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CALCULATIONS INVOLVING FORMULAE A guide for GCSE students

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The relative formula mass is the sum of the relativeatomic masses of ALL the atoms present in the formula

The relative formula mass is the sum of the relativeatomic masses of ALL the atoms present in the formula

To calculate this value, it is important that one understands how to work out the number of each type of atom present.

The relative formula mass is the sum of the relative atomic masses of ALL the atoms present in the formula

The relative formula mass is the sum of the relative atomic masses of ALL the atoms present in the formula

The relative formula mass is the sum of the relative atomic masses of ALL the atoms present in the formula

The relative formula mass is the sum of the relative atomic masses of ALL the atoms present in the formula

The relative formula mass is the sum of the relative atomic masses of ALL the atoms present in the formula

The relative formula mass is the sum of the relative atomic masses of ALL the atoms present in the formula

The relative formula mass is the sum of the relative atomic masses of ALL the atoms present in the formula

The relative formula mass is the sum of the relative atomic masses of ALL the atoms present in the formula

The relative formula mass is the sum of the relative atomic masses of ALL the atoms present in the formula

The relative formula mass is the sum of the relative atomic masses of ALL the atoms present in the formula

The relative formula mass is the sum of the relative atomic masses of ALL the atoms present in the formula

The masses of all the atoms at the end of a reaction (THE PRODUCTS) must equal the masses of all the atoms at the start of the reaction (THE REACTANTS).

The masses of all the atoms at the end of a reaction (THE PRODUCTS) must equal the masses of all the atoms at the start of the reaction (THE REACTANTS).

The masses of all the atoms at the end of a reaction (THE PRODUCTS) must equal the masses of all the atoms at the start of the reaction (THE REACTANTS).

CALCULATIONS INVOLVING FORMULAE

INTRODUCTION

This Powerpoint show is one of several produced to help students understand selected GCSE Chemistry topics. It is based on the requirements of the AQA specification but is suitable for other examination boards.

Individual students may use the material at home for revision purposes and it can also prove useful for classroom teaching with an interactive white board.

Accompanying notes on this, and the full range of AS and A2 Chemistry topics, are available from the KNOCKHARDY WEBSITE at...

www.knockhardy.org.uk

All diagrams, photographs and any animations in this Powerpoint are original and created by Jonathan Hopton. Permission must be obtained for their use in any work that is distributed for financial gain.

CALCULATIONS INVOLVING FORMULAE

- CONTENTS
- Working out simple formulae
- Relative formula mass
- Percentage composition
- Reacting masses
- Yield and percentage yield

SOME COMMON FORMULAE

chlorine gas Cl2

hydrogen gas H2

nitrogen gas N2

oxygen gas O2

hydrochloric acid HCl

nitric acid HNO3

sulphuric acid H2SO4

sodium hydroxide NaOH

sodium chloride NaCl

sodium carbonate Na2CO3

potassium chloride KCl

magnesium oxide MgO

magnesium hydroxide Mg(OH)2

magnesium carbonate MgCO3

magnesium sulphate MgSO4

calcium carbonate CaCO3

calcium chloride CaCl2

Many formulae can be worked out by reference to a table of ions.

Others just have to be known off by heart.

