Moles
โ— 1 mole is atoms/molecules โ†’ 1 gram of atomic mass
6 ๐‘ฅ 10
23
โ— Relative atomic mass (AR)
โ—‹ 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
โ—‹ RAM = โ†’ 1
๐‘กโ„Ž๐‘’ ๐‘Ž๐‘ฃ๐‘’๐‘Ÿ๐‘Ž๐‘”๐‘’ ๐‘š๐‘Ž๐‘ ๐‘  ๐‘œ๐‘“ ๐‘œ๐‘›๐‘’ ๐‘Ž๐‘ก๐‘œ๐‘š ๐‘œ๐‘“ ๐‘’๐‘™๐‘’๐‘š๐‘’๐‘›๐‘ก
๐‘กโ„Ž๐‘’ ๐‘š๐‘Ž๐‘ ๐‘  ๐‘œ๐‘“ 1 ๐‘Ž๐‘ก๐‘œ๐‘š ๐‘œ๐‘“ ๐‘โˆ’12
โ— Relative molecular mass (MR)
โ—‹ 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
โ—‹ RMM =
๐‘กโ„Ž๐‘’ ๐‘Ž๐‘ฃ๐‘’๐‘Ÿ๐‘Ž๐‘”๐‘’ ๐‘š๐‘Ž๐‘ ๐‘  ๐‘œ๐‘“ ๐‘œ๐‘›๐‘’ ๐‘š๐‘œ๐‘™๐‘’๐‘๐‘ข๐‘™๐‘’ ๐‘œ๐‘“ ๐‘’๐‘™๐‘’๐‘š๐‘’๐‘›๐‘ก
๐‘กโ„Ž๐‘’ ๐‘š๐‘Ž๐‘ ๐‘  ๐‘œ๐‘“ 1 ๐‘Ž๐‘ก๐‘œ๐‘š ๐‘œ๐‘“ ๐‘โˆ’12
โ—‹ MR of CaCl2 โ†’ Ca(40) + Cl(35.5) + Cl(35.5) โ†’ 111
โ— Calculate percentage composition
โ—‹ Fe2O3 โ†’ find percentage composition of iron in iron oxide
โ—‹ MR โ†’ 160, molar mass/AR of iron โ†’ 112
โ—‹ 112/160 x 100 โ†’ 70%
โ— Number of moles โ†’ Mass/ Molar mass(MR)
โ— Mass โ†’ MR x moles / MR โ†’ mass/moles
โ— Different kinds of molecular formula
โ—‹ Shows atomic number and kinds of atoms present
Empirical formula
โ— Shows the simplest whole number ratio of atoms present
โ—‹ C2H6 โ†’ C1H3
โ— Mass of Mg burnt โ†’ .48g
โ— Mass of Mg produced โ†’ .8g (times 2)
โ— 2Mg + O2 โ†’ 2MgO
Mg
O
Mass
.48
.32
Mr
24
16
Divide
.48 / 24โ†’ .02
.32 / 16 โ†’ .02
Ratio
1
1
Cu
O
Mass
8
1
Mr
64
16
Divide
8/64 โ†’ .125
1/16 โ†’ .0625
Ratio
.125/.0635 โ†’ 2
.0625/.0625 โ†’ 1
Cu2O
โ— Oxide of sulfur contains 40% S and 60% oxygen. Find EF
S
O
Mass
40
60
Mr
32
16
Divide
1.25
3.75
Ratio
1
3
SO3
The structural formula
โ— Model of showing molecules and the bonds e.g. ethane
โ— H - O - H โ†’ H2O
The molecular formula
โ— EF = CH2, the RMM is 42, find molecular formula of CH2
โ— The RMM โ†’ 12n + 2n = 14n
42 = 14n
n = 3
โ— CH2 x 3 โ†’ C3H6
โ— Avogadro's number
โ—‹ Equal volume of gases, at the same temperature and pressure, contain equal number of
particles
โ— The molar volume of a gas is the volume occupied by 1 mole of the gas
โ— At RTP (room temperature) which is 25 degree and 1 atm of gas has a volume of 24dm3 or
24000cm3
โ— Number of moles = Volume of gas/ RTP (24)
โ— Volume of gas = 24 x number of moles
โ— Concentration
โ—‹ A concentration of 1 mole per dm3 is written as 1 mole/dm3
โ—‹ Concentration = mass/volume of (gas/solute)
โ—‹ Concentration = moles/volume of (gas/solute)
โ—‹ Moles = concentration x volume
โ— Limiting reactant
โ—‹ It is the reactant that is not in excess
โ—‹ 2SO2 + O2 โ†’ NA2CO3
2 moles 1.75 moles
โ—‹ Oxygen is not in excess which makes it the limiting reactant