Relative Masses (OCR Gateway GCSE Chemistry: Combined Science)

Revision Note

Author

Alexandra Brennan

Last updated

3 March 2022

Relative Masses

Relative atomic mass has the symbol Ar
This is the average mass of the atoms of an element measured relative to the mass of one atom of carbon-12
This is calculated from the mass number and relative abundances of all the isotopes of a particular element
Relative molecular mass is the average mass of the atoms of one molecule of an element or compound measured relative to the mass of one atom of carbon-12
Relative formula mass has the symbol Mr and it refers to the total mass of the molecule
To calculate the Mr of a substance, you have to add up the relative atomic masses of all the atoms present in the formula

Calculating Relative Formula Mass

Relative Formula Mass Calculations Table, downloadable IGCSE & GCSE Chemistry revision notes

Examiner Tip

The relative atomic mass of every element is given on the Periodic Table. It is the larger of the two numbers.

In accordance with the Law of Conservation of Mass, in a balanced chemical equation, the sum of the relative molecular masses of the reactants will be the same as the sum of the relative molecular masses of the products

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Previous:2.1.1 Pure & ImpureNext:2.1.3 Empirical Formula

Relative Masses (OCR Gateway GCSE Chemistry: Combined Science)

Revision Note

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1. Particles

1.1 The Particle Model

1.1.1 The Particle Model

1.1.2 Limitations of the Particle Model

1.2 Atomic Structure

1.2.1 Atomic Models Through Time

1.2.2 Atomic Structure

1.2.3 Calculating the Particles

2. Elements, compounds & mixtures

2.1 Purity & Separating Mixtures

2.1.1 Pure & Impure

2.1.2 Relative Masses

2.1.3 Empirical Formula

2.1.4 Alloys

2.1.5 Separation Techniques

2.1.6 Chromatography

2.2 Bonding

2.2.1 Metals & Non-Metals

2.2.2 Electronic Structure

2.2.3 Ionic Bonding

2.2.4 Covalent Bonding

2.2.5 Giant Covalent Structures

2.2.6 Polymers

2.2.7 Metals

2.2.8 Atomic Structure & the Periodic Table

2.3 Properties of Materials

2.3.1 Carbon

2.3.2 Changes of State

2.3.3 Bulk Properties

3. Chemical Reactions

3.1 Introducing Chemical Reactions

3.1.1 Chemical Symbols & Formulae

3.1.2 Deducing Formulae Using Common Ions

3.1.3 Balancing Chemical Equations

3.1.4 Writing Balanced Ionic Equations

3.1.5 The Avogadro Constant

3.1.6 Conservation of Mass

3.1.7 Using Moles to Balance Equations

3.1.8 Calculating Masses from Balanced Equations

3.2 Energetics

3.2.1 Exothermic & Endothermic Reactions

3.2.2 Calculating Energy Changes

3.3 Types of Chemical Reactions

3.3.1 Oxidation & Reduction

3.3.2 Oxidation & Reduction in Terms of Electrons

3.3.3 Acids & Alkalis

3.3.4 Neutralisation

3.3.5 Effect of Hydrogen Ion Concentration on pH

3.4 Electrolysis

3.4.1 Electrolysis

3.4.2 Electrolysis of Aqueous Solutions

3.4.3 Reactions at Electrodes

3.4.4 Half Equations

4. Predicting & Identifying Reactions & Products

4.1 Predicting Chemical Reactions

4.1.1 Group 1

4.1.2 Group 7

4.1.3 Group 0

4.1.4 The Reactivity Series

4.2 Identifying the Products of Chemical Reactions

4.2.1 Testing for Common Gases

5. Monitoring & Controlling Chemical Reactions

5.1 Monitoring Chemical Reactions

5.1.1 Measuring Rates

5.1.2 Rate Graphs

5.1.3 Change Rates

5.1.4 Catalysts & Enzymes

5.2 Controlling Reactions

5.2.1 Equilibrium

5.2.2 Le Chatelier's Principle

6.Global Challenges

6.1 Improving Processes & Products

6.1.1 Extracting Metals

6.1.2 Biological Extraction Methods

6.1.3 Life Cycle Assessment