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1.5.9States of Matter

Calculate Concentrations of Solutions — Cambridge IGCSE Chemistry 0620 Revision Notes & Topical Questions

5 min read 5 parts Lesson 18 of 30 Unit quiz

📚 Cambridge IGCSE Chemistry 0620 Hub / Topical Revision
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Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
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Part 1 of 5Key Terms

Concentration describes how much solute is present in a given volume of solution.

Solute
  • Solute The substance dissolved in a solvent, whose amount can be measured in grams or moles.
Solvent
  • Solvent The liquid that dissolves the solute, such as water, measured as a volume in cm³ or dm³.
Solution
  • Solution The mixture formed when a solute dissolves in a solvent, with a volume measured in cm³ or dm³.
Concentration
  • Concentration The amount of solute in a given volume of solution, usually expressed in mol/dm³ so that reactions can be compared.

Part 2 of 5Calculation Steps

1
Convert the volume into dm³ by dividing a value in cm³ by 1000, because concentration is always calculated in dm³.
2
Calculate the moles of solute using moles = mass ÷ Mr if the mass of solute is given.
3
Divide the moles of solute by the volume in dm³ to find the concentration in mol/dm³.
4
Use moles = concentration × volume when a question gives a concentration and asks for the amount of solute.

Part 3 of 5Units and Conversions

Units and Conversions
Cm³ to dm³
  • Cm³ to dm³ Divide by 1000, so 500 cm³ becomes 0.500 dm³.
Dm³ to cm³
  • Dm³ to cm³ Multiply by 1000, so 0.025 dm³ becomes 25 cm³.
Mass to moles
  • Mass to moles Divide the mass by Mr, so 4.0 g of NaOH is 0.10 mol because its Mr is 40.
Neutralisation
  • Neutralisation Use the balanced equation's mole ratio to link the moles of one reactant to the moles of the other before calculating an unknown concentration.

Part 4 of 5Worked Example

Question

  • Calculate the concentration in mol/dm³ of a solution made by dissolving 4.0 g of sodium hydroxide in water and making the volume up to 250 cm³.
  • Use Ar values Na = 23, O = 16 and H = 1.

  1. Mr of NaOH = 40, so moles = 4.0 ÷ 40 = 0.10 mol.
  2. Volume = 250 ÷ 1000 = 0.250 dm³.
  3. Concentration = 0.10 ÷ 0.250 = 0.40 mol/dm³.

Answer The concentration is 0.40 mol/dm³.

Part 5 of 5Exam Checklist & Tips

1.5.9 – Key Points for the Exam

  • Concentration The amount of solute in a given volume of solution, in mol/dm³.
  • Solute A substance dissolved in a solvent.
  • Solvent A liquid that dissolves a solute.
  • Solution A mixture of a solute dissolved in a solvent.
  • Neutralisation The reaction between an acid and a base to form a salt and water.

Common Mistakes

  • Putting a volume in cm³ directly into the concentration formula, which gives an answer 1000 times too large or too small.
  • Using the mass of solute instead of the number of moles in the concentration equation.
  • Ignoring the mole ratio from the balanced equation when two different substances react.
  • Using the volume of solvent added rather than the total volume of the solution made up to the mark.

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