Question

The ionization constant of phenol is $$1.0\times {10}^{-10}$$ . What is the concentration of phenolate ion in 0.05 M solution of phenol? What will be its degree of ionization if the solution is also 0.01 M in sodium phenolate?

Answer 1

Hint: Phenol is an organic aromatic compound with molecular formula $$C_6{H}_{5}OH$$. It is a volatile white, crystalline solid. The molecule consists of a group of phenyls $$(-C_6{H}_5)$$ bound to a group of hydroxy $$(-OH)$$. Mildly acidic, it needs careful handling because chemical burns will occur.

Complete step-by-step answer:
Calculation of Phenolate Ion concentrations:
$$\alpha =\sqrt{{\displaystyle \frac{K_{\alpha }}{C}}}$$
Here,
$$\begin{gathered} K_{\alpha }=1.0\times {10}^{-10} \\ C=0.05M \\ \therefore \alpha =\sqrt{{\displaystyle \frac{1.0\times {10}^{-10}}{0.05}}}=0.44\times {10}^{-4} \end{gathered}$$
Hence, concentration of phenolate ion $$[C_6{H}_5{O}^{-}]$$
$$\begin{gathered} =C\times \alpha =0.05\times 0.44\times {10}^{-4} \\ =2.2\times {10}^{-6} \end{gathered}$$
Now we have to calculate the degree of ionization in the presence of sodium phenolate
Let $$\alpha$$ be the degree of phenol dissociation where 0.01 M of phenolate ion is present.
                                    $$C_6{H}_{5}OH\rightleftharpoons C_6{H}_5{O}^{-}+H^{+}$$
Concentration $$(1-\alpha )0.05\text{ 0}\text{.05}\alpha \text{ 0}\text{.05}\alpha$$
Hence,
$$[C_6{H}_{5}OH]=0.05(1-\alpha )=0.05$$
$$[C_6{H}_5{O}^{-}]=0.05\alpha +0.01\approx 0.01M$$
$$[H_3{O}^{+}]=0.05\alpha$$
We get,
$$K_{\alpha }={\displaystyle \frac{(0.01)(0.05\alpha )}{0.05}}$$
$$\Rightarrow {10}^{-10}=0.01\alpha$$
$$\Rightarrow \alpha ={10}^{-8}$$
Therefore, degree of ionization in the presence of sodium phenolate is $${10}^{-8}$$

Note: An ion is a molecule or atom with a net electric charge. Because the charge of the electron (considered negative by convention) is equal and contrary with that of the proton (considered positive by convention), the net charge of an ion is non-zero because its total amount of neutrons is unlike the total number of protons it contains.
Ionization is the mechanism by which an atom or molecule, often in combination with certain chemical modifications, acquires a negative or positive charge by acquiring or losing electrons. The electrically charged atom or molecule arising from this is called an ion.
Sodium phenoxide (sodium phenolate) with the formula $$NaO{C}_6{H}_5$$ is an organic compound. This is a solid crystalline material. The anion, phenoxide, also called phenolate, is the phenol's conjugate base. Some other organic compounds, such as aryl ethers, are used as precursors.