Solutions of hydrogen peroxide (H₂O₂) are unstable and decompose according to the following balanced equation:
2H₂O₂ → 2H₂O + O₂
A student measured the rate of decomposition, in the presence of a catalyst, of a hydrogen peroxide solution that had been in storage for some time - Leaving Cert Chemistry - Question 3 - 2022
Question 3
Solutions of hydrogen peroxide (H₂O₂) are unstable and decompose according to the following balanced equation:
2H₂O₂ → 2H₂O + O₂
A student measured the rate of dec... show full transcript
Worked Solution & Example Answer:Solutions of hydrogen peroxide (H₂O₂) are unstable and decompose according to the following balanced equation:
2H₂O₂ → 2H₂O + O₂
A student measured the rate of decomposition, in the presence of a catalyst, of a hydrogen peroxide solution that had been in storage for some time - Leaving Cert Chemistry - Question 3 - 2022
Step 1
Identify a suitable catalyst for the decomposition of H₂O₂.
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Answer
The suitable catalyst for the decomposition of hydrogen peroxide (H₂O₂) is manganese(IV) oxide (MnO₂).
Step 2
Describe the appearance of the catalyst.
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Answer
The appearance of manganese(IV) oxide is a black or brown powder, often found in fine particles, or as small pieces of larger grains or stems.
Step 3
Explain how the catalyst could have been added to the hydrogen peroxide solution in the flask without loss of oxygen gas.
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The catalyst can be added to the hydrogen peroxide solution using a small test tube inverted in the flask. This allows the catalyst to fall into the flask without disturbing the gel, thereby minimizing the loss of oxygen gas.
Step 4
Plot a graph (on graph paper) of volume of O₂ (y-axis) versus time.
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In the graph, the y-axis will represent the volume of oxygen (cm³) and the x-axis will represent the time (minutes). The points will be plotted based on the data given in the table.
Step 5
Estimate the time taken to collect 50 cm³ of oxygen.
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Answer
From the graph, the estimated time to collect 50 cm³ of oxygen is approximately between 1 minute and 2 minutes, around 1.3 minutes.
Step 6
Find the average rate of reaction over the first 2.5 minutes (in cm³ of O₂ per minute).
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Answer
The volume of oxygen produced at 2.5 minutes is between 68 cm³ and 76 cm³. Thus, taking an average, we can calculate:
Average Rate = ( \frac{76 - 37.5}{2.5 - 0} = \frac{38.5}{2.5} = 15.4 ) cm³ per minute.
Step 7
State and explain whether the solution had fully or partially decomposed during storage.
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The solution had partially decomposed during storage. This is supported by the fact that only 98 cm³ of oxygen was produced instead of the expected 250 cm³, indicating some loss of oxygen due to incomplete decomposition.
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