TABLE OF IONS

hydrogen H+ chloride Cl¯

sodium Na+ bromide Br¯

potassium K+ iodide I¯

lithium Li+ hydroxide OH¯

rubidium Rb+ nitrate NO3¯

caesium Cs+ nitrite NO2¯

silver(I) Ag+ hydrogencarbonate HCO3¯

ammonium NH4+ hydrogensulphate HSO4¯

calcium Ca2+ sulphate SO42-

barium Ba2+ sulphite SO32-

magnesium Mg2+ sulphide S2-

zinc Zn2+ oxide O2-

iron(II) “ferrous” Fe2+ carbonate CO32-

copper(II) Cu2+

aluminium Al3+

iron(III) “ferric” Fe3+

NUMBER OF ELECTRONS IN OUTER SHELL OF ATOMS

1 2 3 6 7

HOPTON

TABLE OF IONS

hydrogen H+ chloride Cl¯

sodium Na+ bromide Br¯

potassium K+ iodide I¯

lithium Li+ hydroxide OH¯

rubidium Rb+ nitrate NO3¯

caesium Cs+ nitrite NO2¯

silver(I) Ag+ hydrogencarbonate HCO3¯

ammonium NH4+ hydrogensulphate HSO4¯

calcium Ca2+ sulphate SO42-

barium Ba2+ sulphite SO32-

magnesium Mg2+ sulphide S2-

zinc Zn2+ oxide O2-

iron(II) “ferrous” Fe2+ carbonate CO32-

copper(II) Cu2+

aluminium Al3+

iron(III) “ferric” Fe3+

TABLE OF IONS

hydrogen H+ chloride Cl¯

sodium Na+ bromide Br¯

potassium K+ iodide I¯

lithium Li+ hydroxide OH¯

rubidium Rb+ nitrate NO3¯

caesium Cs+ nitrite NO2¯

silver(I) Ag+ hydrogencarbonate HCO3¯

ammonium NH4+ hydrogensulphate HSO4¯

calcium Ca2+ sulphate SO42-

barium Ba2+ sulphite SO32-

magnesium Mg2+ sulphide S2-

zinc Zn2+ oxide O2-

iron(II) “ferrous” Fe2+ carbonate CO32-

copper(II) Cu2+

aluminium Al3+

iron(III) “ferric” Fe3+

Formulae can be worked out by balancing the charges so that… negative charge = positive charge

CONSTRUCTING FORMULAE

CONSTRUCTING FORMULAE

Many formulae can be worked out by balancing the charges so that…

negative charge = positive charge

CONSTRUCTING FORMULAE

Q.1 Write out the correct formula for each of the following compounds.

a) sodium chloride

b) magnesium sulphate

c) potassium oxide

d) calcium chloride

e) copper(II) nitrate

sodium ionNa+

chloride ionCl¯

Cl¯

HOPTON

CONSTRUCTING FORMULAE

Q.1 Write out the correct formula for each of the following compounds.

a) sodium chloride

b) magnesium sulphate

c) potassium oxide

d) calcium chloride

e) copper(II) nitrate

sodium ionNa+

chloride ionCl¯

Cl¯

HOPTON

CONSTRUCTING FORMULAE

Q.1 Write out the correct formula for each of the following compounds.

a) sodium chloride

b) magnesium sulphate

c) potassium oxide

d) calcium chloride

e) copper(II) nitrate

sodium ionNa+

chloride ionCl¯

ONE Na+balances ONE Cl¯

FORMULA is NaCl

CONSTRUCTING FORMULAE

Q.2 Write out the correct formula for each of the following compounds.

a) sodium chloride NaCl

b) magnesium sulphate

c) potassium oxide

d) calcium chloride

e) copper(II) nitrate

magnesium ionMg2+

sulphate ionSO42-

Mg2+

SO42-

CONSTRUCTING FORMULAE

Q.2 Write out the correct formula for each of the following compounds.

a) sodium chloride NaCl

b) magnesium sulphate

c) potassium oxide

d) calcium chloride

e) copper(II) nitrate

magnesium ionMg2+

sulphate ionSO42-

Mg2+

SO42-

ONE Mg2+ balances ONE SO42-

FORMULA is MgSO4

CONSTRUCTING FORMULAE

Q.3 Write out the correct formula for each of the following compounds.

a) sodium chloride NaCl

b) magnesium sulphate MgSO4

c) potassium oxide

d) calcium chloride

e) copper(II) nitrate

K+

potassium ionK+

oxide ionO2-

K+

O2-

CONSTRUCTING FORMULAE

Q.3 Write out the correct formula for each of the following compounds.

a) sodium chloride NaCl

b) magnesium sulphate MgSO4

c) potassium oxide

d) calcium chloride

e) copper(II) nitrate

K+

potassium ionK+

oxide ionO2-

K+

O2-

TWO K+ balance ONE O2-

FORMULA is K2O

CONSTRUCTING FORMULAE

Q.4 Write out the correct formula for each of the following compounds.

a) sodium chloride NaCl

b) magnesium sulphate MgSO4

c) potassium oxide K2O

d) calcium chloride

e) copper(II) nitrate

Cl¯

calcium ionCa2+

chloride ionCl¯

Ca2+

Cl¯

CONSTRUCTING FORMULAE

Q.4 Write out the correct formula for each of the following compounds.

