Chapter U1, Problem 18STP

Interpretation Introduction

Interpretation:

The charge of the copper atoms in the copper solid in given copper cycle needs to be determined.

Concept introduction:

The oxidation state of an atom or ion indicates the charge on it if it forms ion. The oxidation state of ions represents the number of electrons gain or lost by an ion.

The sum of oxidation state of all bonded atoms in a molecule is always zero as molecules are neutral with zero charge on it.

Answer to Problem 18STP

Option (C) is correct option.

Explanation of Solution

Reason for correct option: Copper cycle is a series of conversion of solid to copper to again back to solid copper after different chemical changes. The reactions can be summarized as:

$\begin{array}{l}{\text{Cu}}_{\text{(s)}}{\text{+ 4HNO}}_{\text{3(aq)}}\stackrel{}{\to }{\text{Cu(NO}}_{\text{3}}{\text{)}}_{\text{2(aq)}}{\text{+ 2 NO}}_{\text{2(g)}}{\text{+ 2H}}_{\text{2}}{\text{O}}_{\text{(l)}}\\ {\text{Cu(NO}}_{\text{3}}{\text{)}}_{\text{2(aq)}}\text{+ 2 NaOH(aq)}\stackrel{}{\to }{\text{ Cu(OH)}}_{\text{2(aq)}}{\text{+ 2 NaNO}}_{\text{3}}{}_{\text{(aq)}}\\ {\text{Cu(OH)}}_{\text{2(aq)}}\stackrel{}{\to }{\text{CuO}}_{\text{(s)}}{\text{+H}}_{\text{2}}{\text{O}}_{\text{(l)}}\\ {\text{CuO}}_{\text{(s)}}{\text{+ H}}_{\text{2}}{\text{SO}}_{\text{4(aq)}}\stackrel{}{\to }{\text{CuSO}}_{\text{4(aq)}}{\text{+H}}_{\text{2}}{\text{O}}_{\text{(l)}}\end{array}$

In copper solid ${\text{Cu}}_{\text{(s)}}$ the charge on atom must be zero as it is standard state of copper. The charge or oxidation state of all elements in their standard state is always zero.

Conclusion

Reasons for incorrect options:

${\text{Cu}}_{\text{(s)}}$ is the standard state of copper so it must be neutral.