Question

A greenish blue solid A is heated. It gives off a colourless gas B and leaves a black solid C (i) Name the Compound A? (ii) Name the compound C?

Answer 1

The compound A is probably copper carbonate and since you have not mentioned to what you are referring as C, I am considering the black solid as C, which is `"CuO"` OR copper(II) oxide.

Explanation:

See, most copper compounds are blue in colour. That gives a little hint that compound A may be a compound of copper.

Now coming to the heating part. Less electropositive metals like Silver, gold, and sometimes copper when heated give out volatile products. Since your question states that the gas liberated is colourless without any description of the nature of gas, I consider it to be either `"SO"_2` or `"CO"_2`.

`"SO"_2` comes from heating copper sulphate. But it does not seems quite a legit option as copper sulphate only on Red Hot Heating gives out `"SO"_2`.

So the most probable compound is `"CuCO"_3` and the underlying is the reaction.

`"CuCO"_3(s) -> "CuO"(s) + "CO"_2(g)`
`" "("blue")" " " "("black")`

Answer 2

A =`CuCO_3`
C= CuO

Explanation:

Some salts, as, for exaple thats of Copper (but sometimes olso these of Ni and Co) are greenisch blue: nitrate, carbonate chlorides and others. Almost all this salts , if you heat them decompose and leave a solid (CuO is black) and give an anidride. NOx aren't colourless while `CO_2` is . I think the compound A is `CuCO_3` but to be sure, you should make other tests