Stoichiometric calculations
Summary Notes
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Calculations are done using a balanced equation.
The calculations involve reacting masses, volume of gases, concentrations of solutions and
volumes of solutions.
From the equation for a reaction you can tell:
how many moles of each substance take part
how many grams of each substance take part.
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The total mass does not change, during a chemical reaction.
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Calculating masses from equations
These are the steps to follow:
1 Write the balanced equation for the reaction. (It gives moles.)
2 Write down the Ar or Mr for each substance that takes part.
3 Using Ar or Mr, change the moles in the equation to grams.
4 Once you know the theoretical masses from the equation, you can then
find any actual mass.
Calculating gas volumes from equations
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The concentration of a solution is the amount of solute, in grams or
moles, that is dissolved in 1 dm3 of solution.
Finding the amount of solute in a solution
If you know the concentration of a solution, and its volume:
you can work out how much solute it contains, in moles.
Just rearrange the equation above:
amount of solute (mol) = concentration (mol / dm3) x volume (dm3)
you can then convert moles to grams, by multiplying the number of
moles by Mr.
Calculating concentration from an equation