Titrations: calculating an unknown concentration
Lesson details
Learning outcome
I can calculate the concentration of an acid using results from a neutralisation titration.
Key learning points
- Data collected during a titration allows chemists to determine a solution’s unknown concentration.
- Concordant titres should be used when calculating a mean volume used to neutralise a solution.
- The coefficients in a balanced equation indicates the stoichiometry (i.e. molar ratio) between substances in a reaction.
- The concentration of an unknown solution is found using the relationship: concentration = moles ÷ volume (in dm³).
Keywords
Titration - A technique in volumetric analysis that is used to find the exact volumes of solutions that react with each other.
Titre - The volume of titrant needed to reach the end point in a titration.
Concordant - Readings within a certain range. For titrations, these usually need to be within 0.10 cm³ of each other.
Coefficient - The number placed in front of a chemical formula to balance an equation; it shows the ratio of substances in a reaction.
Mole - 1 mole contains 6.02 × 10²³ particles. The mass of a mole of a substance is its relative mass expressed in grams.
Common misconception
Pupils use all of their titration results to calculate an average volume used during titration. Pupils also tend to miss steps in this multi-step process.
Stress the need to use concordant results when calculating an average volume for neutralising a solution via titration. Use a calculation grid to help keep each calculation step clearly organised.
Teacher tip
Provide pupils with a few different worked examples of the same titration calculation, including one that shows the correct working out. Challenge pupils to identify and correct the error in the other worked examples. Extend pupils to suggest how each error would affect the final concentration.
Licence
Lesson video
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Prior knowledge starter quiz
6 Questions
Q1.What is a mole?
Q2.How do you calculate the number of moles from mass?
Q3.Calculate the number of moles in 50 g of NaCl (relative formula mass of NaCl = 58.5).
Q4.How do you calculate concentration in mol/dm³?
Q5.How do you convert cm³ to dm³?
Q6.Convert 250 cm³ to dm³.
Assessment exit quiz
6 Questions
Q1.Match the following key words to their definition.
A technique to find exact volumes of reacting solutions.
The volume of titrant needed to reach the end point.
Readings within ±0.10 cm³ of each other.
A number showing the ratio of substances in a reaction.
1 mole contains 6.02 × 10²³ particles.
Q2.Why are concordant titres important?
Q3.What is the stoichiometric ratio of HCl to NaOH in the balanced equation below?
HCl + NaOH → NaCl + H₂O
Q4.Calculate the number of moles in 18.5 g of NaOH (relative formula mass = 40).
Q5.In a titration, 20 cm³ of 0.5 mol/dm³ HCl neutralises 40 cm³ of NaOH. The balanced equation is:
HCl + NaOH → NaCl + H₂O
What is the concentration of the NaOH?
Q6.In a titration, 25 cm³ of 0.4 mol/dm³ H₂SO₄ neutralises 75 cm³ of KOH. The balanced equation is:
H₂SO₄ + 2KOH → K₂SO₄ + 2H₂O
What is the concentration of the KOH in mol/dm³ to 3 d.p.?
To help you plan your 10 chemistry lesson on: Titrations: calculating an unknown concentration, download all teaching resources for free and adapt to suit your pupils' needs...
To help you plan your 10 chemistry lesson on: Titrations: calculating an unknown concentration, download all teaching resources for free and adapt to suit your pupils' needs.
The starter quiz will activate and check your pupils' prior knowledge, with versions available both with and without answers in PDF format.
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The assessment exit quiz will test your pupils' understanding of the key learning points.
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