SC14e Molar Volumes of Gases - Higher

Question 1

14.9 describe the molar volume, of any gas at room temperature and pressure, as the volume occupied by one mole of molecules of any gas room temperature and pressure

Question 2

14.10 use the molar volume and balanced equations and calculations involving the masses of solids and volume of gases.

Question 3

14.11 use avogadro’s law to calculate volumes of gases involved in a gaseous reaction, given relevant equation

Question 4

What is the molar volume of any gas at room temperature and pressure?

Answer 4

24dm3

Question 5

Why does the volume of gas are not depend on its relative formula mass?

Answer 5

Because the mean distance between the gas particles is very large compared to the size of the particles

Question 6

practical - how can you measure the molar volume of a gas

Answer 6

1. clamp a gas syringe onto a stand and put the delivery tube in a conical flask.
2. Add 50cm3 of dilute hydrochloric acid to the conical flask and reconnect the bung
3. Measure and record the mass of the piece of the magnesium ribbon. It should be no more than 0.09g
4. Remove the bung add the magnesium to the acid and immediately reconnect the bung
5. Swirl the flask carefully to mix its contents
6. When the reaction is complete, record the volume of gas collected in the gas syringe

Question 7

calculate the volume occupied by 1 mol of gas when 0.08g mg was used and 79.2cm3 of hydrogen was collected
Mg(s) + 2HCl(aq) → MgCl2(aq) + H2

Answer 7

calculate mol of magnesium
mass/mr = 0.08/24 = 0.0033
use ratio to find mols of hydrogen produced
Mg : H2 = 1 : 1 so moles of H2 = 0.0033
1/0.0033 x 79.2 = 23800cm3

Question 8

explain 3 sources of error that could of happened in the practical.

Answer 8

1. Gas gas was lost between the start of the reaction and replacing the bung
2. Gas syringe doesn’t start at 0cm3
3. Precision of equipment; balance and gas syringe

Question 9

Sodium react of chlorine to form sodium chloride:
2Na + Cl2 → 2NaCl
Calculate the minimum volume at rtp, dm3, of chlorine needed to react completely with 0.92g of sodium.

Answer 9

amount of sodium = 0.92/23 =0.040mol
ratio = 2 mol of Na : 1 mol of Cl2
0.04mol Na : 0.02mol Cl2
volume of Cl2 = 0.02 x 24 = 0.48dm3

Question 10

volume of gas =

Answer 10

amount in mol x molar volume (24dm3 or 24000cm3)

Question 11

sodium reacts with chlorine to form sodium chloride:
2Na(s) + Cl2(g) → 2NaCl(s)
calculate the maximum mass of sodium chloride that can be made from 960cm3 of chlorine at rtp and an excess of sodium

Answer 11

amount of chlorine = 90/24000 = 0.040mol
1 mol of Cl2 : 2 mol of NaCl
so 0.040mol of Cl2 : 0.080mol of NaCl
mass of NaCl = 0.080 x 58.5 = 4.68g

Question 12

copper carbonate decomposes when heated:
CuCO3(s) → CuO(s) + CO2(g)
calculate the minimum mass of copper carbonate needed to produce 1.44dm3 of carbon dioxide at rtp

Answer 12

amount of carbon dioxide = 1.44/24 = 0.060 mol
1 mol of CO2 : 1 mol of CuCO3
so 0.060 mol of CO2 : 0.060 mol of CuCO3
mas of CuCO3 = 0.060 x 123.5 = 7.41g

Question 13

Silicon reacts with hot, concentrated sodium hydroxide solution to produce sodium silicate and hydrogen.​
Si(S) + 4NaOH(aq) → Na4SiO4(s) + 2H2(g)​
Calculate the minimum mass of silicon needed to produce 1000dm3 of hydrogen at rtp. (2 marks)

Answer 13

Mol H2 = 1000/24 = 41.67mol (1)​

Mol Si = 41.67/2 = 20.83mol​

Mass Si = 20.83 x28 = 538g (1)