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Year 10
AQA
Higher

Titrations: calculating an unknown concentration

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

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New
New
Year 10
AQA
Higher

Titrations: calculating an unknown concentration

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

Download all resources
Share activities with pupils

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).

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.

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.

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).

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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