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C3 Part 1 (Relative atomic mass (The relative atomic mass is worked out…
C3 Part 1
Relative atomic mass
Different atoms have different masses. Atoms have such a small mass it is more convenient to know their masses compared to each other. Carbon is taken as the standard atom and has a relative atomic mass
The relative atomic mass is worked out using the following formula, illustrated for two isotopes, where the abundances are given in percentage values.
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The relative atomic mass of an element shows its mass compared with the mass of atoms of other elements. The relative atomic mass of carbon is 12, while the relative atomic mass of magnesium is 24. This means that each magnesium atom is twice the mass of a carbon atom.
Moles
Chemists measure the amount of a substance in a unit called ‘the mole’. This is a convenient way of counting atoms. It allows chemists to make predictions about the masses of different substances that are involved in reactions.
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Conservation of maths
Mass is never lost or gained in chemical reactions. We say that mass is always conserved. In other words, the total mass of products at the end of the reaction is equal to the total mass of the reactants at the beginning. This is because no atoms are created or destroyed during chemical reactions.
The principle of conservation of mass allows you to work out the mass of one substance in a reaction if the masses of the other substances are known.
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Relative formula mass
Relative atomic masses can be used to find the relative formula mass of a compound.
To find the relative formula mass (Mr) of a compound, you add together the relative atomic mass values (Ar values) for all the atoms in its formula.
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