The diagram shows a portable gas generator used by a field team to produce carbon dioxide for calibrating an air-quality sensor. Marble chips, which are mai...
Question 1 Report
The diagram shows a portable gas generator used by a field team to produce carbon dioxide for calibrating an air-quality sensor. Marble chips, which are mainly calcium carbonate, are placed in the flask. Dilute nitric acid is added through the funnel. The gas is dried before entering a calibrated collection tube.
(a) Give the formula of nitric acid. [1]
(b) Complete the balanced equation for the reaction.
CaCO3 + 2HNO3 → Ca(NO3)2 + ........ + CO2 [1]
(c) State why the gas is passed through a drying tube before its volume is measured. [1]
(d) Calculate the amount, in moles, of calcium carbonate in 5.00 g of marble chips. Assume the chips are pure CaCO3. Mr(CaCO3) = 100. [2]
(e) Use the equation to calculate the mass of carbon dioxide made from 5.00 g of calcium carbonate. Mr(CO2) = 44. [3]
(f) Suggest why large marble chips are safer than powdered calcium carbonate for this gas generator. [3]
Answer Details
(a) Nitric acid is HNO3 [1].
(b) \[\mathrm{CaCO_3+2HNO_3\rightarrow Ca(NO_3)_2+H_2O+CO_2}\] The missing product is H2O [1].
(c) The drying tube removes water vapour, so the measured volume is carbon dioxide only [1].
(d) \[n(\mathrm{CaCO_3})=\frac{5.00\text{ g}}{100\text{ g mol}^{-1}}=0.0500\text{ mol}\] [2].
(e) The equation gives a 1:1 mole ratio, so \(0.0500\) mol CaCO3 produces \(0.0500\) mol CO2 [1]. \[m=0.0500\times44=2.20\text{ g}\] [2].
(f) Large chips have less surface area than powder [1], so the reaction is slower and easier to control [1]. This reduces rapid gas production, splashing and pressure build-up [1].
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