a) sodium chloride NaCl

b) magnesium sulphate MgSO4

c) potassium oxide K2O

d) calcium chloride

e) copper(II) nitrate

Cl¯

calcium ionCa2+

chloride ionCl¯

Ca2+

Cl¯

ONE Ca2+ balances TWOCl¯

FORMULA is CaCl2

CONSTRUCTING FORMULAE

Q.5 Write out the correct formula for each of the following compounds.

a) sodium chloride NaCl

b) magnesium sulphate MgSO4

c) potassium oxide K2O

d) calcium chloride CaCl2

e) copper(II) nitrate

NO3¯

copper(II) ionCu2+

nitrate ionNO3¯

Cu2+

NO3¯

CONSTRUCTING FORMULAE

Q.5 Write out the correct formula for each of the following compounds.

a) sodium chloride NaCl

b) magnesium sulphate MgSO4

c) potassium oxide K2O

d) calcium chloride CaCl2

e) copper(II) nitrate

NO3¯

copper(II) ionCu2+

nitrate ionNO3¯

Cu2+

NO3¯

ONE Cu2+ balances TWONO3¯

FORMULA is Cu(NO3)2

CONSTRUCTING FORMULAE

Q.5 Write out the correct formula for each of the following compounds.

a) sodium chloride NaCl

b) magnesium sulphate MgSO4

c) potassium oxide K2O

d) calcium chloride CaCl2

e) copper(II) nitrate

NO3¯

copper(II) ionCu2+

nitrate ionNO3¯

Cu2+

NO3¯

NOTE THE BRACKETS

If the brackets weren’t there, the formula would appear as CuNO32 (thirty two oxygens). Brackets are used when the ion has more than one element in it.

eg NO3¯ OH¯ NH4+

ONE Cu2+ balances TWONO3¯

FORMULA is Cu(NO3)2

FORMULAE – Test questions

Write out the correct formula for each of the following compounds.

a) lithium chlorideLiCl

b) calcium sulphateCaSO4

c) sodium oxideNa2O

d) calcium chlorideCaCl2

e) iron(II) nitrateFe(NO3)2

f) potassium sulphateK2SO4

g) calcium hydroxideCa(OH)2

h) zinc carbonateZnCO3

i) aluminium oxideAl2O3

j) aluminium sulphateAl2(SO4)3

k) ammonium nitrateNH4NO3

l) ammonium chlorideNH4Cl

m) ammonium sulphate(NH4)2SO4

n) iron(III) chloride FeCl3

FORMULAE – Test questions

Write out the correct formula for each of the following compounds.

a) lithium chlorideLiCl

b) calcium sulphateCaSO4

c) sodium oxideNa2O

d) calcium chlorideCaCl2

e) iron(II) nitrateFe(NO3)2

f) potassium sulphateK2SO4

g) calcium hydroxideCa(OH)2

h) zinc carbonateZnCO3

i) aluminium oxideAl2O3

j) aluminium sulphateAl2(SO4)3

k) ammonium nitrateNH4NO3

l) ammonium chlorideNH4Cl

m) ammonium sulphate(NH4)2SO4

n) iron(III) chloride FeCl3

RELATIVE FORMULA MASS

RELATIVE FORMULA MASS

The relative formula mass is the sum of the relativeatomic masses of ALL the atoms present in the formula

RELATIVE FORMULA MASS

The relative formula mass is the sum of the relativeatomic masses of ALL the atoms present in the formula

To calculate this value, it is important that one understands how to work out the number of each type of atom present.

RELATIVE FORMULA MASS

The relative formula mass is the sum of the relativeatomic masses of ALL the atoms present in the formula

To calculate this value, it is important that one understands how to work out the number of each type of atom present.

A small subscript number tells you how many there of the atom just before the subscript

RELATIVE FORMULA MASS

To calculate this value, it is important that one understands how to work out the number of each type of atom present.

