IGCSEChemistryCambridge (CIE)Revision Notes3. StoichiometryThe Mole & the Avogadro ConstantTitration Calculations

Titration Calculations (Cambridge (CIE) IGCSE Chemistry)

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Caroline Carroll

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Titration calculations

Extended tier only

  • Titrations are a method of analysing the concentration of solutions

    • Acid-base titrations are one of the most important kinds of titrations

  • Titrations can determine exactly how much alkali is needed to neutralise a quantity of acid – and vice versa

  • You may be asked to calculate:

    • The moles present in a given amount

    • The concentration or volume required to neutralise an acid or a base

  • Once a titration is completed and the average titre has been calculated, you can calculate the unknown variable using the formula triangle as shown below

Concentration, moles, volume formula triangle

Formula triangle showing the relationship between concentration, number of moles and volume of liquid

Worked Example

A solution of 25.0 cm3 of hydrochloric acid was titrated against a solution of 0.100 mol/dm3 NaOH. 

12.1 cm3 of NaOH was 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 = (begin mathsize 14px style volume over 1000 end style) x concentration

    • Moles of NaOH = 0.012 dm3 x 0.100 mol / dm3 = 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 (25.0 cm3 = 0.025 dm3)

  • Step 4: Find the concentration of the acid

    • Concentration = fraction numerator moles over denominator volume space open parentheses dm cubed close parentheses end fraction 

    • Concentration of HCl = fraction numerator 1.21 cross times 10 to the power of negative 3 end exponent space mol over denominator 0.025 space dm cubed end fraction= 0.0484 mol/dm3

Worked Example

25.00 cm3 of 0.15 mol / dm3 barium hydroxide, Ba(OH)2, was required to neutralise 12.80 cm3 of nitric acid, HNO3 , during a titration. Calculate the concentration of HNO3 that was used. Give your answer to 2 decimal places.

Ba(OH)2 (aq) + 2HNO3 (aq) → Ba(NO3)2 (aq) + 2H2O (l)

Answer:

  • Step 1: Calculate the number of moles of barium hydroxide 

    • Moles of barium hydroxide = concentration x volume (dm3) = 0.15 x 0.025 = 3.75 x 10–3 mols

  • Step 2: Using the equation, calculate the number of moles of nitric acid 

    • Moles of nitric acid = 3.75 x 10–3 x 2 = 7.5 x 10-3

    • The number of moles must be multiplied by 2 due to the 1:2 ratio

  • Step 3: Calculate the concentration of nitric acid

    • Concentration of nitric acid = fraction numerator 7.5 cross times 10 to the power of negative 3 end exponent over denominator 0.0128 end fraction= 0.59 mol / dm3 to 2 dp

  • Remember to convert cm3 to dm3 by dividing by 1000 

Worked Example

Calculating volume

Calculate the volume of 0.50 mol / dm3 nitric acid, HNO3, required to neutralise 25.00 cm3 of 0.80 mol / dm3 potassium hydroxide, KOH. Give your answer in cm3.

KOH (aq) + HNO3 (aq) → KNO3 (aq) + H2O (l)

Answer:

  • Step 1: Calculate the number of moles of potassium hydroxide

    • Moles of potassium hydroxide = concentration x volume (dm3) = 0.80 x 0.025 = 0.02 mols

  • Step 2: Using the equation, calculate the number of moles of nitric acid 

    • Moles of nitric acid = 0.02 mols

    • The ratio is 1:1 so the number of moles of nitric acid is the same

  • Step 3: Calculate the volume of nitric acid in cm3 

    • Volume of nitric acid =begin mathsize 14px style moles over concentration end style=  fraction numerator 0.02 over denominator 0.50 end fraction = 0.040 dm3

    • Volume of nitric acid = 0.040 dm3 x 1000 = 40 cm3

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    Caroline Carroll

    Author: Caroline Carroll

    Expertise: Physics Subject Lead

    Caroline graduated from the University of Nottingham with a degree in Chemistry and Molecular Physics. She spent several years working as an Industrial Chemist in the automotive industry before retraining to teach. Caroline has over 12 years of experience teaching GCSE and A-level chemistry and physics. She is passionate about creating high-quality resources to help students achieve their full potential.

    Stewart Hird

    Author: Stewart Hird

    Expertise: Chemistry Lead

    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 Topic Questions and revision materials for Save My Exams. Stewart specialises in Chemistry, but has also taught Physics and Environmental Systems and Societies.