Question

indicate all the species, in proper sequence, to which the copper in the powder is transformed during the course of the synthesis of CuCl

Answer 1

Copper exist as Cu(I), Cu(II) and Cu(III) which is rare. Cu (II) is most stable, Cu(III) is rare and Cu(I) is unstable and it is relatively sensitive to oxidation by moist air. The relative stabilities of each oxidation state depend on the nature of ligands and anions as well as the nature of the solvent medium.

In this experiment of preparing CuCl from CuCl2 atmost care should be taken because it is highly unstable in air or easily affected by moisture are often handled inside an inert atmosphere glovebox or glovebag, or in some cases a vacuum line.

Only those metals whose standard reduction potentials are lower than that of hydrogen react with non-oxidising acids like HCl and dil.H2SO4, and displace hydrogen from acids. since copper has higher reduction  potential (more positive) than hydrogen, and it does not react with HCl acid.

So in the process of making CuCl followings steps are followed,

1. 2Cu + O2 --> 2CuO

2. CuO(s) + 2 HCl(aq) → CuCl2(aq) + H2O(l)

3. In the 3rd step Sodium sulfite solution is added slowly to the Cu(II) chloride solution. Sodium sulfite solution act as reducing agent. reaction can be written as follows,

2Cu²⁺ + 2Cl^- + SO3^2- + H₂O --> 2CuCl + SO4^2- + 2H⁺

The Cu+ will immediately react with the available chloride ion to produce insoluble CuCl. And overall reaction can be written as follows,

2CuCl₂(aq) + Na₂SO₃(aq) + H₂O --> 2CuCl(s) + Na₂SO₄(aq) + 2HCl(aq)

now from above knowledge we can write species of copper transformed during course of reaction as

Cu(s)⁰--> Cu²⁺ --> Cu²⁺ --> Cu⁺