Stoichiometry Chapter Notes | Chemistry for GCSE/IGCSE - Year 11 PDF Download

 Page 1


Mo l e s
? ? 1 mole is atoms/molecules  1 gram of atomic mass 6 ?? 10
23
? Relative atomic mass (AR)
? It is the average mass of one atom of the element when compared with 1/12 of the mass
of an atom of C-12
? ? RAM = 1
?? h?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ???? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ???? ?? h?? ?? ?? ?? ?? ?? ?? 1 ?? ?? ?? ?? ?? ?? ?? -12
? Relative molecular mass (MR)
? It is the average mass of one molecule of a substance when compared with 1/12 of the
mass of one atom of C-12
? RMM =
?? h?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ???? ?? ?? ?? ?? ?? ???? ?? ?? ?? ?? ?? ?? ?? ?? ???? ?? h?? ?? ?? ?? ?? ?? ?? 1 ?? ?? ?? ?? ?? ?? ?? -12
? ? ? MR of CaCl2  Ca(40) + Cl(35.5) + Cl(35.5)  111
? Calculate percentage composition
? ? Fe2O3  find percentage composition of iron in iron oxide
? ? ? MR  160, molar mass/AR of iron  112
? ? 112/160 x 100  70%
? ? Number of moles  Mass/ Molar mass(MR)
? ? ? Mass  MR x moles / MR  mass/moles
? Different kinds of molecular formula
? Shows atomic number and kinds of atoms present
Empirical formula
? Shows the simplest whole number ratio of atoms present
? ? C2H6  C1H3
? ? Mass of Mg burnt  .48g
? ? Mass of Mg produced  .8g (times 2)
? ? 2Mg + O2  2MgO
M g O
M a s s .48 .32
M r 24 16
D i vi d e .48 / 24 .02 ? .32 / 16  .02 ?
R a t i o 1 1
Page 2


Mo l e s
? ? 1 mole is atoms/molecules  1 gram of atomic mass 6 ?? 10
23
? Relative atomic mass (AR)
? It is the average mass of one atom of the element when compared with 1/12 of the mass
of an atom of C-12
? ? RAM = 1
?? h?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ???? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ???? ?? h?? ?? ?? ?? ?? ?? ?? 1 ?? ?? ?? ?? ?? ?? ?? -12
? Relative molecular mass (MR)
? It is the average mass of one molecule of a substance when compared with 1/12 of the
mass of one atom of C-12
? RMM =
?? h?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ???? ?? ?? ?? ?? ?? ???? ?? ?? ?? ?? ?? ?? ?? ?? ???? ?? h?? ?? ?? ?? ?? ?? ?? 1 ?? ?? ?? ?? ?? ?? ?? -12
? ? ? MR of CaCl2  Ca(40) + Cl(35.5) + Cl(35.5)  111
? Calculate percentage composition
? ? Fe2O3  find percentage composition of iron in iron oxide
? ? ? MR  160, molar mass/AR of iron  112
? ? 112/160 x 100  70%
? ? Number of moles  Mass/ Molar mass(MR)
? ? ? Mass  MR x moles / MR  mass/moles
? Different kinds of molecular formula
? Shows atomic number and kinds of atoms present
Empirical formula
? Shows the simplest whole number ratio of atoms present
? ? C2H6  C1H3
? ? Mass of Mg burnt  .48g
? ? Mass of Mg produced  .8g (times 2)
? ? 2Mg + O2  2MgO
M g O
M a s s .48 .32
M r 24 16
D i vi d e .48 / 24 .02 ? .32 / 16  .02 ?
R a t i o 1 1
C u O
M a s s 8 1
M r 64 16
D i vi d e 8/64  .125 ? 1/16  .0625 ?
R a t i o .125/.0635  2 ? .0625/.0625  1 ?
Cu2O
? Oxide of sulfur contains 40% S and 60% oxygen. Find EF
S O
M a s s 40 60
M r 32 16
D i vi d e 1.25 3.75
R a t i o 1 3
SO3
The structural formula
? Model of showing molecules and the bonds e.g. ethane
? ? H - O - H  H2O
The molecular formula
? EF = CH2, the RMM is 42, find molecular formula of CH2
? ? The RMM  12n + 2n = 14n
42 = 14n
n = 3
? ? CH2 x 3  C3H6
? Avogadro's number
? Equal volume of gases, at the same temperature and pressure, contain equal number of
particles
? The molar volume of a gas is the volume occupied by 1 mole of the gas
? At RTP (room temperature) which is 25 degree and 1 atm of gas has a volume of 24dm3 or
24000cm3
Page 3


