Some students investigated the rate of decomposition of hydrogen peroxide, H₂O₂ - AQA - GCSE Chemistry - Question 9 - 2019 - Paper 2
Question 9
Some students investigated the rate of decomposition of hydrogen peroxide, H₂O₂.
The equation for the reaction is:
$$2H_2O_2(aq) \rightarrow 2H_2O(l) + O_2(g)$$
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Worked Solution & Example Answer:Some students investigated the rate of decomposition of hydrogen peroxide, H₂O₂ - AQA - GCSE Chemistry - Question 9 - 2019 - Paper 2
Step 1
Describe a test to identify the gas produced in the reaction.
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Answer
To identify the gas produced in the reaction, a glowing splint can be used. If the gas is oxygen, the glowing splint will relight, indicating the presence of oxygen.
Step 2
What two improvements could student A make to the method to give valid results?
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Answer
Measure the volume of gas produced every 2 minutes.
Place the conical flask in a water bath at constant temperature.
Step 3
Determine the mean rate of reaction in cm³/s between 2 and 4 minutes for coarse manganese dioxide lumps.
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Answer
From Figure 9, at 2 minutes, the volume of gas produced is 11 cm³, and at 4 minutes, it is 20 cm³. The difference in volume is:
20extcm3−11extcm3=9extcm3
The time interval is 120 seconds (from 2 to 4 minutes). Thus, the mean rate of reaction is:
Mean rate of reaction=120 s9 cm3=0.075 cm3/s
Rounding to two significant figures gives 0.08 cm³/s.
Step 4
Sketch on Figure 9 the curve you would expect to see.
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The curve for the reaction with the 0.2 mol/dm³ hydrogen peroxide should start at the origin and level off at around 40 cm³, showing a slower rate of reaction compared to the curve for the 0.3 mol/dm³ hydrogen peroxide.
Step 5
Explain why the rate of reaction is different when manganese dioxide is used as a fine powder rather than coarse lumps.
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The surface area of fine manganese dioxide powder is greater compared to coarse lumps. This increased surface area allows for more collisions between hydrogen peroxide molecules and manganese dioxide particles per unit time, resulting in a higher rate of reaction.
