how to prepare 500ml of a 0.75M Sodium Phosphate buffer solution at pH 7.5, how would you go about doing that?

Answer 1

I like to do these in millimoles. Although technically they are to be done with concentration in molarity, mmols works just as well and I think it is easier.
You have two equations. Let a = acid and b = base.
eqn 1 is a + b = 500 x 0.75 mmols.
eqn 2 is 7.5 = pKa2 + log (b/a)
where pKa2 is that of H3PO4.

Solve eqn 1 and eqn 2 simultaneously for a and b in millimoles.
Then convert mmols acid and mmols base to grams, weigh each and make the solution. The acid will be NaH2PO4 and the base will be Na2HPO4.