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Edexcel A-Level Chemistry AS 6.8 Evaluate the Results Obtained From Experiments and Comment on Sources of Error and Uncertainty and Any Assumptions Made Questions

Use Edexcel IAL Chemistry questions to extrapolate temperature changes, assess assumptions and apparatus, explain data-book differences, and suggest improvements to calorimetry methods.

Syllabus
First assessment 2019
Course
Chemistry YCH11
Level
AS

Exam points

  • Use temperature–time graphs and extrapolation to determine maximum temperature change.
  • Evaluate assumptions, apparatus and procedure choices that affect calorimetry accuracy.
  • Explain discrepancies from data-book enthalpy using heat loss, combustion, evaporation and heat-capacity effects.

Edexcel A-Level Chemistry AS 6.8 Evaluate the Results Obtained From Experiments and Comment on Sources of Error and Uncertainty and Any Assumptions Made Questions question 1

[Maximum number: 2]

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 Edexcel A-Level Chemistry AS 6.8 Evaluate the Results Obtained From Experiments and Comment on Sources of Error and Uncertainty and Any Assumptions Made Questions 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, C2H5OH\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}, a student used the apparatus shown.

Figure for Question Edexcel A-Level Chemistry AS 6.8 Evaluate the Results Obtained From Experiments and Comment on Sources of Error and Uncertainty and Any Assumptions Made Questions question 1 — Edexcel A-Level Chemistry AS

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

The student looked in a data book and found the actual value for the standard enthalpy change of combustion of ethanol was more exothermic than the experimental value obtained.

Give two reasons for the difference between the data book value and the experimental value, other than referring to standard conditions.

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