3.1.5

Relative Atomic Mass

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Relative Atomic Mass (Ar)

The relative atomic mass (Ar) is the average mass of all of the isotopes of an element. It takes into account how often each isotope is found (the isotope abundance).

Calculating relative atomic masses (A<sub>r</sub>)

Calculating relative atomic masses (Ar)

  • We can calculate relative atomic masses (Ar) using the expression shown above.
Equation explained

Equation explained

  • The Σ means 'sum of'.
  • The numerator is 'the sum of the isotope abundance times the isotope mass'.
  • The denominator is 'the sum of all the isotope abundances'.
E.g. a<sub>r</sub> of chlorine

E.g. ar of chlorine

  • Cl may exist as 2 isotopes, 35Cl and 37Cl.
  • Isotope abundances:
    • 75% 35Cl
    • 25% 37Cl
      • Ar = (0.75 x 35) + (0.25 x 37) = 35.5.
  • The existence of isotopes means that the relative atomic mass is not always a whole number.
Jump to other topics
1

States of Matter

1.1

States of Matter

1.1.1States of Matter1.1.2Simple Sphere1.1.3Changes of State1.1.4Changes of State 21.1.5Changes of State 31.1.6Changes of State and Temperature1.1.7Solubility1.1.8Solubility Curves1.1.9Solubility - Experiments1.1.10Diffusion - Experiment1.1.11Changing State HyperLearning
2

Elements, Compounds & Mixtures

2.1

Elements, Mixtures & Compounds

2.1.1Elements & Compounds2.1.2Chemical Formula2.1.3Mixtures2.1.4Purity2.1.5Separating Mixtures2.1.6Separating Mixtures 22.1.7Paper Chromatography2.1.8Paper Chromatography Analysis2.1.9Paper Chromatography - Practical2.1.10End of Topic Test - Elements,Compounds,Mixtures2.1.11Grade 9 - Chromatography2.1.12Exam-Style Questions - Separation of Mixtures
3

Atomic Structure

3.1

Atoms

3.1.1Atomic Structure3.1.2Atom Size3.1.3Subatomic Particles3.1.4Atomic Number3.1.5Relative Atomic Mass3.1.6Isotopes3.1.7Isotopes 2
4

The Periodic Table

4.1

The Periodic Table

4.1.1Periodic Table Arrangement4.1.2Electron Structure4.1.3Metals & Non-Metals4.1.4Noble Gases4.1.5End of Topic Test- Atomic Structure,Periodic Table4.1.6Grade 9 - Atomic Structure, Periodic Table4.1.7Exam-Style Questions -Alkali Metals
5

Chemical Formulae, Equations & Calculations

5.1

Equations

5.1.1Forming Equations5.1.2Balancing Symbols5.1.3State Symbols5.1.4Relative Formula Mass5.1.5Calculating Relative Formula Mass5.1.6Relative Formula Mass - Calculations5.1.7Introducing Moles5.1.8Relative Formula Mass5.1.9Amounts of Substance5.1.10Moles & Yield5.1.11Moles - Calculations5.1.12Balancing Equations5.1.13Moles to Balance Equations5.1.14Limiting Reactants5.1.15Chemical Measurements5.1.16Calculating Mass5.1.17Changing Mass5.1.18Exam-Style Questions - Moles5.1.19Percentage Yield5.1.20Calculating Yield5.1.21Percentage Yield - Calculations5.1.22Empirical & Molecular Formula5.1.23Experiment for Empirical Formula5.1.24Empirical Formula - Calculations5.1.25Concentrations & Amounts5.1.26Conclusion of Solutions5.1.27Volumes and Gases5.1.28Concentration & Amounts - Calculations5.1.29End of Topic Test - Equations5.1.30Grade 9 - Equations
6

Bonding

6.1

Ionic Bonding

6.1.1Dot & Cross Diagrams6.1.2Changes in Number of Subatomic Particles6.1.3Ionic Bonding6.1.4Ions6.1.5Types of Bonding6.1.6Ion Formation6.1.7Identifying Ionic Compounds6.1.8Ionic Compounds6.1.9Ionic and Metallic Bonding6.1.10Ion Charges
6.2

