Preparation of 57% HI Solution (Hydriodic Acid):
Boiling point: 125.5-126.5 deg C
Density 1.70 gr/ml
In a fume cupboard a 1.5 three neck flask is added a mixture of 480 grams of iodine and 600 mls of distilled water. The centre neck is added a sealed
stirring unit which leads almost to the bottom of the flask. The left neck is fitted and sealed with a glass tube which extends almost to the bottom
of the flask but does not touch the stirrer. This is connected to the hydrogen sulphide (H2S) generator. The right neck is fitted and sealed with a
short glass tube connected with a plastic tube to the bottom of an inverted funnel in a 5% sodium hydroxide solution.
The mixture is vigorously stirred and a stream of hydrogen sulphide (H2S) gas is passed rapidly in the iodine/water mixture as rapidly as it reacts
with the iodine. After several hours, 2-3 hours, the iodine disappears and the liquid assumes a yellow colour (sometimes almost colourless) and most
of the precipitated sulphur sticks together in the form of a hard lump. This liquid contains a mixture of HI, H2S and S. The liquid is now filtered
through a large funnel plugged with glass wool to remove the sulphur S. No need removing the dissolved H2S as this enhances the reductive power. Add a
few crystals of iodine to this HI/H2S solution and store at 0-5 deg C.
The sulfur mass can latter be removed by soaking in sodium sulfite solution.
|