Edexcel IAL Chemistry Measurement Uncertainty

Practise Edexcel IAL Chemistry measurement uncertainty through burette, thermometer and balance readings, percentage uncertainty and ways to reduce it.

Exam points

Double reading uncertainties for temperature changes or titres before calculating percentage uncertainty.
Work backwards from percentage uncertainty to a titre, or state balance ranges from two mass readings.
Explain how increasing the measured change reduces percentage uncertainty without changing apparatus.

[Maximum number: 1]

Fuels

Fuels burn in oxygen to release a lot of energy.
Many hydrocarbons and alcohols are used as fuels. During complete combustion, they produce carbon dioxide and water.

Petrol contains 2,2,4-trimethylpentane, an isomer of octane, that promotes smooth combustion.

Figure for Question B.1.3—Measurement uncertainty question 1 — Edexcel A-Level Chemistry AS

2,2,4-trimethylpentane

Alcohols, such as methanol and ethanol, can be used as fuels either on their own or as additives in petrol.

In an experiment to determine the enthalpy change of combustion of ethanol, $\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}$ , a student used the apparatus shown.

Results:
Mass of water $=100.0 \mathrm{~g}$
Mass of ethanol used $=0.305 \mathrm{~g}$
Temperature rise of water $=13.2^{\circ} \mathrm{C}$

The uncertainty in each thermometer reading is $\pm 0.05^{\circ} \mathrm{C}$ .

Calculate the percentage uncertainty in the temperature rise in this experiment.

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B.1.3—Measurement uncertainty question 1