Question

4-Methylphenol, \(\mathrm{CH}_{3} \mathrm{C}_{6} \mathrm{H}_{4} \mathrm{OH}\left(\mathrm{p} \mathrm{K}_{2}\right.\) 10.26), is only slightly soluble in water, but its sodium salt, \(\mathrm{CH}_{3} \mathrm{C}_{6} \mathrm{H}_{4} \mathrm{O}^{-} \mathrm{Na}^{+}\), is quite soluble in water. In which solution(s) will 4-methylphenol dissolve? (a) Aqueous \(\mathrm{NaOH}\) (b) Aqueous \(\mathrm{NaHCO}{ }_{3}\) (c) Aqueous \(\mathrm{Na}_{2} \mathrm{CO}_{3}\)

Short answer

Answer: 4-methylphenol will dissolve in all three given solutions: (a) Aqueous NaOH, (b) Aqueous NaHCO₃, and (c) Aqueous Na₂CO₃.

Step-by-step solution

Identify pKₐ values of the ions in the solutions

The pKₐ values for the ions formed in the given solutions are: (a) OH⁻ formed in NaOH: 15.7 (strong base) (b) HCO₃⁻ formed in NaHCO₃: 10.3 (weak base) (c) CO₃²⁻ formed in Na₂CO₃: 10.3 (weak base)

Compare pK₂ value of 4-Methylphenol with ions' pKₐ values

We are given the pK₂ value for 4-Methylphenol: 10.26 Now, let's compare this to the pKₐ values of the ions in the solutions: (a) OH⁻ (from NaOH): pKₐ = 15.7 > 10.26 (b) HCO₃⁻ (from NaHCO₃): pKₐ = 10.3 > 10.26 (c) CO₃²⁻ (from Na₂CO₃): pKₐ = 10.3 > 10.26

Determine in which solutions 4-methylphenol dissolves

Since the pKₐ values of the ions in all three solutions are greater than the pK₂ value of the 4-methylphenol, it will dissolve in all the given solutions: (a) Aqueous NaOH (b) Aqueous NaHCO₃ (c) Aqueous Na₂CO₃