A small subscript number tells you how many there of the atom just before the subscript

H2O2 hydrogen atoms

1 oxygen atom (a 1 after the O is unnecessary)

RELATIVE FORMULA MASS

A small subscript number tells you how many there of the atom just before the subscript

H2O 2 hydrogen atoms

1 oxygen atom (a 1 after the O is unnecessary)

Ca(OH)21 calcium atom

2 lots of everything in the bracket

ie 2 oxygen atoms and 2 hydrogen atoms

(groups of atoms occurring in brackets include… SO4 NO3 NH4 OH)

RELATIVE FORMULA MASS

HOW MANY ATOMS OF EACH TYPE ARE IN THE FOLLOWING?

a) H2O 2 x H 1 x O

b) NaOH 1 x Na 1 x O 1 x H

c) (NH4)2SO4 2 x N 4 x O 8 x H 1 x S

d) Ca(OH)2 1 x Ca 2 x O 2 x H

e) H2SO4 2 x H 4 x O 1 x S

f) CuSO4.5H2O 1 x Cu 10 x H 9 x O 1 x S

RELATIVE FORMULA MASS

HOW MANY ATOMS OF EACH TYPE ARE IN THE FOLLOWING?

a) H2O 2 x H 1 x O

b) NaOH 1 x Na 1 x O 1 x H

c) (NH4)2SO4 2 x N 4 x O 8 x H 1 x S

d) Ca(OH)2 1 x Ca 2 x O 2 x H

e) H2SO4 2 x H 4 x O 1 x S

f) CuSO4.5H2O 1 x Cu 10 x H 9 x O 1 x S

RELATIVE FORMULA MASS

HOW MANY ATOMS OF EACH TYPE ARE IN THE FOLLOWING?

a) H2O 2 x H 1 x O

b) NaOH 1 x Na 1 x O 1 x H

c) (NH4)2SO4 2 x N 4 x O 8 x H 1 x S

d) Ca(OH)2 1 x Ca 2 x O 2 x H

e) H2SO4 2 x H 4 x O 1 x S

f) CuSO4.5H2O 1 x Cu 10 x H 9 x O 1 x S

A NUMBER IN THE FRONT OF A FORMULA

MULTIPLIES EVERYTHING IN THAT FORMULA

RELATIVE FORMULA MASS

HOW MANY ATOMS OF EACH TYPE ARE IN THE FOLLOWING?

a) H2O 2 x H 1 x O

b) NaOH 1 x Na 1 x O 1 x H

c) (NH4)2SO4 2 x N 4 x O 8 x H 1 x S

d) Ca(OH)2 1 x Ca 2 x O 2 x H

e) H2SO4 2 x H 4 x O 1 x S

f) CuSO4.5H2O 1 x Cu 10 x H 9 x O 1 x S

A NUMBER IN THE FRONT OF A FORMULA

MULTIPLIES EVERYTHING IN THAT FORMULA

g) 2 NaOH 2 x Na 2 x O 2 x H

h) 3 Ca(OH)2 3 x Ca 6 x O 6 x H

i) 2 Na2HPO4 4 x Na 8 x O 2 x H 2 x P

RELATIVE FORMULA MASS

HOW MANY ATOMS OF EACH TYPE ARE IN THE FOLLOWING?

a) H2O 2 x H 1 x O

b) NaOH 1 x Na 1 x O 1 x H

c) (NH4)2SO4 2 x N 4 x O 8 x H 1 x S

d) Ca(OH)2 1 x Ca 2 x O 2 x H

e) H2SO4 2 x H 4 x O 1 x S

f) CuSO4.5H2O 1 x Cu 10 x H 9 x O 1 x S

A NUMBER IN THE FRONT OF A FORMULA

MULTIPLIES EVERYTHING IN THAT FORMULA

g) 2 NaOH 2 x Na 2 x O 2 x H

h) 3 Ca(OH)2 3 x Ca 6 x O 6 x H

i) 2 Na2HPO4 4 x Na 8 x O 2 x H 2 x P

HOPTON

RELATIVE FORMULA MASS

The relative formula mass is the sum of the relative atomic masses of ALL the atoms present in the formula

RELATIVE FORMULA MASS

The relative formula mass is the sum of the relative atomic masses of ALL the atoms present in the formula

WaterH2O

H = 1; C = 12; N = 14; O = 16; Na = 23; Mg = 24; Al = 27;

S = 32; Cl = 35.5; K = 39; Ca = 40; Fe = 56; Cu = 64

RELATIVE FORMULA MASS

The relative formula mass is the sum of the relative atomic masses of ALL the atoms present in the formula

WaterH2OH + H + O

H = 1; C = 12; N = 14; O = 16; Na = 23; Mg = 24; Al = 27;

S = 32; Cl = 35.5; K = 39; Ca = 40; Fe = 56; Cu = 64

RELATIVE FORMULA MASS

WaterH2O H + H + O

1 + 1 + 16 = 18

H = 1; C = 12; N = 14; O = 16; Na = 23; Mg = 24; Al = 27;

S = 32; Cl = 35.5; K = 39; Ca = 40; Fe = 56; Cu = 64

RELATIVE FORMULA MASS

Water H2O H + H + O

1 + 1 + 16 = 18

CopperCuSO4

sulphate

H = 1; C = 12; N = 14; O = 16; Na = 23; Mg = 24; Al = 27;

S = 32; Cl = 35.5; K = 39; Ca = 40; Fe = 56; Cu = 64

RELATIVE FORMULA MASS

Water H2O H + H + O

1 + 1 + 16 = 18

CopperCuSO4Cu + S + 4 x O

sulphate

H = 1; C = 12; N = 14; O = 16; Na = 23; Mg = 24; Al = 27;

S = 32; Cl = 35.5; K = 39; Ca = 40; Fe = 56; Cu = 64

RELATIVE FORMULA MASS

Water H2O H + H + O

1 + 1 + 16 = 18

CopperCuSO4Cu + S + 4 x O

sulphate64 + 32 + 4 x 16

H = 1; C = 12; N = 14; O = 16; Na = 23; Mg = 24; Al = 27;

S = 32; Cl = 35.5; K = 39; Ca = 40; Fe = 56; Cu = 64

RELATIVE FORMULA MASS

Water H2O H + H + O

1 + 1 + 16 = 18

CopperCuSO4Cu + S + 4 x O

sulphate64 + 32 + 4 x 16 =160

H = 1; C = 12; N = 14; O = 16; Na = 23; Mg = 24; Al = 27;

S = 32; Cl = 35.5; K = 39; Ca = 40; Fe = 56; Cu = 64

RELATIVE FORMULA MASS

Water H2O H + H + O

1 + 1 + 16 = 18

Copper CuSO4 Cu + S + 4 x O

sulphate 64 + 32 + 4 x 16 = 160

TAKE CARE WHEN THERE ARE BRACKETS

H = 1; C = 12; N = 14; O = 16; Na = 23; Mg = 24; Al = 27;

S = 32; Cl = 35.5; K = 39; Ca = 40; Fe = 56; Cu = 64

RELATIVE FORMULA MASS

Water H2O H + H + O

1 + 1 + 16 = 18

Copper CuSO4 Cu + S + 4 x O

sulphate 64 + 32 + 4 x 16 = 160

TAKE CARE WHEN THERE ARE BRACKETS

CalciumCa(OH)2

hydroxide

H = 1; C = 12; N = 14; O = 16; Na = 23; Mg = 24; Al = 27;

S = 32; Cl = 35.5; K = 39; Ca = 40; Fe = 56; Cu = 64

RELATIVE FORMULA MASS

Water H2O H + H + O

1 + 1 + 16 = 18

Copper CuSO4 Cu + S + 4 x O

sulphate 64 + 32 + 4 x 16 = 160

TAKE CARE WHEN THERE ARE BRACKETS

CalciumCa(OH)2Ca + 2 lots of OH

hydroxide

H = 1; C = 12; N = 14; O = 16; Na = 23; Mg = 24; Al = 27;

S = 32; Cl = 35.5; K = 39; Ca = 40; Fe = 56; Cu = 64

RELATIVE FORMULA MASS

Water H2O H + H + O

1 + 1 + 16 = 18

Copper CuSO4 Cu + S + 4 x O

sulphate 64 + 32 + 4 x 16 = 160

TAKE CARE WHEN THERE ARE BRACKETS

CalciumCa(OH)2Ca + 2 lots of OH

hydroxideCa + O + H + O + H

H = 1; C = 12; N = 14; O = 16; Na = 23; Mg = 24; Al = 27;

S = 32; Cl = 35.5; K = 39; Ca = 40; Fe = 56; Cu = 64

RELATIVE FORMULA MASS

Water H2O H + H + O

1 + 1 + 16 = 18

Copper CuSO4 Cu + S + 4 x O

sulphate 64 + 32 + 4 x 16 = 160

TAKE CARE WHEN THERE ARE BRACKETS

CalciumCa(OH)2Ca + 2 lots of OH

hydroxideCa + O + H + O + H

40 16 + 1 + 16 + 1

H = 1; C = 12; N = 14; O = 16; Na = 23; Mg = 24; Al = 27;

S = 32; Cl = 35.5; K = 39; Ca = 40; Fe = 56; Cu = 64

RELATIVE FORMULA MASS

Water H2O H + H + O

1 + 1 + 16 = 18

Copper CuSO4 Cu + S + 4 x O

sulphate 64 + 32 + 4 x 16 = 160

TAKE CARE WHEN THERE ARE BRACKETS

CalciumCa(OH)2Ca + 2 lots of OH

hydroxideCa + O + H + O + H

40 16 + 1 + 16 + 1=74

H = 1; C = 12; N = 14; O = 16; Na = 23; Mg = 24; Al = 27;

S = 32; Cl = 35.5; K = 39; Ca = 40; Fe = 56; Cu = 64

RELATIVE FORMULA MASS

Use the list of relative atomic masses to calculate the relative formula mass of the following compounds

H2 O2 H2O

NaOH CH4 C5H12

NaCl H2SO4 Na2SO4

CaCl2 CaCO3 NH4NO3

CuSO4 Al2O3 Ca(OH)2

Al2(SO4)3

H = 1; C = 12; N = 14; O = 16; Na = 23; Mg = 24; Al = 27;

S = 32; Cl = 35.5; K = 39; Ca = 40; Fe = 56; Cu = 64

RELATIVE FORMULA MASS

Use the list of relative atomic masses to calculate the relative formula mass of the following compounds

H2 O2 H2O

NaOH CH4 C5H12

NaCl H2SO4 Na2SO4

CaCl2 CaCO3 NH4NO3

CuSO4 Al2O3 Ca(OH)2

Al2(SO4)3

2 32 18

40 16 72

36.5 98 142

111 100 80

160 102 74

342

H = 1; C = 12; N = 14; O = 16; Na = 23; Mg = 24; Al = 27;

S = 32; Cl = 35.5; K = 39; Ca = 40; Fe = 56; Cu = 64

PERCENTAGE COMPOSITION

PERCENTAGE COMPOSITION

It can be quite useful to know how much of an element is present in a compound.

This is nothow many atoms there are BUT what mass is present.

This has some relevance when considering how much metal is in a particular ore.

PERCENTAGE COMPOSITION

Metal ores do not just contain a metal, there are other elements present.

eg Fe2O3, TiO2, ZnS.

PERCENTAGE COMPOSITION

Metal ores do not just contain a metal, there are other elements present.

eg Fe2O3, TiO2, ZnS.

To calculate the PERCENTAGE BY MASS of a metal in an ore;

PERCENTAGE COMPOSITION

- Metal ores do not just contain a metal, there are other elements present.
- eg Fe2O3, TiO2, ZnS.
- To calculate the PERCENTAGE BY MASS of a metal in an ore;
- 1 Calculate the formula mass (Fe2O3) 56 + 56 + 16 + 16 + 16 = 160

PERCENTAGE COMPOSITION

- Metal ores do not just contain a metal, there are other elements present.
- eg Fe2O3, TiO2, ZnS.
- To calculate the PERCENTAGE BY MASS of a metal in an ore;
- 1 Calculate the formula mass (Fe2O3) 56 + 56 + 16 + 16 + 16 = 160
- 2 Calculate how much of this is Fe 56 + 56 = 112

PERCENTAGE COMPOSITION

- Metal ores do not just contain a metal, there are other elements present.
- eg Fe2O3, TiO2, ZnS.
- To calculate the PERCENTAGE BY MASS of a metal in an ore;
- 1 Calculate the formula mass (Fe2O3) 56 + 56 + 16 + 16 + 16 = 160
- 2 Calculate how much of this is Fe 56 + 56 = 112
- 3 Calculate the fraction that is Fe 112
- 160