Covalent Bonding

6.2.1Covalent Bonding6.2.2Dot-and-Cross Diagrams6.2.3Representing Covalent Bonds6.2.4Covalent Bond Examples6.2.5Covalent Bond Examples 26.2.6Simple Covalent Molecules6.2.7Chemical Properties of Small Molecules6.2.8Giant Covalent Structures6.2.9Giant Covalent Structures 26.2.10Carbon Structures - Diamonds6.2.11Carbon Structures - Graphite6.2.12Carbon Structures - Fullerenes6.2.13Carbon Structures - Summary6.2.14Exam-Style Questions - Allotropes of Carbon
6.3

Metallic Bonding

6.3.1Metallic Bonding6.3.2Metals as Conductors6.3.3Pure Metals6.3.4End of Topic Test - Bonding6.3.5Grade 9 - Bonding6.3.6Exam-Style Questions - Metals
7

Electrolysis

7.1

Electrolysis

7.1.1Molten Ionic Compounds7.1.2Electrolysis - Process7.1.3Electrolysis - Aqueous Solutions7.1.4Electrolysis - Copper Sulfate7.1.5Electrolysis - Examples7.1.6Half Equations7.1.7Exam-Style Questions - Electrolysis
8

Groups of the Periodic Table

8.1

Alkali Metals & Halogens

8.1.1Alkali Metals8.1.2Alkali Metals - Properties8.1.3Alkali Metal Reactions8.1.4Reactivity of Alkali Metals8.1.5Halogens - Properties8.1.6Halogens - Colours and States8.1.7Halogen - Displacement Reactions8.1.8Halogen - Displacement Reactions 28.1.9Reactions Between Halogens and Metals8.1.10Hydrogen Halides8.1.11End of Topic Test - Alkali Metals & Halogens8.1.12Grade 9 - Alkali Metals & Halogens8.1.13Exam-Style Questions - Alkali Metals
9

The Atmosphere

9.1

Gases in the Atmosphere

9.1.1Gases in the Air9.1.2Calculating Oxygen in the Air - Metal9.1.3Calculating Oxygen in the Air - Non-Metal9.1.4Oxygen9.1.5Carbon Dioxide9.1.6Greenhouse Gases9.1.7Greenhouse Gases & Human Activities9.1.8Greenhouse Gases & Climate9.1.9End of Topic Test - Gases in the Atmosphere9.1.10Grade 9 - Gases in the Atmosphere
10

Reactivity Series

10.1

Reactivity Series

10.1.1Reactivity Diagram10.1.2Displacement Reactions10.1.3Reactivity Tests - Water10.1.4Reactivity Tests - Acid10.1.5Reactivity Tests - Metals10.1.6Corrosion10.1.7Preventing Corrosion10.1.8Metal Oxide10.1.9Oxidisation & Reduction10.1.10Redox Reactions10.1.11End of Topic Test - Reactivity Series10.1.12Grade 9 - Reactivity Series10.1.13Exam-Style Questions - Redox Reactions
11

Metal Extraction

11.1

Metal Extraction

11.1.1Extracting Metals11.1.2Extracting Metals - Electrolysis11.1.3Alloys11.1.4Metal Alloys11.1.5End of Topic Test - Extracting Metals11.1.6Grade 9 - Extracting Metals
12

Acids & Alkalis

12.1

Acids, Alkalis & Titrations

12.1.1Acids and Alkali Indicators12.1.2Is it an Acid or Alkali?12.1.3The pH Scale12.1.4Titrations12.1.5Titration - Practical12.1.6Titrations - Methods12.1.7Soluble Salts12.1.8Solubility of Salts12.1.9Making Insoluble Salts12.1.10Required Practical: Separating Mixtures12.1.11Reaction of Acid & Metals12.1.12Neutralisation of Acids12.1.13Strong vs Weak Bases12.1.14End of Topic Test - Acids & Alkalis12.1.15Grade 9 - Acids & Alkalis12.1.16Exam-Style Questions - Neutralisation & Titrations
13

