I think it has to do with the fact it's a 2 step nuetralisation process. So half the acid is nuetralized at step 1 and the other half at step 2? I am not too sure. Maybe the overall equation might give some idea?
The D is is proton rich isnt it? It's just a hydrogen isotope.
The reason CDCl3 is used instead of CHCl3 as a solvent in Proton NMR is because it doesnt interfere with the results, dont think you need to know anything else, Deuterium is just an isotope of H, with double the mass.