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Year 10
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Titrations: calculating an unknown concentration

I can calculate the concentration of an acid using results from a neutralisation titration.

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New
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Year 10
OCR
Higher

Titrations: calculating an unknown concentration

I can calculate the concentration of an acid using results from a neutralisation titration.

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Share activities with pupils
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Lesson details

Key learning points

  1. Data collected during a titration allows chemists to determine a solution’s unknown concentration.
  2. Concordant titres should be used when calculating a mean volume used to neutralise a solution.
  3. The coefficients in a balanced equation indicates the stoichiometry (i.e. molar ratio) between substances in a reaction.
  4. 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.

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.
Teacher tip

Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

Lesson video

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Starter quiz

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6 Questions

Q1.
What is a mole?
A unit of mass for small objects like atoms.
Correct answer: The amount of substance containing Avogadro’s number of particles.
The volume of gas under standard conditions.
The concentration of a solution in mol/dm³.
Q2.
How do you calculate the number of moles from mass?
number of moles = mass × relative formula mass
Correct answer: number of moles = mass ÷ relative formula mass
number of moles = mass + relative formula mass
number of moles = mass – relative formula mass
Q3.
Calculate the number of moles in 50 g of NaCl (relative formula mass of NaCl = 58.5).
Correct Answer: 0.85
Q4.
How do you calculate concentration in mol/dm³?
concentration = number of moles ÷ volume (in cm³)
concentration = number of moles × volume (in cm³)
concentration = number of moles × volume (in dm³)
Correct answer: concentration = number of moles ÷ volume (in dm³)
Q5.
How do you convert cm³ to dm³?
multiply the volume in cm³ by 1000
multiply the volume in cm³ by 10
Correct answer: divide the volume in cm³ by 1000
divide the volume in cm³ by 10
Q6.
Convert 250 cm³ to dm³.
Correct Answer: 0.25, 0.250, .25, .250

Exit quiz

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6 Questions

Q1.
Match the following key words to their definition.
Correct Answer:titration,A technique to find exact volumes of reacting solutions.

A technique to find exact volumes of reacting solutions.

Correct Answer:titre,The volume of titrant needed to reach the end point.

The volume of titrant needed to reach the end point.

Correct Answer:concordant,Readings within ±0.10 cm³ of each other.

Readings within ±0.10 cm³ of each other.

Correct Answer:coefficient,A number showing the ratio of substances in a reaction.

A number showing the ratio of substances in a reaction.

Correct Answer:mole,1 mole contains 6.02 × 10²³ particles.

1 mole contains 6.02 × 10²³ particles.

Q2.
Why are concordant titres important?
They ensure the solution has been accurately neutralised.
They show when the reaction is complete.
Correct answer: They allow chemists to calculate a precise average volume.
They help determine the end point of the titration.
Q3.
What is the stoichiometric ratio of HCl to NaOH in the balanced equation below? HCl + NaOH → NaCl + H₂O
Correct Answer: 1 : 1, 1:1, 1 to 1
Q4.
Calculate the number of moles in 18.5 g of NaOH (relative formula mass = 40).
Correct Answer: 0.463, 0.4625
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?
Correct answer: 0.25 mol/dm³
0.5 mol/dm³
0.125 mol/dm³
1 mol/dm³
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.?
Correct Answer: 0.267