Question

Hydrazine is somewhat toxic. Use the following half-reactions to explain why household bleach (highly alkaline solutions of sodium hypochlorite) should not be mixed with household ammonia or glass cleansers that contain ammonia.

${\mathbf{ClO}}^{\mathbf{-}}\mathbf{+}{\mathbf{H}}_{\mathbf{2}}\mathbf{O}\mathbf{+}\mathbf{2}{\mathbf{e}}^{\mathbf{-}}\mathbf{\to }\mathbf{2}{\mathbf{OH}}^{\mathbf{-}}\mathbf{+}{\mathbf{Cl}}^{\mathbf{-}}$ $\mathit{\epsilon }\mathbf{°}\mathbf{=}\mathbf{0}\mathbf{.}\mathbf{90}\mathbf{}\mathbf{V}$

${\mathbf{N}}_{\mathbf{2}}{\mathbf{H}}_{\mathbf{4}}\mathbf{+}\mathbf{2}{\mathbf{H}}_{\mathbf{2}}\mathbf{O}\mathbf{+}\mathbf{2}{\mathbf{e}}^{\mathbf{-}}\mathbf{\to }\mathbf{2}{\mathbf{NH}}_{\mathbf{3}}\mathbf{+}\mathbf{2}{\mathbf{OH}}^{\mathbf{-}}$$\mathit{\epsilon }\mathbf{°}\mathbf{=}\mathbf{-}\mathbf{0}\mathbf{.}\mathbf{10}\mathbf{}\mathbf{V}$

Short answer

The reaction between ${\mathrm{ClO}}^{-}$ and ${\mathrm{NH}}_3$, in which${\mathrm{N}}_2{\mathrm{H}}_4$ is formed, is said to be spontaneous.

Step-by-step solution

Define Spontaneous reaction

A spontaneous reaction favors the build up of products at the conditions under which the reaction is occurring.

Explanation of why household bleach should not be mixed with household ammonia or glass cleansers that contain ammonia.

The reaction between${\mathrm{ClO}}^{-}$ ions and${\mathrm{NH}}_3$ is shown below as:

${\mathrm{ClO}}^{-}\left(\mathrm{aq}\right)+2\mathrm{N}{\mathrm{H}}_3\left(\mathrm{aq}\right)\to {\mathrm{Cl}}^{-}\left(\mathrm{aq}\right)+{\mathrm{N}}_2{\mathrm{H}}_4\left(\mathrm{aq}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)$

The cell potential ${\mathrm{E}}_{\mathrm{cell}}$, is said to be the measure of the potential difference between two half-cells in an electrochemical cell.

Now, using the half-reactions shown in the book.

Then, we can calculate the cell potential.

$$\begin{gathered} {\mathrm{E}}_{\mathrm{cell}}=0.90\mathrm{V}-(-0.10\mathrm{V}) \\ {\mathrm{E}}_{\mathrm{cell}}=1.00\mathrm{V} \end{gathered}$$

If the value of${\mathrm{E}}_{\mathrm{cell}}$ is positive, then the reaction is said to be spontaneous

This means that under standard conditions ${\mathrm{ClO}}^{-}$can oxidize ${\mathrm{NH}}_3$to toxic ${\mathrm{N}}_2{\mathrm{H}}_4$.

Therefore, the reaction between${\mathrm{ClO}}^{-}$ and ${\mathrm{NH}}_3$, in which${\mathrm{N}}_2{\mathrm{H}}_4$ is formed and is known to be spontaneous.