Volumetric analysis of NaCl

The chlorides were precipitated in the form of silver chloride, at a slightly alkaline pH in the presence of potassium chromate, as indicator. The end-point of titration was visualised by the formation of a redbrick precipitate of silver chromate. Five grams of the sample was weighed (Shimadzu®, model AY220) on a porcelain dish and then carbonised on an electric sheet. The sample was then incinerated in a muffle oven at 550°C, then cooled. Thirty millilitres of hot water was then added and stirred with a glass stick. The solution was transferred with a funnel into a 100-ml volumetric flask. The capsule, glass stick and funnel were washed with another two 30-ml portions of hot water. The solution and wash water were then transferred to the volumetric flask, cooled, flushed, shaken and filtered. A 10-ml aliquot was transferred into a 125-ml Erlenmeyer flask with a pipette. Two drops of 10 % potassium chromate solution were added as an indicator, then titrated with 0·1 ml silver nitrate solution until a redbrick colour appeared.