chem
posted by Lena .
NH4Br has been dissolved into 1 L of water at 25 degrees celcius. the solution has a pH of 5.16. calculate number of grams of NH4Br.
I don't even know how to write the equation for this. Could someone please write the water + NH4 equation for me. Thanks :)

NH4^+ + HOH ==> NH3 + H3O^+
Ka = Kw/Kb = (H3O^+)(NH3)/(NH4^+).
You know Kw and Kb, and pH, you can calculate (H3O^+), (NH3) is the same, (NH4^+) = solve for this. Then M = moles/L to solve for moles and g = mols x molar mass to solve for grams. 
By the way, not the correct spelling of celsius.

Thanks a lot Dr Bob :)