New
New
Year 10
OCR
Higher

Converting between mass and volume using moles (RAM 1 d.p.)

I can combine mathematical relationships to calculate an unknown mass or volume.

New
New
Year 10
OCR
Higher

Converting between mass and volume using moles (RAM 1 d.p.)

I can combine mathematical relationships to calculate an unknown mass or volume.

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Lesson details

Key learning points

  1. The volume of one mole of any gas at room temperature and pressure (20℃ and 1 atmosphere pressure) is 24 dm³.
  2. Reacting mass calculations can use a combination of mass to volume calculations and vice versa.
  3. Amount of substance (moles) can be calculated using multiple equations.
  4. The choice of equation for calculating moles depends on the context of the problem or calculation.

Keywords

  • Mole - A mole of something is 6.02 × 10²³ of it. The mass of a mole of a substance is its relative mass expressed in grams.

  • Volume - Volume is how much 3D space matter occupies. It is usually measured in cm³.

  • Molar gas volume - Molar gas volume is the volume occupied by one mole of any gas. It is equal to 24 dm³ or 24 000 cm³ at room temperature and pressure.

  • Stoichiometry - Stoichiometry refers to the molar ratio of the reactants and products in a chemical reaction.

  • Balanced symbol equation - A balanced symbol equation describes a reaction using a symbol equation with coefficients, which ensure there are equal numbers of atoms of each element on both sides of the symbol equation.

Common misconception

Pupils use an incorrect mathematical relationship to calculate the number of moles in a sample.

Depending on the type of substance (solid, solution or gas) a specific mathematical relationship for moles must be used. Challenge pupils to classify substances as (s), (aq), or (g) and apply correct mathematical relationship.

Limestone is roasted with clay to form cement, producing carbon dioxide in the process. Challenge pupils to determine the volume of carbon dioxide produced when a sample of limestone decomposes when heated.
Teacher tip

Equipment

Sample of limestone (calcium carbonate), balance, tongs, heatproof mat, Bunsen burner, tripod, gauze.

Content guidance

  • Risk assessment required - equipment

Supervision

Adult supervision required

Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

Lesson video

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6 Questions

Q1.
Which unit is most commonly used to measure the volume of a gas?
L
ml
Correct answer: cm³
dm³
Q2.
What is the molar gas volume of any gas at room temperature and pressure (20°C and 1 atmosphere)?
12 dm³
18 dm³
Correct answer: 24 dm³
36 dm³
Q3.
Molar gas volume is the volume occupied by of any gas at room temperature and pressure, standardised at 24 dm³ or 24 000 cm³.
Correct Answer: one mole, 1 mole, a mole
Q4.
Which equation would you use to calculate the number of moles from the volume of a gas?
moles = mass ÷ molar mass
Correct answer: moles = volume ÷ molar volume
moles = density × volume
moles = concentration × volume
Q5.
True or false? The number of moles of a gas can only be calculated if you know the volume of the gas and the conditions of temperature and pressure.
Correct answer: true
false
Q6.
Calculate the volume of 0.5 moles of nitrogen gas at room temperature and pressure. Assume the molar gas volume is 24 dm³ per mole. Give your answer to 2 s.f. Volume of nitrogen gas = dm³.
Correct Answer: 12, 12.0, twelve

6 Questions

Q1.
When converting the volume of a gas to the mass of a solid reactant in a balanced reaction, what must you first determine?
the density of the gas
the relative mass of the solid
Correct answer: the number of moles of gas
the temperature of the gas
Q2.
Order the following steps to calculate the mass of a solid reactant from the volume of a gas product in a chemical reaction. Starting with the volume of gas.
1 - Determine the volume of the gas.
2 - Calculate the number of moles of gas from its volume.
3 - Use the stoichiometry of the balanced equation to find the moles of reactant.
4 - Calculate the mass of the reactant using its relative mass.
Q3.
If 24 dm³ of hydrogen gas react with oxygen to form water, how many moles of oxygen gas were used? 2H₂ + O₂ → 2H₂O.
1 mole
2 moles
Correct answer: 0.5 moles
1.5 moles
Q4.
A sample of oxygen gas weighing 16 g is used in a reaction. Calculate the volume it occupies at room temperature and pressure. The RFM of oxygen (O₂) is 32.0. The molar gas volume is 24 dm³.
Correct answer: 12 dm³
24 dm³
36 dm³
384 dm³
0.67 dm³
Q5.
Calculate the volume of CO₂ gas produced when 100 g of CaCO₃ decomposes. CaCO₃ → CaO + CO₂. Assume all of the CaCO₃ reacts, the molar gas volume is 24 dm³. RFM CaCO₃ = 100.1, CaO = 56.1, CO₂ = 44.0
12 dm³
Correct answer: 24 dm³
48 dm³
43 dm³
13 dm³
Q6.
Given 500 cm³ of oxygen gas at RTP, calculate the mass of H₂ gas that completely reacts with it to form water. Give answer to 2 s.f. 2H₂ + O₂ → 2H₂O. The molar gas volume is 24 dm³. RFM of H₂ = 2.0
Correct Answer: 0.083 g, 0.083g, 0.083