Changing the concentration of the reactants

3 marks · Easy

A student dilutes 10.0 cm³ of 2.00 mol/dm³ sodium thiosulfate solution by adding water to make a total volume of 50.0 cm³.

(a)

State the formula used to calculate the concentration of the diluted solution.

[1 mark]

(b)

Calculate the concentration of sodium thiosulfate after dilution.

[2 marks]

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Show answer

(a) (volume of solute / total volume) × original concentration

(b) 0.40 mol/dm³

Common mistakes: Using incorrect volumes in formula

Show mark scheme and worked solution

Marking points

B1 (a) · 1 mark · States correct dilution formula: (volume of solute / total volume) × original concentration

M1 (b) · 1 mark · Substitutes values correctly into the formula.

A1 (b) · 1 mark · Calculates final concentration as 0.40 mol/dm³ (accept 0.4).

Worked solution

a) The formula is:

b) Substituting values: