Fig. 6.1 shows the apparatus a student used to measure the volume of gas given off when a piece of magnesium ribbon reacts with dilute sulfuric acid. Fig. 6...
Question 1 Report
Fig. 6.1 shows the apparatus a student used to measure the volume of gas given off when a piece of magnesium ribbon reacts with dilute sulfuric acid.
Fig. 6.1
(a) Name the piece of apparatus labelled Y, which is used to measure the volume of gas. [1]
(b) Name the gas given off and describe the test and result used to confirm it. [2]
(c) Describe how the student would use this apparatus together with a stop-clock to follow the rate of the reaction. [2]
(d) Some gas escapes before the bung, labelled X, is pushed into the flask. State how this affects the total volume of gas recorded and why. [2]
(e) Suggest one change to the method that would reduce this loss of gas. [1]
Answer Details
This tests following a reaction rate by collecting a gas and understanding how lost gas affects the reading. Magnesium and dilute sulfuric acid give hydrogen: \[\text{Mg} + \text{H}_2\text{SO}_4 \rightarrow \text{MgSO}_4 + \text{H}_2\]
(a) The apparatus labelled Y, which collects and measures the volume of gas, is a gas syringe. [1]
(b) The gas given off is hydrogen. [1] To test it, hold a lighted splint at the mouth of the tube; hydrogen burns with a squeaky pop. [1]
(c) To follow the rate: start the stop-clock at the moment the acid and magnesium are mixed. [1] Then read and record the volume of gas in the syringe at regular time intervals, for example every \(30\ \text{s}\). [1] Plotting volume against time then shows how fast the gas is produced.
(d) If gas escapes before the bung X is in place, the total volume recorded is smaller than the true volume. [1] This is because that early gas is never collected in the syringe, so it is missing from the final reading. [1]
(e) One improvement, for example add the magnesium and replace the bung as quickly as possible, or use a flask with a side arm so the bung is already fitted before the reaction starts. [1]
Exam tip: any gas lost before collection always makes the measured volume too low, never too high.
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