Missing question: calculate concentration of OH⁻ ion.
Chemical reaction: Mg(OH)₂ + 2NH₄Cl → MgCl₂ + 2NH₄OH.
pH = 9.10.
[H+]
= 10∧(-pH).
[H+]
= 10∧(-9.10).
[H+] = 7.94·10⁻¹⁰ M.
[H+] · [OH⁻] = 10⁻¹⁴ M².
[OH⁻] = 10⁻¹⁴ M² ÷ 7.94·10⁻¹⁰ M.
[OH⁻] = 1.25·10⁻⁵ M.
