Copper(II) and iron (II)?

Question

when a certain green powder is heated, it produces a black power A and a gas B. B gives a white ppt. with limewater.

Upon adding dilute sulphuric acid to the black podwer and filtering, a blue solution is obtained.

if the green powder was iron(II) carbonate. and the black solid is iron(ii) oxide, how did blue solution copper(II) come into the picture?? or was the green powder copper(II) all along? i dont understand how the green iron(II) became copper(II). confusing

Answer 1

Green is usually an indication you have copper (II),l not iron (II).  Iron (II) compounds tend to be yellow or orange.

The green compound was probably copper(II) carbonate.  Decomposition of metallic carbonates produce metallic oxides and CO2.  Copper(II) oxide is black.  Iron(II) oxide is NOT black.

CuCO3 = CuO + H2O

The black copper(II) oxide then reacted with the sulfuric acid (double replacement reaction) to produce the blue copper(II) sulfate.

CuO + H2SO4 = CuSO4 + H2O

There is no evidence iron(II) was present

Answer 2

You can't convert  iron ions to copper ions in a chemical process.

The idea that the green powder is an carbonate which decomposes to metal oxide and carbon dioxide is right.  

But I think the green powder is copper(II) carbonate and not iron(II) carbonate. Both salts are green and their corresponding oxides are black. Only the sulfates, which you get from the reaction of the oxide with sulfuric acid, have different colors: copper(II) sulfate is blue, while Iron(II) sulfate is green.