Complete and balace the following chemical reaction:
(i). `Na_2CO_3` is added to a solution of copper sulphate.
`CuSO_4+Na_2O_3+H_2Oto…+Na_2SO_4`….
(ii). Potassium dichromate and concentrated HCl are heated together.
`K_2Cr_2O_7+"HCl"toKCl+.....+.....+....H_2O`
(iii). Copper reacts with `HNO_3` to give NO and `NO_2` in molar ratio of `2:1`
`Cu+HNO_3to...+NO+NO_2+`.....

Explanation

(i). `CuSO_4+Na_2CO_3+H_2OtoCu(OH)_2darr+Na_2SO_4+CO_2uarr`
(ii). Chlorine is evolved.
`K_2Cr_2O_7+14"HCl"to2KCl+2CrCl_3+7H_2O+3Cl_2uarr`
(iii). `CutoCu^(2+)+2e^(ɵ)]xx3`
`underline(4H^(o+)+3e^(ɵ)+NO_3^(ɵ)toNO+2H_2O]xx2)`
`underline(3Cu+8^(o+)+2NO_3^(ɵ)to3Cu^(2+)+2NO+4H_2O)`
`3Cu+8HNO_3(dil)to3Cu(NO_3)_2+4H_2O` ..(i)
`CutoCu^(2+)+2e^(ɵ)`
`underline(2H^(o+)+e^(ɵ)+NO_3^(ɵ)toNO_2+H_2O]xx2)`
`underline(3Cu+4H^(o+)2NO_3^(ɵ)TOCu^(2+)+2NO_2+2H_2O)`
`Cu+4HNO_3` (conc.) `toCu(NO_3)_2+2NO_2+H_2O` ..(ii)
To get No and `NO_2` in the molar ratio of `2:1` multiply equation (i) by 2 and then add equation (i) and (ii) to get `7Cu+20KNO_3to7Cu(NO_3)_2+4NO+4NO_2+10H_2O`
Hence, number of moles of `Cu=7`
Number of moles of `KNO_3=20`