the mass number of an atom tells you the the total number of protons and neutron in the nucleus

isotopes are atoms of the same elements with different numbers of neutrons

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Relative Formula Mass (RFM)

The symbol for the relative atomic mass is A_{r}.

This is calculated from the mass number and relative abundances of all the isotopes of a particular element.

The symbol for the relative formula mass is M_{r} and it refers to the total mass of the molecule.

To calculate the M_{r} of a substance, you have to add up the relative atomic masses of all the atoms present in the formula.

they are always measured in grams (g).

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Conservation of mass

The Law of Conservation of Mass states that no matter is lost or gained during a chemical reaction.

Mass is always conserved, therefore the total mass of the reactants is equal to the total mass of the products, which is why all chemical equations must be balanced.

The sum of the relative atomic/molecular masses of the reactants will be the same as the sum of the relative atomic/molecular masses of the products.

A precipitation reaction is one in which two solutions react to form an insoluble solid called a precipitate.

If the reaction flask is closed and no other substance can enter or leave the system, then the total mass of the reaction flask will remain constant.

For example, the reaction between calcium chloride and sodium sulfate produces a precipitate of calcium sulfate.

If carried out in a closed system then the mass before and after the reaction will be the same.

The balanced equation is:

CaCl_{2} + Na_{2}SO_{4} ⟶ CaSO_{4} + 2NaCl

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moles and their calculation

This is the mass of substance containing the same number of fundamental units as there are atoms in exactly 12.000 g of 12C.

The mole is the unit representing the amount of atoms, ions, or molecules and its symbol is mol.

One mol is the amount of a substance that contains 6.02 x 10^{23}particles (Atoms, Molecules or Formulae) of a substance (6.02 x 10^{23} is Known as the Avogadro Number).Example - 1 mole of Sodium (Na) contains 6.02 x 1023 atoms of Sodium.

how many moles are there in 25g of sodium oxide, NaO_{2 }

calculate the RFM of sodium oxide

RAM Na = 23 / RAM O =16

so the RFM of NaO_{2 = }(1 x 23) + (2 x 16) = 62g

number of moles = mass of substance (g) ÷ RFM (g)

25 ÷ 62 = 0.403 moles NaO_{2 }

answer = 0.403 moles of NaO_{2 }

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Balanced equations and their calculation

make sure that the formulae are correct for the chemicals involved

make sure that the equations balances using moles

using a balanced equation, you van calculate the amount of product that you could theoretically get

e.g how many grams of calcium oxide do you get forom the thermal decomposition of 200g of cacium carbonate? CaCO_{3 }= CaO + CO_{2}

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