Titrations

1) Using a pipette and a pipette filler, put some alkali into a conical flask. Add a few drops of an indicator.

2) Fill the burette with acid. This must be done below eye level so that you aren't looking up if acid spills over.

3) Add the acid to the alkali bit by bit.

4) Stop the moment the indicator changes colour.

5) Record the volume of acid used.

6) Repeat for reliability.

• many strong acids and alkalis are irritant, harmful or corrosive. Be careful, and wear gloves if necessary

• when filling the burette, do so below eye level in case some spills over]

• always wear goggles
  • NB in an exam, they generally assume that you will always wear goggles, so if you are asked to name some safety issues, don't say goggles. Unless you really have to.

You can often be asked about calculations to do with titration reactions. Here is a sample question (the answer, and a guide through it, is on the next card).

You have 25 cm^3 of sodium hydroxide (NaOH) solution at a concentration of 0.1 mol/dm^3.

You reacted this with

Find the concentration of the acid.

NB You will need to use moles to work this one out!

You have 25 cm^3 of sodium hydroxide (NaOH) solution at a concentration of 0.1 mol/dm^3.
You reacted this with

1) Write out the balanced equation --- 2NaOH + H2SO4 => Na2SO4 + 2H2O

2) Get all the units the same.
25 cm^3 = 0.025 dm^3 30 cm^3 = 0.03 dm^3

3) Work out moles of the one you know.
Moles = concentration x volume = 0.1 x 0.025 = 0.0025 moles of NaOH

4) Ratios
2 moles of NaOH ---- 1 mole of H2SO4
0.0025 moles ---- (0.0025 / 2) = 0.000125 moles

5) Formulae
0.000125 = concentration x 0.03 concentration = 0.0417 mol/dm^3