The easiest way to do this is to work a-d and see if they provide the same thing. Example:
What you have.
......H2PO4^- + OH^- ==> HPO4^2-
......0.75................0.6
Or....HPO4^2- + H^+ ==> H2PO4^-
.......0.6...............0.75
Now try a,b, etc and see which gives you one of the above. Post your work you get stuck. You notice right off the bat that a can't work. H2PO4^- + H^+ makes H3PO4 and that isn't what you want.
d can't possible work because
HPO4^2- + OH^- ==> PO4^3- and that isn't what you want. So I think the answer must be b or c.
A buffer is prepared consisting of 0.75 mol of sodium dihydrogenphosphate, NaH2PO4, and 0.60 mol of sodium hydrogenphosphate, Na2HPO4, dissolved in 600.0 mL of water.
The Ka for the dihydrogenphosphate ion is 6.2 x 10–8 at 25°C.
Which of the following is another possible way to make the buffer described in the data set above?
a.
Add 0.6 mol of HCl to 1.35 mol of NaH2PO4 in 600.0 mL of water.
b.
Add 0.6 mol of NaOH to 1.35 mol of NaH2PO4 in 600.0 mL of water.
c.
Add 0.6 mol of HCl to 1.35 mol of Na2HPO4 in 600.0 mL of water.
d.
Add 0.6 mol of NaOH to 1.35 mol of Na2HPO4 in 600.0 mL of water.
1 answer