A technician compares the volume of oxygen made when hydrogen peroxide solution decomposes in the presence of manganese dioxide. Fig. 1 shows oxygen being c...
Question 1 Report
A technician compares the volume of oxygen made when hydrogen peroxide solution decomposes in the presence of manganese dioxide. Fig. 1 shows oxygen being collected over water. The delivery tube is placed under an inverted measuring cylinder so that the gas displaces water. The same mass of manganese dioxide and the same volume and concentration of hydrogen peroxide solution are used in each trial.
Table 1 shows the total volume of gas collected.
| Time / s | Volume of oxygen / cm3 |
|---|---|
| 0 | 0 |
| 30 | 18 |
| 60 | 36 |
| 90 | 42 |
| 120 | 42 |
(a) Name the gas collected in the measuring cylinder. [1]
(b) State the test for this gas and the positive result. [2]
(c) Use Table 1 to calculate the mean rate of gas production between 30 s and 90 s. [3]
(d) Explain why the volume stays at 42 cm3 after 90 s. [2]
(e) Complete the balanced equation for the reaction.
_____H2O2 → _____H2O + _____O2 [2]
(f) Give two reasons why water is suitable for collecting oxygen in this apparatus. [2]
Answer Details
(a) The collected gas is oxygen. Hydrogen peroxide decomposes in the presence of manganese dioxide, which acts as a catalyst. [1]
(b) Insert a glowing splint into the gas. A positive result is that the splint relights (rekindles). This is the characteristic test for oxygen. [2]
(c) Mean rate means volume produced divided by the time taken.
\[\text{volume made}=42-18=24\text{ cm}^3\]
\[\text{time interval}=90-30=60\text{ s}\]
\[\text{mean rate}=\frac{24}{60}=0.40\text{ cm}^3\text{ s}^{-1}\]
The mean rate is 0.40 cm3 s-1. [3]
(d) By 90 s, all the hydrogen peroxide has reacted. Therefore, no more oxygen is produced, so there is no further gas to displace water and the volume remains 42 cm3. [2]
(e) The balanced equation is:
\[2\mathrm{H_2O_2}\rightarrow2\mathrm{H_2O}+\mathrm{O_2}\]
This conserves four hydrogen atoms and four oxygen atoms on each side. [2]
(f) Water is suitable because oxygen is only slightly soluble in water, so little is lost by dissolving, and oxygen does not react with water. [2]
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