If you know the concentration of one of the reactants present in the titration, you can work out the concentration of the other reactant.
Step 1: Convert volumes to dm3
25 cm3 of HCl = 25 ÷ 1000 = 0.025 dm3
20 cm3 of NaOH = 20 ÷ 1000 = 0.020 dm3
Step 2: Determine the number of moles of sodium hydroxide
moles of NaOH = concentration × volume
moles of NaOH = 0.5 × 0.020 = 0.010 mol
Step 3: Work out the number of moles of acid using the balanced equation HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l) In this reaction, one mole of HCl reacts with one mole of NaOH. This is a 1:1 ratio. Therefore, in our titration, 0.010 mol of NaOH must neutralise 0.010 mol of HCl. Step 4: Calculate the concentration of the acid concentration of HCl = number of moles ÷ volume concentration of HCl = 0.010 ÷ 0.025 = 0.4 mol/dm3
The concentration of the HCl is 0.4 mol/dm3
Other anion tests
Halide-To test for halide ions add nitric acid and sliver nitrate. If a halide is present it will form a coloured precipitate. KI-Yellow, BaCl-White, KBr-Cream.
Sulphate-Add a diltue HCl acid and a barium salt, it will form a white precipitate if sulphate ions are present.
Carbonate-Add dilute acid to the solution and collect any gas given off with a pipet. Place the pipet in the limewater, if it turns cloudy a carbonate is present.