Chemical Tests

13.1

Identifying Gases

13.1.1Hydrogen13.1.2Oxygen13.1.3Carbon Dioxide13.1.4Chlorine13.1.5Ammonia
13.2

Testing Anions, Cations & Water

13.2.1Flame Tests13.2.2Flame Test - Practical13.2.3Metal Hydroxides13.2.4Testing Cations13.2.5Testing for Aqueous Cations13.2.6Testing Carbonates13.2.7Testing Halides13.2.8Testing for Carbonate and Halides13.2.9Testing Sulfates13.2.10Testing Sulfates 213.2.11Testing Water13.2.12Testing Water Purity13.2.13End of Topic Test - Chemical Tests13.2.14Grade 9 - Chemical Tests13.2.15Exam-Style Questions - Identifying Gases & Ions
14

Physical Chemistry

14.1

Energetics

14.1.1Energy Conservation14.1.2Exothermic Reactions14.1.3Endothermic Reactions14.1.4Heat Changes14.1.5Calculating Heat Energy Transferred14.1.6Molar Enthalpy Change14.1.7Reaction Profiles14.1.8Reaction Profiles - Catalysed vs Uncatalysed14.1.9Exam-Style Questions - Reaction Profiles14.1.10Chemical Bonds14.1.11Bond Energies
14.2

Rates of Reaction

14.2.1Reaction Practicals - Measuring Gas Production14.2.2Reaction Practicals - Observing a Colour Change14.2.3Rate of Reaction - Collision Theory14.2.4Rate of Reaction - Key Factors14.2.5Rate of Reaction - Catalysts14.2.6End of Topic Test - Energetics & Rates14.2.7Grade 9 - Energetics & Rates
14.3

Reversible Reactions & Equilibria

14.3.1Reversible Reactions14.3.2Dynamic Equilibrium14.3.3Conditions and Equilibrium14.3.4Equilibrium Position - Temperature14.3.5Equilibrium Position - Pressure14.3.6End of Topic Test - Equilibria
15

Organic Chemistry

15.1

Hydrocarbons

15.1.1Crude Oil15.1.2Properties of Hydrocarbons15.1.3Fractional Distillation15.1.4Process of Fractional Distillation15.1.5Fractions15.1.6Combustion of Hydrocarbons15.1.7Impurities15.1.8Heavy Fractions of Crude Oil15.1.9Cracking
15.2

Alkanes & Alkenes

15.2.1Homologous Series15.2.2Alkanes15.2.3Smallest Alkanes15.2.4Structural Isomerism15.2.5Structure of Alkenes15.2.6The Shortest Alkenes15.2.7Alkene Reactions15.2.8Types of Alkene Reactions15.2.9Q5 - Alkene Reactions
15.3

Alcohols

15.3.1Alcohols15.3.2Smallest Alcohols15.3.3Combustion of Alcohols15.3.4Oxidisation of Ethanol15.3.5Fermentation15.3.6Ethanol Hydration15.3.7Fermentation vs Hydration of Ethene
15.4

Carboxylic Acids

15.4.1Carboxylic Acids15.4.2Smallest Carboxylic Acids15.4.3Reactions of Carboxylic Acids
15.5

Esters

15.5.1Esters15.5.2Ethyl Ethanoate
15.6

Synthetic Polymers

15.6.1Polymers15.6.2Addition Polymerisation15.6.3Examples of Addition Polymerisation15.6.4Problems With Polymers15.6.5Condensation Polymerisation
15.7

End of Topic - Organic Chemistry

15.7.1End of Topic Test - Organic Chemistry15.7.2Grade 9 - Organic Chemistry15.7.3Exam-Style Questions - Organic Compounds

Practice questions on Relative Atomic Mass

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  1. 1
    75% of Cl atoms have a mass number of 35, whilst the remaining 25% have a mass number of 37. What is the relative atomic mass of chlorine? Multiple choice
  2. 2
    What is the shorthand for relative atomic mass?Multiple choice
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Atomic Number

Isotopes