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Edexcel IAL Chemistry Substitution into Equations

Practise Edexcel IAL Chemistry substitution into algebraic equations through enthalpy, energy density, concentration and multi-step mole calculations.

Syllabus
Pearson Edexcel International Advanced Subsidiary/Advanced Level
Course
Chemistry XCH11/YCH11
Level
A2

Exam points

  • Substitute gradients into relationships such as gradient = -H/R and report enthalpy with correct units.
  • Combine density, percentage by volume and molar mass steps to calculate moles in multi-stage problems.
  • Use previous calculated values in energy or electrode equations, carrying units through to the final answer.

B.2.3—Substitution into algebraic equations question 1

[Maximum number: 1]

This question is about electrochemical cells.

The Direct Methanol Fuel Cell (DMFC) uses methanol and oxygen to generate electricity. When the cell operates, the methanol reacts with water at one electrode to produce carbon dioxide and hydrogen ions.
At the other electrode the oxygen reacts with hydrogen ions to form water.

The reduction half-cell in the DMFC has a standard electrode potential E⊖=+1.23 VE^{\ominus}=+1.23 \mathrm{~V}.
When the solution concentration changes, the electrode potential changes so that E=+1.20 VE=+1.20 \mathrm{~V}.
The relationship between these values is given by the equation

E=E⊖+4.277×10−3ln⁡XE=E^{\ominus}+4.277 \times 10^{-3} \ln \mathbf{X}

where X is the concentration of the solution in moldm−3\mathrm{mol} \mathrm{dm}^{-3}.
Calculate the value of X in the non-standard half-cell.

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