0.05 molar standard solution of calcium.

Weigh out 5.004 g of dry calcium carbonate. Place it in a beaker with 100 ml of water. Progressively stir in 120 ml of approximately 1 M hydrochloric acid (4.12).

Bring to the boil in order to drive off the carbon dioxide, cool, transfer quantitatively into a graduated one-litre flask, make up the volume with water and mix. Check this solution against the EDTA solution (4.2) following analytical procedure (8.3). 1 ml of this solution should contain 2.004 mg of Ca (=2.804 mg of CaO) and should correspond to 1 ml of the 0.05 M EDTA solution (4.2).