hello again my angelic helpers
small american question to solve :
Which of the following mixtures results a PH=7.2 buffer ?
( phosphoric acid pKa1=2.1 pKa2=7.2, pKa3= 12.3 )
1) 100ml 1M Na2HPO4 + 100ml 1M NaH2PO4
2) 100ml 1M H3PO4 + 100ml 1M NaOH
3) 100ml 1M Na2HPO4 + 100ml 1M Na3PO4
4) 100ml 1M H3PO4 + 100ml 1M NaH2PO4
the answer should be 1 but what formula do i use ? i mean do i do it like this :
100ml * 1 ( only 1 H for Na2HPO4 ) 100
100ml * 2 (Two H for NaH2PO4 ) 200
then 200-100= 100 which means we will have 100 in a 200 solution
now what ?