Some students investigated the effect of temperature on the rate of reaction. The students reacted sodium thiosulfate solution with hydrochloric acid. This is the method used. 1. Use a beaker to measure 50 cm³ of heated sodium thiosulfate solution into a conical flask. 2. Measure the temperature of the room. 3. Put the conical flask on a black cross drawn on a piece of paper. 4. Start a timer. 5. Use the same beaker to measure 10 cm³ of hydrochloric acid into the conical flask. 6. Stop the timer when the cross is no longer visible. The students repeated the experiment at a different room temperature. **Figure 1** shows the apparatus. The method contains errors and does not produce accurate results. Describe a method the students should use to produce accurate results. You do not need to write about safety precautions. Some students investigated the effect of temperature on the rate of a different reaction. They recorded the loss of mass from their apparatus at 40 °C. **Figure 2** shows the results.

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Some students investigated the effect of temperature on the rate of reaction - AQA - GCSE Chemistry Combined Science - Question 2 - 2020 - Paper 2

Question 2

Some students investigated the effect of temperature on the rate of reaction. The students reacted sodium thiosulfate solution with hydrochloric acid. This is the m... show full transcript

Worked Solution & Example Answer:Some students investigated the effect of temperature on the rate of reaction - AQA - GCSE Chemistry Combined Science - Question 2 - 2020 - Paper 2

Step 1

Describe a method the students should use to produce accurate results.

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Answer

To enhance the accuracy of the reaction measurement, the following steps should be taken:

Use Precise Measuring Equipment: Instead of a beaker, utilize a measuring cylinder or a burette to measure 50 cm³ of sodium thiosulfate, ensuring the measurement is accurate.
Control Temperature: Implement a thermostat to maintain the temperature of the sodium thiosulfate solution to a constant 50 °C before mixing, recording the exact temperature with a thermometer.
Standardize the Setup: Place the conical flask directly above the black cross on a flat surface where variables, such as light, do not affect visibility.
Timing Accuracy: Utilize a digital stopwatch to monitor time precisely when the hydrochloric acid is added, ensuring accurate timing of the reaction.
Monitor Reaction Temperature: Measure the temperature of the solution immediately after the hydrochloric acid is added and record it. This step is crucial to ensure fluctuations in temperature do not affect reaction time.
Multiple Trials: Repeat the experiment at least three times for each temperature to obtain an average reaction time, accounting for anomalies.
Record Final Temperature: Measure the temperature of the solution at the end of the reaction to assess any temperature changes during the experiment.

Step 2

Calculate the mean rate of reaction between 1 minute and 3 minutes at 40 °C

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Answer

To calculate the mean rate of reaction:

Identify the Change in Mass: From Figure 2, find the mass loss at 1 minute and 3 minutes. The change in mass from the graph is:
- At 1 minute: -0.15 g
- At 3 minutes: -0.30 g
- Therefore, the change in mass is: $Change = (-0.30 g) - (-0.15 g) = -0.15 g$
Determine the Time Period: The time difference between 1 minute and 3 minutes is:
- $Time = 3 ext{ min} - 1 ext{ min} = 2 ext{ min}$
Apply the Formula: Use the equation: $ext{Mean rate of reaction} = \frac{\text{change in mass in g}}{\text{time in min}}$
Calculate the Mean Rate:
- $\text{Mean rate of reaction} = \frac{-0.15 g}{2 ext{ min}} = -0.075 ext{ g/min}$

Thus, the mean rate of reaction is approximately (-0.075) g/min.

Step 3

Draw a curve on Figure 2 for the results you would expect at a temperature of 50 °C instead of 40 °C

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In Figure 2, the curve for results at 50 °C should start at the same initial mass loss point as at 40 °C, but should decrease at a steeper rate due to the increased reaction rate at a higher temperature. Therefore, the curve should:

Begin steeply downward from the same starting point, indicating a faster rate of mass loss.
Level off at a slightly lower mass, showing a greater overall mass loss compared to the 40 °C curve over the same time interval.

This visual representation would reflect the increased reactivity due to higher temperatures.

Some students investigated the effect of temperature on the rate of reaction - AQA - GCSE Chemistry Combined Science - Question 2 - 2020 - Paper 2

Worked Solution & Example Answer:Some students investigated the effect of temperature on the rate of reaction - AQA - GCSE Chemistry Combined Science - Question 2 - 2020 - Paper 2

Describe a method the students should use to produce accurate results.

Calculate the mean rate of reaction between 1 minute and 3 minutes at 40 °C

Draw a curve on Figure 2 for the results you would expect at a temperature of 50 °C instead of 40 °C

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