# empirical formula the empirical formula gives the simplest whole number ratio of each type of atom...

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• Empirical FormulaThe empirical formula gives the simplest whole number ratio of each type of atom in a compounde.g. The molecular formula of butane is C4H10The empirical formula of butane is C2H5

Molecular FormulaA molecular formula shows the elements that a compound is made out of and the number of atoms of each element present in one molecule of the compound. The numbers are shown written as subscripts.

e.g.

The molecular formula of butane is C4H10

One molecule of ethane contains 4 carbon atoms and 10 hydrogen atoms.

The molecular formula of water is H2O

One molecule of water contains 2 hydrogen atoms and one oxygen atom.

• ElementSymbolRelative Atomic MassHydrogen H1Carbon C12Oxygen O16Nitrogen N14Calcium Ca40Silicon Si28Relative molecular massMolecules are incredibly light so when discussing how heavy a molecule is Chemists often find the relative molecular mass. This is measured in atomic mass units. The table below shows the relative atomic masses of various elements which can be used to calculate the relative molecular mass of molecules.e.g.

The molecular formula of butane is C4H10

The relative molecular mass of ethane is 4 x 12 + 10 x 1 = 58 atomic mass units

• Elemental AnalysisIs a technique that allows a chemist to workout (as a percentage) how much each element contributes to the total mass of the molecule. If you know these percentages you can work out what the empirical formula of a molecule so it can help Chemists work out what they have made.RatioPercentagesFractionsSubstitution

• ElementSymbol Relative Atomic MassHydrogen H 1Carbon C 12Oxygen O 16Nitrogen N 14Calcium Ca 40Silicon Si 28Use your skills with fractions, percentages, ratios and substitution to work out missing information about molecules and even identify mystery compounds.

• MolecularFormulaRatioEmpirical formulaSimplified RatioRatio of massesFraction of total mass for each element% by massRelative molecular mass(amu)C3H63:6CH21:212:2C: 85.7%H: 14.3%42C12H18

C6H12O6

C6H6

CaCO3

SiH4

• There a few different ways of using this resource:Fill in the gaps in the table (possibly in pairs- each use a different colour) Cut up the completed grid and use it as a card sort (possibly only use one slide rather than two)Print the reversed complete grid with a picture on the back of the page before you cut it out into cards. Put the cards in the correct places on the template grid. Flip over each card to reveal the picture (and hence check the cards are in the correct place.

• Fill in gaps (given formula)

• MolecularFormulaRatioEmpirical formulaSimplified RatioRatio of massesFraction of total mass for each element% by massRelative molecular mass(amu)C3H6

C12H18

C6H12O6

C6H6

CaCO3

SiH4

• MolecularFormulaRatioEmpirical formulaSimplified RatioRatio of massesFraction of total mass for each element% by massRelative molecular mass(amu)CH4N60CH416CH3O62CH330C5H4128CHO290

• MolecularFormulaRatioEmpirical formulaSimplified RatioRatio of massesFraction of total mass for each element% by massRelative molecular mass(amu)C3H63:6CH21:212:2C: 85.7%H: 14.3%42C12H1812:18C2H32:324:3C: 88.9%H: 11.1%162C6H12O66:12:6CH2O1:2:112:2:16C:40%H 6.7%O: 53.3%180C6H66:6CH1:112:1C: 92.3%H: 7.7%78CaCO31:1:3CaCO31:1:340:12:48Ca: 40%C: 12%O: 48%100SiH41:4SiH41:428:4Si: 87.5%H: 12.5%32

• MolecularFormulaRatioEmpirical formulaSimplified RatioRatio of massesFraction of total mass for each element% by massRelative molecular mass(amu)C2H8N22:6:2CH4N1:4:112:4:14C:40%H: 13.3%N: 46.7%60CH41:4CH41:412:4C: 75%H: 25%16C2H6O22:6:2CH3O1:3:112:3:16C: 38.7%H: 9.7%O: 51.6%62C2H62:6CH31:312:3C: 80%H: 20%30C10H810:8C5H45:460:4C: 93.75%H: 6.25%128C2H2O42:2:4CHO21:1:212:1:32C: 26.7%H: 2.2%O: 71.1%90

