathrm{~g}