Question

5g of copper(II)sulphate crystals are dissolved in water to form aqueous copper(II)sulphate solution. All the solution is then reacted with a 1.5 mol/dm³ of sodium hydroxide solution. A blue precipitate (solid) of copper(II)hydroxide was formed along with a colorless solution, sodium sulphate.

CuSO4 (aq)+ 2NaOH (aq) → Cu(OH)2 (s) + Na₂SO4 (aq)

1. Calculate the mass of the precipitate, Cu(OH)2 formed.
2. Calculate the volume of NaOH needed to react with 5 g of copper(II)sulphate.
3. Calculate the concentration (in mol/dm³) of sodium sulphate when 20 cm³ was formed.​

Answer 1

1. Amount of substance (CuSO4) = Mass of CuSO4/Molar mass of CuSO4
Calculate the amount of substance of Cu(OH)2, then multiply the molar mass of Cu(OH)2.
2. Calculate the amount of substance of NaOH. The concentration of NaOH is 1.5 mol/dm^3. Volume = Concentration/amount of substance.
3. cm^3dm^3
Calculate the mount of substance (Na2SO4).
Concentration = amount of substance/volume

The complete steps are as follows：