• Fill in gaps (harder)

• MolecularFormulaRatioEmpirical formulaSimplified RatioRatio of massesFraction of total mass for each element% by massRelative molecular mass(amu)C3H6

C12H18

CH2O180

C:H78

Ca: 40%C: 12%O: 48%100SiH432

• MolecularFormulaRatioEmpirical formulaSimplified RatioRatio of massesFraction of total mass for each element% by massRelative molecular mass(amu)C:H:N60C: 75%H: 25%16C:H:O12:3:1662C: 80%H: 20%30C: 93.75%H: 6.25%128C: 26.7%H: 2.2%O: 71.1%90

• MolecularFormulaRatioEmpirical formulaSimplified RatioRatio of massesFraction of total mass for each element% by massRelative molecular mass(amu)C3H63:6CH21:212:26:1C: 85.7%H: 14.3%42C12H1812:18C2H32:324:38:1C: 88.9%H: 11.1%162C6H12O66:12:6CH2O1:2:112:2:166:1:8C:40%H 6.7%O: 53.3%180C6H66:6CH1:112:1C: 92.3%H: 7.7%78CaCO31:1:3CaCO31:1:340:12:4810:3:12Ca: 40%C: 12%O: 48%100SiH41:4SiH41:428:47:1Si: 87.5%H: 12.5%32

• MolecularFormulaRatioEmpirical formulaSimplified RatioRatio of massesFraction of total mass for each element% by massRelative molecular mass(amu)C2H8N22:6:2CH4N1:4:112:4:146:2:7C:40%H: 13.3%N: 46.7%60CH41:4CH41:412:43:1C: 75%H: 25%16C2H6O22:6:2CH3O1:3:112:3:16C: 38.7%H: 9.7%O: 51.6%62C2H62:6CH31:312:34:1C: 80%H: 20%30C10H810:8C5H45:460:415:1C: 93.75%H: 6.25%128C2H2O42:2:4CHO21:1:212:1:32C: 26.7%H: 2.2%O: 71.1%90

• Card sort

• MolecularFormulaRatioEmpirical formulaSimplified RatioRatio of massesFraction of total mass for each element% by massRelative molecular mass(amu)C3H63:6CH21:212:26:1C: 85.7%H: 14.3%42C12H1812:18C2H32:324:38:1C: 88.9%H: 11.1%162C6H12O66:12:6CH2O1:2:112:2:166:1:8C:40%H 6.7%O: 53.3%180C6H66:6CH1:112:1C: 92.3%H: 7.7%78CaCO31:1:3CaCO31:1:340:12:4810:3:12Ca: 40%C: 12%O: 48%100SiH41:4SiH41:428:47:1Si: 87.5%H: 12.5%32

• MolecularFormulaRatioEmpirical formulaSimplified RatioRatio of massesFraction of total mass for each element% by massRelative molecular mass(amu)C2H8N22:6:2CH4N1:4:112:4:146:2:7C:40%H: 13.3%N: 46.7%60CH41:4CH41:412:43:1C: 75%H: 25%16C2H6O22:6:2CH3O1:3:112:3:16C: 38.7%H: 9.7%O: 51.6%62C2H62:6CH31:312:34:1C: 80%H: 20%30C10H810:8C5H45:460:415:1C: 93.75%H: 6.25%128C2H2O42:2:4CHO21:1:212:1:32C: 26.7%H: 2.2%O: 71.1%90

• Card sort with template (given formula)

• MolecularFormulaRatioEmpirical formulaSimplified RatioRatio of massesFraction of total mass for each element% by massRelative molecular mass(amu)C3H6

C12H18

C6H12O6

C6H6

CaCO3

SiH4

• MolecularFormulaRatioEmpirical formulaSimplified RatioRatio of massesFraction of total mass for each element% by massRelative molecular mass(amu)C2H8N2

CH4C2H6O2

C2H6

C10H8

C2H2O4

• Relative molecular mass(amu)% by massFraction of total mass for each elementRatio of massesSimplified RatioEmpirical formulaRatioMolecularFormula42C: 85.7%H: 14.3%12:26:11:2CH23:6C3H6

