Q21.27 P - Chemistry: Molecular Nature Of Matter And Change

Question

A voltaic cell is constructed with an ${\mathbf{\text{S}}}_{\mathbf{\text{n}}}\mathbf{\text{/}}{{\mathbf{\text{S}}}_{\mathbf{\text{n}}}}^{\mathbf{\text{2 + }}}$half-cell and a ${\mathbf{\text{Z}}}_{\mathbf{\text{n}}}\mathbf{\text{/}}{{\mathbf{\text{Z}}}_{\mathbf{\text{n}}}}^{\mathbf{\text{2 + }}}$ half-cell. The zinc electrode is negative. 

(a) Write balanced half-reactions and the overall reaction. 

(b) Diagram the cell, labelling electrodes with their charges and showing the directions of electron flow in the circuit and of cation and anion flow in the salt bridge.

Step-by-Step Solution

Answer

(a)$$\begin{gathered} \text{Oxidation :Sn}\to {\text{Sn}}^{\text{2 + }}{\text{ + 2e}}^{\text{ - }} \\ {\text{Reduction :Zn}}^{\text{2 + }}{\text{ + 2e}}^{\text{ - }}\to \text{Zn } \\ {\text{Overall :Sn + Zn}}^{\text{2 + }}\to {\text{Zn + Sn}}^{\text{2 + }} \end{gathered}$$

(b) Electrons travel from the anode to the cathode, while anions and cations flow from the cathode to the anode. The cathode is the $\text{Zn}$ electrode, and the anode is the $\text{Sn}$ electrode.

 

Step 1: Definition of Chemical Change and Electrical Work

Electrochemistry is a discipline of physical chemistry concerned with the relationship between electrical potential as a quantifiable and quantitative phenomenon and recognisable chemical change, with electrical potential as an outcome of a specific chemical change or vice versa.

 

Step 2: Write balanced half-reactions and the overall reaction.

(a) Balanced half-reactions and overall reaction

$$\begin{gathered} \text{ Oxidation :Sn}\to {\text{Sn}}^{\text{2 + }}{\text{ + 2e}}^{\text{ - }} \\ {\text{Reduction :Zn}}^{\text{2 + }}{\text{ + 2e}}^{\text{ - }}\to \text{Zn} \\ {\text{ Overall :Sn + Zn}}^{\text{2 + }}\to {\text{Zn + Sn}}^{\text{2 + }} \end{gathered}$$

Step 3: Diagram the cell, labelling electrodes with their charges and showing the directions

(b) Anions flow to the anode and cations flow to the cathode as electrons move from the anode to the cathode.

 The cathode is the $\text{Zn}$ electrode, while the anode is the $\text{Sn}$electrode.