PERCENTAGE COMPOSITION

- Metal ores do not just contain a metal, there are other elements present.
- eg Fe2O3, TiO2, ZnS.
- To calculate the PERCENTAGE BY MASS of a metal in an ore;
- 1 Calculate the formula mass (Fe2O3) 56 + 56 + 16 + 16 + 16 = 160
- 2 Calculate how much of this is Fe 56 + 56 = 112
- 3 Calculate the fraction that is Fe 112
- 160
- 4 Calculate the percentage that is Fe 112 x 100 =
- 160

PERCENTAGE COMPOSITION

- Metal ores do not just contain a metal, there are other elements present.
- eg Fe2O3, TiO2, ZnS.
- To calculate the PERCENTAGE BY MASS of a metal in an ore;
- 1 Calculate the formula mass (Fe2O3) 56 + 56 + 16 + 16 + 16 = 160
- 2 Calculate how much of this is Fe 56 + 56 = 112
- 3 Calculate the fraction that is Fe 112
- 160
- 4 Calculate the percentage that is Fe 112 x 100 = 70.0%
- 160

PERCENTAGE COMPOSITION

- Metal ores do not just contain a metal, there are other elements present.
- eg Fe2O3, TiO2, ZnS.
- To calculate the PERCENTAGE BY MASS of a metal in an ore;
- 1 Calculate the formula mass (Fe2O3) 56 + 56 + 16 + 16 + 16 = 160
- 2 Calculate how much of this is Fe 56 + 56 = 112
- 3 Calculate the fraction that is Fe 112
- 160
- 4 Calculate the percentage that is Fe 112 x 100 = 70.0%
- 160
- Calculate the percentage of each metal in…Al2O3 TiO2 CuFeS2 ZnS NaCl

REACTING MASSES

REACTING MASSES

The masses of all the atoms at the end of a reaction (THE PRODUCTS) must equal the masses of all the atoms at the start of the reaction (THE REACTANTS).

REACTING MASSES

The masses of all the atoms at the end of a reaction (THE PRODUCTS) must equal the masses of all the atoms at the start of the reaction (THE REACTANTS).

copper + sulphuric acid copper + water

oxide sulphate

Write out a word equation.

REACTING MASSES

The masses of all the atoms at the end of a reaction (THE PRODUCTS) must equal the masses of all the atoms at the start of the reaction (THE REACTANTS).

copper + sulphuric acid copper + water

oxide sulphate

CuO + H2SO4 CuSO4 + H2O

Write out a proper equation showing the correct formulae.

REACTING MASSES

copper + sulphuric acid copper + water

oxide sulphate

CuO + H2SO4 CuSO4 + H2O

64 + 16 (1x1) + 32 + (4x16) 64 + 32 + (4x16) (2x1) + 16

Look up the atomic masses in a table and work out the

formula mass of each chemical in the equation.

REACTING MASSES

copper + sulphuric acid copper + water

oxide sulphate

CuO + H2SO4 CuSO4 + H2O

64 + 16 (1x1) + 32 + (4x16) 64 + 32 + (4x16) (2x1) + 16

80 98 160 18

Look up the atomic masses in a table and work out the

formula mass of each chemical in the equation.

REACTING MASSES

copper + sulphuric acid copper + water

oxide sulphate

CuO + H2SO4 CuSO4 + H2O

64 + 16 (1x1) + 32 + (4x16) 64 + 32 + (4x16) (2x1) + 16

80 98 160 18

178 178

This shows that the masses after the reaction

are the same as the masses before.

YIELD AND PERCENTAGE YIELD

YIELD AND PERCENTAGE YIELD

YIELD How much of a chemical you get

from a reaction.

PERCENTAGE How much of a chemical you get

YIELD COMPARED WITH how much you

should get. (assuming 100% conversion)

YIELD AND PERCENTAGE YIELD

YIELD How much of a chemical you get

from a reaction.

PERCENTAGE How much of a chemical you get

YIELD COMPARED WITH how much you

should get.

Example CuO + H2SO4 CuSO4 + H2O

80 98 160 18

YIELD AND PERCENTAGE YIELD

YIELD How much of a chemical you get

from a reaction.

PERCENTAGE How much of a chemical you get

YIELD COMPARED WITH how much you

should get.

Example CuO + H2SO4 CuSO4 + H2O

80 98 160 18

If you start with 80g of copper oxide, you can

get a maximum of 160g of copper sulphate.

YIELD AND PERCENTAGE YIELD

YIELD How much of a chemical you get

from a reaction.

