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AQA · GCSE · Chemistry · Higher

Concentration effect graph sketch

Q09.4 2 marks

Figure 13 shows the results for 0.40 mol/dm³ sulfuric acid. The student repeated the experiment using 0.20 mol/dm³ sulfuric acid instead of 0.40 mol/dm³ sulfuric acid. Excess zinc was used in each experiment.

Sketch a line on Figure 13 to show the results you would expect.

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Marking points

  1. 1 The new curve begins at the origin and has a smaller initial gradient than the 0.40 mol/dm³ curve.
  2. 2 The new curve plateaus at 0.0084 mol within the stated tolerance.

Why this answer loses marks

The new curve is less steep but reaches the same plateau.

Lower acid concentration slows the reaction and, because zinc is in excess, also reduces the total hydrogen produced.