Chemistry

Ammonia solutions are weakly basic because $NH_3$ accepts protons from water, establishing an equilibrium. The key is to first find the molarity of ammonia from the mass percentage and density, then use the $K_b$ relationship (derived from $K_w$ and the given $K_a$) to find $[OH^-]$ from the weak base equilibrium. Once you have $[OH^-]$, finding $[H^+]$ is just one step using the water ionization constant.

Ammonia solutions are weakly basic because $NH_3$ accepts protons from water, establishing an equilibrium. The key is to first find the molarity of ammonia from the mass percentage and density, then use the $K_b$ relationship (derived from $K_w$ and the given $K_a$) to find $[OH^-]$ from the weak base equilibrium. Once you have $[OH^-]$, finding $[H^+]$ is just one step using the water ionization constant.