PERCENTAGE How much of a chemical you get

YIELD COMPARED WITH how much you

should get.

Example CuO + H2SO4 CuSO4 + H2O

80 98 160 18

If you start with 80g of copper oxide, you can

get a maximum of 160g of copper sulphate.

- What is the maximum yield of copper sulphate if you
- start with a) 20g of copper oxide
- b) 400g of copper oxide

YIELD AND PERCENTAGE YIELD

YIELD How much of a chemical you get

from a reaction.

PERCENTAGE How much of a chemical you get

YIELD COMPARED WITH how much you

should get.

Example CuO + H2SO4 CuSO4 + H2O

80 98 160 18

If you start with 80g of copper oxide, you can

get a maximum of 160g of copper sulphate.

- What is the maximum yield of copper sulphate if you
- start with a)20g of copper oxide Ans. 40g
- b) 400g of copper oxide

YIELD AND PERCENTAGE YIELD

YIELD How much of a chemical you get

from a reaction.

PERCENTAGE How much of a chemical you get

YIELD COMPARED WITH how much you

should get.

Example CuO + H2SO4 CuSO4 + H2O

80 98 160 18

If you start with 80g of copper oxide, you can

get a maximum of 160g of copper sulphate.

- What is the maximum yield of copper sulphate if you
- start with a) 20g of copper oxide Ans. 40g
- b) 400g of copper oxide Ans. 800g

YIELD AND PERCENTAGE YIELD

YIELD How much of a chemical you get

from a reaction.

PERCENTAGE How much of a chemical you get

YIELD COMPARED WITH how much you

should get.

Example CuO + H2SO4 CuSO4 + H2O

80 98 160 18

- If you start with 80g of copper oxide and only get 120g of
- copper sulphate, what is the percentage yield?

YIELD AND PERCENTAGE YIELD

YIELD How much of a chemical you get

from a reaction.

PERCENTAGE How much of a chemical you get

YIELD COMPARED WITH how much you

should get.

Example CuO + H2SO4 CuSO4 + H2O

80 98 160 18

- If you start with 80g of copper oxide and only get 120g of
- copper sulphate, what is the percentage yield?
- 80g should give a maximum of 160g.

YIELD AND PERCENTAGE YIELD

YIELD How much of a chemical you get

from a reaction.

PERCENTAGE How much of a chemical you get

YIELD COMPARED WITH how much you

should get.

Example CuO + H2SO4 CuSO4 + H2O

80 98 160 18

- If you start with 80g of copper oxide and only get 120g of
- copper sulphate, what is the percentage yield?
- 80g should give a maximum of 160g.However only 120g
- are produced.

YIELD AND PERCENTAGE YIELD

YIELD How much of a chemical you get

from a reaction.

PERCENTAGE How much of a chemical you get

YIELD COMPARED WITH how much you

should get.

Example CuO + H2SO4 CuSO4 + H2O

80 98 160 18

- If you start with 80g of copper oxide and only get 120g of
- copper sulphate, what is the percentage yield?
- 80g should give a maximum of 160g. However only 120g
- are produced.The fraction produced is 120/160 = ¾ (0.75).

YIELD AND PERCENTAGE YIELD

YIELD How much of a chemical you get

from a reaction.

PERCENTAGE How much of a chemical you get

YIELD COMPARED WITH how much you

should get.

Example CuO + H2SO4 CuSO4 + H2O

80 98 160 18

- If you start with 80g of copper oxide and only get 120g of
- copper sulphate, what is the percentage yield?
- 80g should give a maximum of 160g. However only 120g
- are produced. The fraction produced is 120/160 = ¾ (0.75).
- Multiply by 100 to get the percentage.

YIELD AND PERCENTAGE YIELD

YIELD How much of a chemical you get

from a reaction.

PERCENTAGE How much of a chemical you get

YIELD COMPARED WITH how much you

should get.

Example CuO + H2SO4 CuSO4 + H2O

80 98 160 18

- If you start with 80g of copper oxide and only get 120g of
- copper sulphate, what is the percentage yield?
- 80g should give a maximum of 160g. However only 120g
- are produced. The fraction produced is 120/160 = ¾ (0.75).
- Multiply by 100 to get the percentage.ANS 75% yield

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