Chemistry · Ionization of water, pH scale, common ion effect, hydrolysis of salts and pH of their solutions, the solubility of sparingly soluble salts, solubility products and buffer solutions

1.2 mol of \) is added to 0.8 moles of and the solution is diluted to one litre,

1.2 mol of \( \boldsymbol{C H}_{3} \boldsymbol{N} \boldsymbol{H}_{2}\left(\boldsymbol{p} \boldsymbol{K}_{\boldsymbol{b}}=\boldsymbol{3} . \boldsymbol{3}\right) \) is added to 0.8 moles of \( H C l \) and the solution is diluted to one litre, resulting \( \boldsymbol{p} \boldsymbol{H} \) of solution is:

  • A. 10.7
  • B. 3.6
  • C. 10.4
  • D. 11.3

Step-by-step solution

HCl reacts with CH3NH2 to form CH3NH3+; after reaction, [CH3NH2] = 0.4 M and [CH3NH3+] = 0.8 M. Using Henderson-Hasselbalch for base: pOH = pKb + log([salt]/[base]) = 3.3 + log(2) ≈ 3.6. pH = 14 - pOH ≈ 10.4.
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