# C3 Calculations

Titrations

• 1 - Write a balanced equation for the reaction
• 2 - Calculate the number of moles of the solution you know about
• 3 - Now you can work out the concentration of the other amount (Make sure to check the number of moles first)

Use the formula: Concentration (C) = Number of Moles (N) / Volume (V)

or C = NV

Remember: 1dm³ = 1000 cm³

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## Titration Calculations

Titrations

• 1 - Write a balanced equation for the reaction
• 2 - Calculate the number of moles of the solution you know about
• 3 - Now you can work out the concentration of the other amount (Make sure to check the number of moles first)

Use the formula: Concentration (C) = Number of Moles (N) / Volume (V)

or C = NV

Remember: 1dm³ = 1000 cm³

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## Energy Changes - Bond Calculations

Bond Energy Calculations

Energy change = energy used to break bonds - energy used to make bonds

So, for example, if you worked out (using information given in the question) that:

Energy used to break bonds = 2640kj

Energy used to make bonds = 3462

then, using this formula, the energy change would be 2640 - 3462 = -822kj.

If the energy change is negative, the reaction is exothermic, because the energy taken in to make the bonds is greater than the energy taken in to break the bonds.

If the energy change is positive, the reaction is endothermic, because the energy taken in to break the bonds is greater than the energy taken in to make them.

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## Empirical Formulae

Empirical Formulae

• 1 - Find the mass of each element in the products - except oxygen (so usually just carbon and hydrogen).

So, if you were doing hydrogen, and the product in the question was 9g   of water, you would do 2/18 (because water is 2/18ths hydrogen), then multiplied by 9 to work out how many grams of that element you have.

• 2 - Divide each element's mass by its atomic mass to work out the moles of each element

Continuing the example from before, hydrogen's Ar is 1. Therefore, you would do 1/1 = 1.

• 3 - Find the ratio of the two elements and use this to work out the formula.
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