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How to do titrations
- 25cm3 of sodium hydroxide (NaOH) at 1.5 mol/dm3 neutralises 21.5cm3 of
hydrochloric acid (HCl). Find the concentration of the acid in moles per
decimetre cubed (mol/dm3). Decimetres cubed is the same thing as litres
- So we know that in 1 litre of NaOH, we've got 1.5
moles. How much do we have in one millilitre?
- 1ml = 15/1000 = 0.0015 moles per ml (because there are
1000 millilitres in a litre, we divide by 1000.)
- But we don't have 1 ml of it, we have 25 ml of it, so we multiply by 25.
25 x 0.00515 = 0.0375 moles. Now, this tells us how much stuff we've got
in each chemical.
- Because there are the same number of moles in each chemical. If there weren't, and
the ratios were different, we would simply multiply or divide as needed.
- But, again, we don't have equal amounts of each substance, so we need to first find out the
concentration of 1 millilitre (cm3) of HCl. 0.0375/21.5 (because that's how much HCl we've
got) = 0.0017441 moles in a cm3 of HCl.
- The question is asking for the concentration of the HCl in moles per decimetre cubed, so we
multiply by 1000, because that's how many millilitres we've got in a litre. 0.0017441 x 1000 = 1.74
mol/dm3
- The question is asking for the concentration of the HCl in moles per decimetre cubed, so we
multiply by 1000, because that's how many millilitres we've got in a litre. 0.0017441 x 1000 = 1.74
mol/dm3
- Because there are the same number of moles in each chemical. If there weren't, and
the ratios were different, we would simply multiply or divide as needed.
- But we don't have 1 ml of it, we have 25 ml of it, so we multiply by 25.
25 x 0.00515 = 0.0375 moles. Now, this tells us how much stuff we've got
in each chemical.
- 1ml = 15/1000 = 0.0015 moles per ml (because there are
1000 millilitres in a litre, we divide by 1000.)
- First, we need to balance the equation: NaCl + HCl ==> NaCl + H2O
- From this, we can see that the ration of sodium hydroxide to hydrochloric acid is 1:1, so
for each mole of NaCl, there is 1 mole of HCl.
- From this, we can see that the ration of sodium hydroxide to hydrochloric acid is 1:1, so
for each mole of NaCl, there is 1 mole of HCl.
- So we know that in 1 litre of NaOH, we've got 1.5
moles. How much do we have in one millilitre?
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