3.5 Amount of Substance & Gas Volume

This question is about combustion.

A 0.050 mol sample of a hydrocarbon was burned in excess oxygen.

To determine the identity of the hydrocarbon, the type of combustion used is important.

Which type of combustion should be used to determine the identity of the hydrocarbon? Explain your reasoning.

3.6 dm³ of carbon dioxide were produced during the complete combustion of the 0.050 mol sample of a hydrocarbon.

Calculate the number of moles of carbon dioxide released.

When the hydrocarbon was burned 1.204 x 10²³ molecules of water were produced. 

Calculate the number of moles of hydrogen atoms in 1.204 x 10²³ molecules of water.

The amount of hydrocarbon burned was 0.050 mol.

Calculate the molecular formula of the hydrocarbon.

Sodium carbonate reacts with dilute hydrochloric acid:

Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂

A student investigated the volume of carbon dioxide produced when different masses of sodium carbonate were reacted with dilute hydrochloric acid.

This is the method used.

1. Place a known mass of sodium carbonate in a conical flask.
2. Measure 10 cm³ of dilute hydrochloric acid using a measuring cylinder.
3. Pour the acid into the conical flask.
4. Place a bung in the flask and collect the gas until the reaction is complete.

The student has set the apparatus incorrectly as shown in Figure 1.

Figure 1

Identify the error and describe what would happen if the student used the apparatus.

The student corrected the error and collected the results shown in Table 1.

Table 1

Suggest why the volume of carbon dioxide collected reaches a maximum of 95.0 cm³.

Describe how the student could accurately determine the minimum mass of sodium carbonate required to produce 95.0 cm³ of carbon dioxide.

The carbon dioxide was collected at room temperature and pressure. 

Calculate the number of atoms of oxygen present in the 95.0 cm³ of carbon dioxide produced. 

Give your answer to three significant figures.

This question is about the reduction of tungsten oxide, WO₃.

A teacher reduces tungsten oxide to tungsten using the following method and the equipment shown in Figure 1.

• Record the mass of the weighing boat
• Add tungsten oxide and record the mass again
• Heat the weighing boat and tungsten oxide strongly for two minutes and then allow to cool
• Record the mass of the weighing boat and its contents

Figure 1

Write the balanced symbol equation, including state symbols, for the reduction of tungsten oxide by hydrogen.

State one addition to the method to check that the tungsten oxide has been completely reduced.

In industry, tungsten oxide is reduced on a large scale using hydrogen.

Using your equation from part (a), calculate the minimum volume, in dm³, of hydrogen that is required to react with 13.92 tonnes of tungsten oxide. 

Relative atomic masses (A_r):     W = 184,     O = 16,     H = 1 

1 tonne = 1 x 10⁶ g

This question is about power stations.

Coal-fired power stations are being phased out as the supply of coal decreases and greater restrictions on emissions are implemented.

Coal typically contains between 0.2% and 5% sulfur by dry weight.

Calculate the average number of moles of sulfur in 75 tonnes of coal. 

Relative atomic mass (A_r):     S = 32

1 tonne = 1 x 10⁶ g

Calculate the volume of sulfur dioxide released from the combustion of 75 tonnes of typical coal.

Natural gas is replacing coal in some power stations. 

The typical sulphur content of natural gas is 5.5 x 10^–6 g / dm³. 

An articulated fuel tanker truck can carry up to 36000 dm³ of natural gas. 

Calculate the volume, in cm³, of sulfur dioxide that could be released by combusting the 36000 dm³ of natural gas carried in the tanker truck.

A student investigated the electrolysis of a solution of sodium chloride by measuring how the volume of gases produced changes with time.

Figure 1 shows the apparatus used in the investigation.

Figure 1

The student made an error in designing and setting up the apparatus for this investigation.

Identify the error and suggest what needs to be changed.

The student soon adjusted the apparatus and was able to perform the investigation correctly. 

The student measured the volumes of gases produced every minute for 20 minutes and constructed a graph of these results.

Figure 2 shows the graph of the investigation.

Figure 2

Using the graph, describe the trends shown in the results.

The number of moles of each gas produced at each electrode is the same and no gas escapes from the apparatus however there is a difference in the amount of gas collected.

Suggest one reason for the difference in volume of each gas collected.

Using Figure 2, calculate the amount in moles of chlorine collected after 16 minutes.

The volume of one mole of any gas at room temperature and pressure is 24.0 dm³

State your answer in standard form.

Air bags are designed to protect car passengers in the event of an accident. 

Crash sensors in the car detect an impact and immediately heat a small container with a mixture of chemicals. 

The heat produced triggers a chemical reaction which produces nitrogen gas. 

The gas fills the bag which provides the cushion needed for protection.

Figure 1 demonstrates this process.

The chemical mix contains sodium azide (NaN₃) which undergoes thermal decomposition to form sodium and nitrogen.

The equation for the reaction is:

2NaN₃       →       2Na       +       3N₂

A typical air bag contains around 143 g of sodium azide.

Calculate the mass of nitrogen produced when 143 g of sodium azide decomposes.

Relative atomic masses (A_r): N = 14; Na = 23

1 g of nitrogen has a volume of 0.86 litres at room temperature and pressure.

What volume of nitrogen would be produced from 143 g of sodium azide?

(If you did not answer part (a), assume that the mass of nitrogen produced from 143 g of sodium azide is 85 g. This is not the correct answer to part a))

State the conditions of temperature and pressure at r.t.p.

This question is about calculating the volumes of gases produced in different reactions.

What volume of hydrogen is produced from the reaction of 2.5 g of magnesium with excess sulfuric acid?

Mg   +   H₂SO₄  →   MgSO₄  +   H₂ 

Relative atomic mass (A_r): Mg = 24

What volume of steam is produced from the combustion of 2.000 kg of methane in excess oxygen?

CH₄    +    2O₂     →    CO₂     +     2H₂O 

Relative formula mass (M_r): CH₄ = 16

What mass of iodine is required to react with hydrogen to produce 67.20 dm³ of hydrogen iodide?

I₂    +    H₂     →    2 HI

Relative atomic mass (A_r): I = 127