Ok n=V*C right. And you want 750ml solution that is 0,5M. Then you need 0,75*0,5=0,375 mole. Now you know how much you need from the original HNO
3. Using the first formula V=n/C --> V=0,325/16= 0,023L or 23ml.
Edit: 3 answers. