GCSEChemistryEdexcelRevision Notes5. Separate Chemistry 15.2 Quantitative Analysis5.2.3 Titration Calculations

Titration Calculations (Edexcel GCSE Chemistry)

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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

Concentration moles formula triangle, downloadable IB Chemistry revision notes

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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    Stewart

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    Stewart has been an enthusiastic GCSE, IGCSE, A Level and IB teacher for more than 30 years in the UK as well as overseas, and has also been an examiner for IB and A Level. As a long-standing Head of Science, Stewart brings a wealth of experience to creating Exam Questions and revision materials for Save My Exams. Stewart specialises in Chemistry, but has also taught Physics and Environmental Systems and Societies.