Calcium oxide hydrochloric acid
The lime should have a purity of at least 70% by weight of CaO when tested as follows:
- Take one gram of powdered lime, accurately weighed, in a platinum crucible. Place it in an oven maintained at 105 + 20C until, on cooling and weighing, constant mass is obtained.
- Heat the crucible first gently and then ignite in a muffle furnace at 10000 Cool the crucible in a desiccator and weigh to a constant mass.
- Transfer the ignited lime, to a beaker, add 50 ml of water and mix well. Add 10 to 15 ml of concentrated hydrochloric acid, and boil for 15 min. Filter, wash with hot water, ignite and weight to constant mass.
- To the filtrate, add concentrated hydrochloric acid, if necessary, in sufficient amount to make the total amount equivalent to 10 to 15 ml of concentrated hydrochloric acid. Add a few drops of nitric acid and boil. Dilute to 200-250 ml. Add slight excess of ammonium hydroxide and keep just below the boiling point until the odour of ammonia is barely perceptible. Filter off the iron and aluminium hydroxide while hot, collecting the filtrate in a 250 ml volumetric flask. Wash with hot water. Ignite the residue in a platinum crucible, blast, cool in a desiccators and weigh as aluminium oxide and ferric oxide. Make up the filtrate to 250 ml.
- Pipette out 50 ml of the filtrate in a beaker and dilute to 100 ml. Heat to boiling and add slowly about 35 ml of boiling ammonium oxalate solution. Continue boiling for 2 or 3 min and allow the precipitated calcium oxalate to settle for half an hour.
- Filter the precipitated calcium oxalate through filter paper. Wash thoroughly with small portions of dilute ammonium hydroxide (1 N) and then with hot water until the washing do not decolourise a hot dilute potassium permanganate solution in the presence of dilute sulphuric acid.
- Puncture the filter paper and transfer the precipitate to the beaker already used for precipitation with a fine jet of hot water. Add about 50 ml of dilute sulphuric acid, heat to 600C and titrate with standard potassium permanganate solution with constant stirring. Towards the end of the titration, introduce the filter paper which was used for filtration into the titration vessel and carry out the titration till the end point is reached.
- Carry out a blank with all reagents following...
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