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 Ar.
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 Mr and it refers to the total mass of the molecule.
To calculate the Mr 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:
CaCl2 + Na2SO4 ⟶ CaSO4 + 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 1023particles (Atoms, Molecules or Formulae) of a substance (6.02 x 1023 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, NaO2
calculate the RFM of sodium oxide
RAM Na = 23 / RAM O =16
so the RFM of NaO2 = (1 x 23) + (2 x 16) = 62g
number of moles = mass of substance (g) ÷ RFM (g)
25 ÷ 62 = 0.403 moles NaO2
answer = 0.403 moles of NaO2
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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? CaCO3 = CaO + CO2
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