Titration Calculations (Edexcel GCSE Chemistry): Revision Note
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Titration Calculations
Once a titration is completed and the average titre has been calculated, you can now proceed to calculate the unknown variable using the formula triangle as shown below
Formula triangle showing the relationship between concentration, number of moles and volume of liquid
The steps in a titration calculation are:
Step 1: Write out the balanced equation for the reaction
Step 2: Calculate the moles of the known solution given the volume and concentration
Step 3: Use the equation to deduce the moles of the unknown solution
Step 4: Use the moles and volume of the unknown solution to calculate the concentration
Worked Example
A solution of 25.0 cm3 of hydrochloric acid was titrated against a solution of 0.100 mol dm-3 NaOH and 12.1 cm3 were required for a complete reaction. Determine the concentration of the acid.
Answer:
Step 1: Write the equation for the reaction:
HCl (aq) + NaOH (aq) → NaCl (aq) + H2O (l)
Step 2: Calculate the number of moles of the NaOH
Moles = (volume ÷ 1000) x concentration
Moles of NaOH = 0.012 dm3 x 0.100 mol dm-3 = 1.21 x 10-3 mol
Step 3: Deduce the number of moles of the acid
Since the acid reacts in a 1:1 ratio with the alkali, the number of moles of HCl is also 1.21 x 10-3 mol
This is present in 25.0 cm3 of the solution
Step 4: Find the concentration of the acid
Concentration = moles ÷ volume
Concentration of HCl =1.21 x 10-3 mol ÷ 0.025 dm3 = 0.0484 mol dm-3
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