The diagram shows an experiment used by a student to prepare small samples of hydrogen and oxygen from acidified water. Dilute sulfuric acid is added only t...
Question 1 Report
The diagram shows an experiment used by a student to prepare small samples of hydrogen and oxygen from acidified water. Dilute sulfuric acid is added only to improve electrical conductivity. Platinum electrodes are connected to a low-voltage supply. After 15 minutes, the measuring tubes contain different volumes of gas. The student records the volumes before carrying out gas tests away from the power supply.
(a) Name the gas in the 48 cm3 tube and name the gas in the 24 cm3 tube. [2]
(b) Give a test, including the observation, for the gas in the 24 cm3 tube. [2]
(c) Use the diagram to calculate the total volume of gas collected in 15 minutes and calculate the mean total rate of gas collection in cm3 per minute. [3]
(d) Complete the balanced equation for this reaction: 2H2O → ........H2 + ........O2 [3]
(e) Explain why dilute sulfuric acid is added but is not used up overall. [2]
(f) State two safety precautions for this experiment. [2]
Answer Details
(a) The \(48\ \mathrm{cm^3}\) tube contains hydrogen and the \(24\ \mathrm{cm^3}\) tube contains oxygen. This matches the expected 2:1 volume ratio. [2]
(b) Test oxygen using a glowing splint. The glowing splint relights. [2]
(c)
\[48\ \mathrm{cm^3}+24\ \mathrm{cm^3}=72\ \mathrm{cm^3}\]
\[\text{mean total rate}=\frac{72\ \mathrm{cm^3}}{15\ \mathrm{min}}=4.8\ \mathrm{cm^3\ min^{-1}}\]
[3]
(d)
\[\mathrm{2H_2O\rightarrow2H_2+O_2}\]
There are four hydrogen atoms and two oxygen atoms on both sides. [3]
(e) Dilute sulfuric acid provides ions, allowing the water to conduct electricity. It is not a reactant in the overall equation, so it is unchanged overall. [2]
(f) Suitable safety precautions include using a low-voltage supply, wearing eye protection, keeping flames away from hydrogen, and switching off the supply before handling electrodes. Any two gain [2].
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