Edexcel IAL Chemistry 6.P5 measurement uncertainties and errors

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

Exam points

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.

[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 $250.0 \mathrm{~cm}^{3}$ in a volumetric flask.

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

Assume two weighings are needed.

±0.0025 g

±0.005 g

±0.01 g

±0.05 g

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6.P5—Uncertainties and errors question 1