Question

5.A white salt on heating decomposes to give brown fumes and a residue is left behind.
a) Name the salt.
b) Write the equation for the decomposition reaction.
7. A few drops of H2SO4 are added into water before electrolysis. Why?
8. Oil and fat containing food items are flushed with Nitrogen.Give reasons.
4. Explain why :
When blue salt of CuSO4 is heated it becomes colourless.

Answer 1

a) and b) brow fumes - nitrates (extremely poisonous) and residue is yellow because i googled that question so here is the link:
http://www.meritnation.com/discuss/question/1033355
7. few drops of H2SO4 are added because H2SO4 is an electrolyte, it dissasociates compleatley in water and drasticaly increases its conductivity
8. i guess it is for preservation because oils and fats react with air
4. because blue salt of CuSO4 is copper sulphate hepta-hidrate and contains watter more exactly 7 molecules of water CuSO4*7H2O and when you heat it water is removed and the salt is white and again upon addition of water it becomes blue, it is often called "blue vitriol" and was used for prevention of grape leaves deseases

Answer 2

thank you for your kind help, Kryten.