Assay copper using fluoride and Sodium Thiosulphate (Hypo) to titrate with, you’ll need:

• 8 cc’s of nitric acid are placed on given weight of sample and heated on the hot plate.
• Potassium Chlorate is added when all brown fumes have been driven off.
• 10 cc’s water are added and solution is again heated then taken off the hot plate and place in a cold water bath to cool.
• Ammonia is added, drop by drop until solution begins to turn brown ; Acetic acid is then added ( about 15 cc’s). Solution is then allowed to cool a second time.
• Sodium fluoride is then added.
• Potassium iodide is now added and the s solution is titrated with sodium thiosulphate (Hypo).

When the solution begins to turn brown or Pale Yellow add a few drops of prepared starch solution which turns the solution a purple brown.
Now carry on titration.  As the solution turns light purple add hypo drop by drop until purple disappears completely.

Notes On this copper assay method.

Ammonia is added here to partly precipitate the iron.
Sodium fluoride is added to form a substance which liberates the iodide.
Sodium thiosulphate reacts on the free iodide which the copper fluoride has liberated.
The cc’s used are taken multiplied by the standard.