Mo l e s
? ? 1 mole is atoms/molecules  1 gram of atomic mass 6 ?? 10
23
? Relative atomic mass (AR)
? It is the average mass of one atom of the element when compared with 1/12 of the mass
of an atom of C-12
? ? RAM = 1
?? h?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ???? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ???? ?? h?? ?? ?? ?? ?? ?? ?? 1 ?? ?? ?? ?? ?? ?? ?? -12
? Relative molecular mass (MR)
? It is the average mass of one molecule of a substance when compared with 1/12 of the
mass of one atom of C-12
? RMM =
?? h?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ???? ?? ?? ?? ?? ?? ???? ?? ?? ?? ?? ?? ?? ?? ?? ???? ?? h?? ?? ?? ?? ?? ?? ?? 1 ?? ?? ?? ?? ?? ?? ?? -12
? ? ? MR of CaCl2  Ca(40) + Cl(35.5) + Cl(35.5)  111
? Calculate percentage composition
? ? Fe2O3  find percentage composition of iron in iron oxide
? ? ? MR  160, molar mass/AR of iron  112
? ? 112/160 x 100  70%
? ? Number of moles  Mass/ Molar mass(MR)
? ? ? Mass  MR x moles / MR  mass/moles
? Different kinds of molecular formula
? Shows atomic number and kinds of atoms present
Empirical formula
? Shows the simplest whole number ratio of atoms present
? ? C2H6  C1H3
? ? Mass of Mg burnt  .48g
? ? Mass of Mg produced  .8g (times 2)
? ? 2Mg + O2  2MgO
M g O
M a s s .48 .32
M r 24 16
D i vi d e .48 / 24 .02 ? .32 / 16  .02 ?
R a t i o 1 1
C u O
M a s s 8 1
M r 64 16
D i vi d e 8/64  .125 ? 1/16  .0625 ?
R a t i o .125/.0635  2 ? .0625/.0625  1 ?
Cu2O
? Oxide of sulfur contains 40% S and 60% oxygen. Find EF
S O
M a s s 40 60
M r 32 16
D i vi d e 1.25 3.75
R a t i o 1 3
SO3
The structural formula
? Model of showing molecules and the bonds e.g. ethane
? ? H - O - H  H2O
The molecular formula
? EF = CH2, the RMM is 42, find molecular formula of CH2
? ? The RMM  12n + 2n = 14n
42 = 14n
n = 3
? ? CH2 x 3  C3H6
? Avogadro's number
? Equal volume of gases, at the same temperature and pressure, contain equal number of
particles
? The molar volume of a gas is the volume occupied by 1 mole of the gas
? At RTP (room temperature) which is 25 degree and 1 atm of gas has a volume of 24dm3 or
24000cm3
? Number of moles = Volume of gas/ RTP (24)
? Volume of gas = 24 x number of moles
? Concentration
? A concentration of 1 mole per dm3 is written as 1 mole/dm3
? Concentration = mass/volume of (gas/solute)
? Concentration = moles/volume of (gas/solute)
? Moles = concentration x volume
? Limiting reactant
? It is the reactant that is not in excess
? ? 2SO2 + O2  NA2CO3
2 moles 1.75 moles
? Oxygen is not in excess which makes it the limiting reactant