162C: 88.9%H: 11.1%24:38:12:3C2H312:18C12H18

180C:40%H 6.7%O: 53.3%12:2:166:1:81:2:1CH2O6:12:6C6H12O6

78C: 92.3%H: 7.7%12:11:1CH6:6C6H6

100Ca: 40%C: 12%O: 48%40:12:4810:3:121:1:3CaCO31:1:3CaCO3

32Si: 87.5%H: 12.5%28:47:11:4SiH41:4SiH4

• (insert picture of your own choice)

• Relative molecular mass(amu)% by massFraction of total mass for each elementRatio of massesSimplified RatioEmpirical formulaRatioMolecularFormula60C:40%H: 13.3%N: 46.7%12:4:146:2:71:4:1CH4N2:6:2C2H8N2

16C: 75%H: 25%12:43:11:4CH41:4CH462C: 38.7%H: 9.7%O: 51.6%12:3:161:3:1CH3O2:6:2C2H6O2

30C: 80%H: 20%12:34:11:3CH32:6C2H6

128C: 93.75%H: 6.25%60:415:15:4C5H410:8C10H8

90C: 26.7%H: 2.2%O: 71.1%12:1:321:1:2CHO22:2:4C2H2O4

• (insert picture of your own choice)

• Card sort with template (harder)

• MolecularFormulaRatioEmpirical formulaSimplified RatioRatio of massesFraction of total mass for each element% by massRelative molecular mass(amu)C3H6

C12H18

CH2O180

C:H78

Ca: 40%C: 12%O: 48%100SiH432

• MolecularFormulaRatioEmpirical formulaSimplified RatioRatio of massesFraction of total mass for each element% by massRelative molecular mass(amu)C:H:N60C: 75%H: 25%16C:H:O12:3:1662C: 80%H: 20%30C: 93.75%H: 6.25%128C: 26.7%H: 2.2%O: 71.1%90

• MolecularFormulaRatioEmpirical formulaSimplified RatioRatio of massesFraction of total mass for each element% by massRelative molecular mass(amu)C3H63:6CH21:212:26:1C: 85.7%H: 14.3%42C12H1812:18C2H32:324:38:1C: 88.9%H: 11.1%162C6H12O66:12:6CH2O1:2:112:2:166:1:8C:40%H 6.7%O: 53.3%180C6H66:6CH1:112:1C: 92.3%H: 7.7%78CaCO31:1:3CaCO31:1:340:12:4810:3:12Ca: 40%C: 12%O: 48%100SiH41:4SiH41:428:47:1Si: 87.5%H: 12.5%32

• MolecularFormulaRatioEmpirical formulaSimplified RatioRatio of massesFraction of total mass for each element% by massRelative molecular mass(amu)C2H8N22:6:2CH4N1:4:112:4:146:2:7C:40%H: 13.3%N: 46.7%60CH41:4CH41:412:43:1C: 75%H: 25%16C2H6O22:6:2CH3O1:3:112:3:16C: 38.7%H: 9.7%O: 51.6%62C2H62:6CH31:312:34:1C: 80%H: 20%30C10H810:8C5H45:460:415:1C: 93.75%H: 6.25%128C2H2O42:2:4CHO21:1:212:1:32C: 26.7%H: 2.2%O: 71.1%90

• Relative molecular mass(amu)% by massFraction of total mass for each elementRatio of massesSimplified RatioEmpirical formulaRatioMolecularFormula42C: 85.7%H: 14.3%12:26:11:2CH23:6C3H6

162C: 88.9%H: 11.1%24:38:12:3C2H312:18C12H18

180C:40%H 6.7%O: 53.3%12:2:166:1:81:2:1CH2O6:12:6C6H12O6

78C: 92.3%H: 7.7%12:11:1CH6:6C6H6

100Ca: 40%C: 12%O: 48%40:12:4810:3:121:1:3CaCO31:1:3CaCO3

32Si: 87.5%H: 12.5%28:47:11:4SiH41:4SiH4

• (insert picture of your own choice)

• Relative molecular mass(amu)% by massFraction of total mass for each elementRatio of massesSimplified RatioEmpirical formulaRatioMolecularFormula60C:40%H: 13.3%N: 46.7%12:4:146:2:71:4:1CH4N2:6:2C2H8N2