In estimation of copper and nickel why we are using volumetric for copper and gravimetric for nickel seperately?

Answer 1

It is simply because they could not be found together!! copper can be estimated by treating with potassium iodide and iodine will be liberated in the reaction which is titrated against sodium thiosulphate during the reaction we will add sulphuric acid to prevent the hydrolysis of copper sulphate and we follow by, adding ammonia to neutralize sulphuric as it may hinder the reation between iodide and copper!! now again we will add acetic acid to neutralize ammonia.. and the indicator is added at the last because it will get absorbed with the iodine!! now atlast we add ammonium, thiocyanate to prevent the excess of iodine getting added to copper iodide. end point is disappearance of blue color.

Answer 2

Volumetric analysis is preferred for copper because copper forms colorful complex compounds which can be easily detected by color change during titration. Gravimetric analysis is preferred for nickel because nickel forms insoluble compounds which can be easily precipitated and then weighed to determine the amount of nickel present accurately.