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Molar Volume of Gases

Section A

1. 10 cm3 of a gaseous hydrocarbon needed 30 cm3 of oxygen for complete combustion and 20 cm3 of carbon dioxide were produced. What is the molecular formula of the hydrocarbon?

B C2H2
C C2H4
D C2H6

2. What mass of iodine will be produced if 200 cm3 of chlorine gas is passed into 100 cm3 of 0.2 mol dm-3 potassium iodide solution, at 20 oC and a pressure of one atmosphere?
A 1.06 g
B 2.12 g
C 2.54 g
D 5.08 g

3. 10 cm3 of a gas G were mixed with 100 cm3 (an excess) of oxygen in a sealed container at 20 oC and one atmosphere pressure. The gas was then ignited electrically and burned completely in the oxygen. After the reaction the volume of the gas mixture, measured at the same temperature and pressure, was found to be 105 cm3. Which one of the following was G?
A Methane, CH4
B Hydrogen, H2
C Carbon monoxide, CO
D Ethene, C2H4

Section B

Carbon dioxide is a molecular substance. It has properties characteristic of a molecule with low molecular mass. Water dissolves about 1.75 times its own volume of carbon dioxide at 20 oC and a pressure of one atmosphere. Solutions of carbon dioxide are weakly acidic and this can explain why carbon dioxide is used in the preparation of effervescent drinks such as lemonade.

(a) (i) Calculate the relative molecular mass of carbon dioxide. [1]

(ii) The word “relative” means that the mass is compared with something else. What is the mass of carbon dioxide compared with and why? [2]

(iii) Calculate the mass of carbon dioxide dissolved in 150 cm3 of water at 20 oC and atmospheric pressure.
(One mole of any gas occupies a volume of 24 dm3 at 20 oC and a pressure of one atmosphere.) [2]

(iv) Use this value to calculate the molarity of the solution. [2]