There are two common ways to make a buffer: i) add relevant amounts of weak acid (or base) and conjugate base (acid) together, or ii) add strong acid to the weak base (or strong base to weak acid). a) what mass of na2co3(s) must be added to 250 ml of 0.30 m nahco3(aq) to give a ph 9.75 buffer solution, given pka (hco3) = 10.25? b) what mass of naoh(s) must be added to the same 250 ml solution of 0.30 m nahco3(aq) to give the same ph 9.75 buffer solution? c) sketch the speciation curve of this buffer for 2 ph units either side of the requested buffer ph. indicate quantitatively, the ph at which the cross-over point between the two species lies. in both cases, you may assume no change in volume when the solid is added.