You are told what volume of stock solution of a component was added to a reaction mixture before adjusting to a final total volume. You are to calculate its final concentration.
You should aim to do these calculations in your head or on a scrap of paper (i.e. without a calculator). The following logic may be helpful:
The stock solution becomes diluted when a specific added volume is included in a larger total volume.
The dilution is equal to the total volume divided by the volume of stock added.
One multiplies the concentration of stock by this dilution factor to get the final concentration.
The final concentration is therefore:
(stock concentration x stock volume)/final volume
Always do a ‘sanity check’ on your answer. Is it the right order of magnitude? E.g. for a dilution factor of 8.5, round this up to 10 and check whether your answer is somewhere near one-tenth of the original concentration (rather than one-hundredth).