Division 4.3 Luff-Schoorl reagent: prepare the following solutions:

Copper II sulphate solution: dissolve 25 g of iron-free copper II sulphate pentahydrate (CuSO₄.5H₂O) in 100 ml water.

Citric acid solution: dissolve 50 g of citric acid monohydrate (C₆H₈O₇.H₂O) in 50 ml of water.

Sodium carbonate solution: dissolve 143.8 g of anhydrous sodium carbonate in about 300 ml of warm water and allow to cool.

Add the citric acid solution (4.3.2) to the sodium carbonate solution (4.3.3) in a one litre volumetric flask with gentle swirling. Swirl until effervescence ceases and then add the copper II sulphate solution (4.3.1) and make up to 1 000 ml with water. Allow the solution to stand overnight and then filter if necessary. Check the molarity of the reagent thus obtained by the method described in 6.1 (Cu 0·1 mol/litre; Na₂CO₃ 1 mol/litre).