# Quantative Chemistry

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• Created by: Grace_B06
• Created on: 16-10-21 11:00

## Relative Formula Mass

All Compounds have a relative formula mass

• The relative formula mass (Mr) is just the relative atomic masses (Ar) of all the atoms in the molecular formula added together

You can calculate the % of mass of an element in a compound

• Percentage mass of element= Ar x no. of atoms of that element    x 100
•                                                 Mr of the compound

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## Moles

One mole of any substance is just an amount of that substance that contains an avogadro number of particles- so 6.02 x 1023

• One Mole of atoms or molecules of any substance will have a mass in grams equal to the relative formula mass (Mr) for that substance.
• No. of Moles=   Mass in g
•                            Mr

The mole is simply the name given to an amount of a substance

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## Conservation of Mass

In a Chemical Reaction Mass is always Conserved

• During a chemical reaction no atoms are destroyed and no atoms are created
• This means there are the same no. of and types of atoms on each side of the reaction equation.

If the mass seems to change there's probably a gas involved

• If the mass increases, its probably because one of the reactants is a gas thats found in air and all the products are solids, liquids or aqueous.
• If the mass decreases, its probably because one of the products is a gas and all the reactants are solids, liquids or aqueous.
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## The Mole and Equations

You can use Moles to calculate Masses in equations

• The big numbers in front of the chemical reactants and products in a balanced equation tell you how many moles there are.

You Can use this formula to work out mass/moles or formula of atomic mass with the below method:

1. Fill in grid with the data from the question (Grid should consist of balanced equation, then mass in g, then Ar/Mr and then moles)

2. Calculate formula mass of each compound

3.Calculate Number of moles of known value

4.  Use a ratio to find unknown moles

5.Calculate unkown mass

Or

1. Ignore any big numbers and fill out Ar/Mr row

2. Work out ratio (use big numbers)

3. Work out mass

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## The mole and Equations continued

Or

1. Ignore any big numbers and fill out Ar/Mr row

2. Work out ratio (use big numbers)

3. Work out mass

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## Limiting Reactants

Reactions stop when one reactant is used up

• Any other reactants that have been left behind are in Excess
• The reactant that's used up is called the Limiting Reactant
• The amount of product formed is Directly Proportional to the limiting reactant
• This is because if you add more reactant there is more reactant particles to take part in the reaction, which means more product particles
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## Concentration of solutions

Concentration is the amount of substance in one place

• The more solute there is in a solution, the more concentrated the solution

Solute is the substance dissolved

Solvent is the substance that dissolves a solute

Concentration can be measured in g/dm3

• Concentration= mass of solute(g)
•                           volume of solvent (dm3)
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