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AQA GCSE · Question 07.5 · The rate and extent of chemical change
Figure 7 shows results of the experiment with the hydrochloric acid of a higher concentration. Calculate the mean rate of reaction between 0 and 50 seconds. Use Figure 7 and the equation:
mean rate of reaction = mean volume of gas collected / time taken
Figure 7 shows results of the experiment with the hydrochloric acid of a higher concentration. Calculate the mean rate of reaction between 0 and 50 seconds. Use Figure 7 and the equation:
mean rate of reaction = mean volume of gas collected / time taken
How to approach this question
1. Find the time of 50 seconds on the x-axis.
2. Use a ruler to draw a line vertically up from 50 seconds to the curve.
3. From that point on the curve, draw a line horizontally across to the y-axis.
4. Read the value on the y-axis. This is the "mean volume of gas collected".
5. The "time taken" is 50 seconds.
6. Substitute the volume and time into the given equation and calculate the rate.
Full Answer
From graph, at 50 seconds, volume of gas = 70 cm³.
Time taken = 50 s.
Mean rate = 70 cm³ / 50 s
Mean rate = 1.4 cm³/s
The question asks for the mean rate of reaction between 0 and 50 seconds.
First, we need to find the volume of gas collected at 50 seconds from the graph in Figure 7.
1. Locate 50 s on the x-axis (midway between 40 and 60).
2. Follow the line up to the curve.
3. Follow the line across to the y-axis. The value is exactly on the line for 70 cm³.
So, the volume of gas collected is 70 cm³.
The time taken is 50 s.
Now, use the equation:
mean rate of reaction = mean volume of gas collected / time taken
mean rate of reaction = 70 cm³ / 50 s
mean rate of reaction = 1.4 cm³/s
Common mistakes
✗ Misreading the graph.
✗ Dividing time by volume instead of volume by time.
✗ Calculation errors.
Practice the full AQA GCSE Chemistry Foundation Tier Paper 2
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