A full set of notes for spec points 4.3 Quantitative chemistry:
4.3.1.1 Conservation of mass and balanced chemical equations
4.3.1.2 Relative formula mass
4.3.1.3 Mass changes when a reactant or product is a gas
4.3.1.4 Chemical measurements
4.3.2.1 Moles (HT only)
4.3.2.2 Amounts of substanc...
4311 conservation of mass and balanced chemical equations 4312 relative formula mass 4313 mass changes when a reactant or product is a gas 4314 chemical measure
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Chemistry Revision Notes – term 2
This file will contain:
4.3 Quantitative chemistry
4.3.1.1 Conservation of mass and balanced chemical equations
4.3.1.2 Relative formula mass
4.3.1.3 Mass changes when a reactant or product is a gas
4.3.1.4 Chemical measurements
4.3.2.1 Moles (HT only)
4.3.2.2 Amounts of substances in equations (HT only)
4.3.2.3 Using moles to balance equations (HT only)
4.3.2.4 Limiting reactants (HT only)
4.3.2.5 Concentration of solutions
, 4.3 Quantitative chemistry
4.3.1 Chemical measurements, conservation of mass and the
quantitative interpretation of chemical equations
4.3.1.1 Conservation of mass and balanced chemical equations quantitative interpretation of
chemical equations
The law of conservation of mass states that no atoms are lost or made during a chemical
reaction so the mass of the products equals the mass of the reactants
This means that chemical reactions can be represented by symbol equations which are
balanced in terms of the numbers of atoms of each element involved on both sides of the
equation
When a chemical reaction takes place the atoms are rearranged to make different
molecules, but no atoms can be made or destroyed
If the mass seems to change, there’s usually a gas involved
4.3.1.2 Relative formula mass
relative formula (molecular) mass(Mr)=Σrelative atomic
mass(Ar)
Relative atomic mass (Ar) is the mass of a singleatom on a scale on which the mass of an
atom of carbon-12 has a mass of 12 atoms mass units
The relative atomic mass does not have units
To calculate the relative formula mass of a compound, we need to know the relative
atomic masses (Ar) of the elements that make the compound
Molecular formula is also known as the actual formula mass
Then we multiply the A r values by the number of atoms of that element
in the compound
Then we multiply the A r values by the number of atoms of that element
in the compound
Relative molecular mass (M r) – also refered to as molar mass – is the mass of a single
molecule on a scale on which the mass of an atom of carbon-12 has a mass of 12 atomic
mass units
It is the sum of the relative atomic masses of the atoms in the numbers shown in the
formula
The Mr of a compound is equal to the mas in grams of 1 mole of the compound
In a balanced chemical equation, the sum of the relative formula masses of the reactants
in the quantities shown equals the sum of the relative formula masses of the products in
the quantities shown
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