The Mole, Avogadro & The Ideal Gas Equation (AQA A Level Chemistry)

A hydrated carbonate of an unknown Group 1 metal has the formula X₂CO₃∙10H₂O and is found to have a relative formula mass of 286. 

What is the identity of the group 1 metal?

A volume of nitrogen gas, 3.00 dm³ measured under standard conditions, was reacted with a large volume of hydrogen gas, to produce ammonia. Only 15.0% of the nitrogen gas reacted to produce ammonia.

What mass of ammonia was made?

When heated magnesium nitrate, Mg(NO₃)₂, will decompose to magnesium oxide, nitrogen dioxide and oxygen as shown. 

2Mg(NO₃₎₂ (s) →2MgO (s) + 4NO₂ (g) + O₂ (g)

8.1 g of anhydrous magnesium nitrate is heated until no further reaction takes place.

What is the mass of nitrogen dioxide produced?

Hydrogen gas is produced when 1.45 g of lithium metal reacts with water at 298 K and 100 kPa. 

2Li (s) + 2H₂O (l) → 2LiOH (aq) + H₂ (g)

Calculate the volume of hydrogen gas produced.

The gas constant, R = 8.31 J K^-1 mol^-1

Solid fertilisers often contain the elements N, P and K in a ratio of 15 g: 30 g: 15 g per 100 g of fertiliser. It is recommended that the fertiliser is used at 19 g of fertiliser per 4 dm³ of water.

What is the concentration of nitrogen atoms in the solution?

When heated, anhydrous calcium carbonate, CaCO₃, will decompose into calcium oxide and carbon dioxide as shown.

CaCO₃ (s) → CaO (s) + CO₂ (g)

1.48 g of anhydrous calcium carbonate is heated until no further reaction takes place.

What mass of carbon dioxide dioxide is produced?

0.89 g of nitrogen gas is contained in a sealed vessel of volume of 7.0 × 10^-3 m³ at a temperature of 305 K. 

What is the pressure of the vessel in Pa? 

The gas constant, R = 8.31 J K^-1 mol^-1

A compound has an M_r of 92, which contains 12 g of carbon, 2 g of hydrogen and 32 g of oxygen. What is the molecular formula of the compound? 

A student wanted to make up a 250 cm³ standard solution of anhydrous sodium carbonate, Na₂CO₃, with a concentration of 0.100 mol dm^-3. 

What is the mass of sodium carbonate they would need?

A coin contains 5.921% nickel by mass. If the coin weighs 9.97 g, how many nickel atoms are in the coin?

In a titration, 25.0 cm³ of a sodium sulfite solution required 45.0 cm³ of 0.0200 mol dm^-3 potassium manganate (VII) solution to reach the endpoint. 

2MnO₄^- (aq) + 5SO₃^2- (aq) + 6H⁺ (aq) → 2Mn²⁺ (aq) + 5SO₄^2- (aq) + 3H₂O (l)

What is the concentration of the sodium sulfite solution?

Iron and chromium can be made into an alloy called ferrochrome. Ferrochrome can be dissolved in dilute sulfuric acid to produce FeSO₄ and Cr₂(SO₄)₃. The FeSO₄ reacts with acidified K₂Cr₂O₇ as shown in the equation below:

14H⁺ + 6Fe²⁺ + Cr₂O₇^2- → 2Cr³⁺ + 6Fe³⁺ + 7H₂O

1.00 g of ferrochrome is dissolved in dilute sulfuric acid and then titrated against 13.10 cm³ of 0.100 mol dm^-3 K₂Cr₂O₇.

In the sample of ferrochrome, what is the percentage by mass of Fe?

A gas cylinder for a portable heater contains 13 kg of butane.

How many butane molecules are in the gas cylinder?

The Avogadro’s constant, L = 6.022 x 10²³ mol^-1

Bromide ions are oxidised to bromine by lead (IV) chloride. Lead (IV) chloride is reduced to lead (II) chloride.

If 6.980 g of lead (IV) chloride is added to an excess of sodium bromide solution, what mass of bromine would be produced?

2.145 g of ethanedioic acid-2-water, (COOH)₂·2H₂O, was dissolved in water and diluted to 250 cm³ in a volumetric flask. A 25.0 cm³ portion was titrated with potassium manganate (VII) solution and 35.0 cm³ was required to oxidise the acid. 

2MnO₄^- (aq) + 5C₂O₄^2- (aq) + 16H⁺ (aq) → 2Mn²⁺ (aq) + 10CO₂ (g) + 8H₂O (l)

What is the concentration of the potassium manganate (VII) solution in 25.0 cm³?

The glass containers X and Y are connected by a closed valve.

Flask Y contains ammonia, which occupies a volume of 1500 cm³. The tap is closed and there is a vacuum in flask X. The conditions of flask Y are 110 kPa and 320 K.

The tap is opened, meaning that ammonia starts to flow from flask Y and into flask X. The temperature decreases by 17 °C and the final pressure in both flasks is 65.0 kPa.

What is the total volume of flask X and Y in m³?

A block of solid iodine is put into a closed container at 100 kPa and left until completely sublimed to produce 1.3 dm³ of iodine vapour. 

The empty container had a mass of 3.22 g and when iodine was added the mass increased to 9.57 g.

What is the approximate temperature of the iodine vapour?

(The gas constant R = 8.31 J K^-1 mol^-1)

Which of these substances contains the greatest number of atoms?

A 5.23 g sample of anhydrous potassium sulfate is dissolved in 250 cm³ of water in a volumetric flask.

What is the concentration in mol dm^-3 of the potassium sulfate solution?

Which volume of oxygen gas, at room temperature and pressure, is required for complete combustion of 1.25 × 10⁻³ mol of propan-1-ol?