What is one mole of a substance?

One mole is the amount of substance containing 6.02 × 10²³ particles, the Avogadro constant. A mole of a substance has a mass in grams equal to its relative formula mass.

State the relationship between amount in moles, mass and molar mass.

The amount in moles equals the mass in grams divided by the molar mass in g mol⁻¹. Mass equals moles multiplied by molar mass.

A water-treatment chemist weighs out 5.30 g of anhydrous sodium carbonate, Na₂CO₃ (Mr = 106.0). How many moles is this?

The sample contains 0.0500 mol of sodium carbonate. The working is 5.30 ÷ 106.0 = 0.0500 mol.

Why must a symbol equation be balanced before it is used to calculate reacting quantities?

A balanced equation gives the mole ratio in which substances react and form. An unbalanced equation gives the wrong ratio and so the wrong masses.

CCEA A-Level Life and Health Sciences 0008

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Physical Chemistry in Industrial Processes

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Physical Chemistry in Industrial Processes

Moles, reacting masses and percentage yield

3 things to know
AS 3

Overview

Relative formula mass, the mole, balancing equations, reacting masses in industrial processes, theoretical and percentage yield in the Haber process, and atom economy.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

What mass of calcium carbonate (Mr = 100.1) must be heated to make 14.0 tonnes of calcium oxide (Mr = 56.1)?

Key term

What is the relative formula mass of a substance?

Numbers

Calculate the relative formula mass of sulfuric acid, H₂SO₄, using Ar values H = 1.0, S = 32.1 and O = 16.0.

Questions from this subtopic

Each one with the model answer underneath.

1
What is the relative formula mass of a substance?
Model answer
The relative formula mass is the sum of the relative atomic masses of all the atoms in its formula. Relative formula mass has no units.
2
Calculate the relative formula mass of sulfuric acid, H₂SO₄, using Ar values H = 1.0, S = 32.1 and O = 16.0.
Model answer
The relative formula mass of H₂SO₄ is 98.1. The working is (2 × 1.0) + 32.1 + (4 × 16.0) = 98.1.
3
What is one mole of a substance?
Model answer
One mole is the amount of substance containing 6.02 × 10²³ particles, the Avogadro constant. A mole of a substance has a mass in grams equal to its relative formula mass.
4
State the relationship between amount in moles, mass and molar mass.
Model answer
The amount in moles equals the mass in grams divided by the molar mass in g mol⁻¹. Mass equals moles multiplied by molar mass.
5
A water-treatment chemist weighs out 5.30 g of anhydrous sodium carbonate, Na₂CO₃ (Mr = 106.0). How many moles is this?
Model answer
The sample contains 0.0500 mol of sodium carbonate. The working is 5.30 ÷ 106.0 = 0.0500 mol.
6
Why must a symbol equation be balanced before it is used to calculate reacting quantities?
Model answer
A balanced equation gives the mole ratio in which substances react and form. An unbalanced equation gives the wrong ratio and so the wrong masses.

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