Changing the concentration of the reactants

3 marks · Normal

In an experiment, a student finds that 0.21 g of carbon dioxide are released in the first 30 seconds of a reaction between marble chips and hydrochloric acid. Calculate the average rate of reaction (in g/s) during this time. Show your working.

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Show answer

0.007 g/s (±0.001)

Common mistakes: Dividing 30 by 0.21 instead of 0.21 by 30

Show mark scheme and worked solution

Marking points

M1 · 1 mark · States/formulates the correct method: rate = mass lost / time. (follow-through)

M2 · 1 mark · Substitutes correct values (0.21 and 30). (follow-through)

A1 · 1 mark · Correct final answer: 0.007 g/s (allow rounding to 0.0070 or 0.007). (follow-through)

Worked solution

Average rate = mass lost / time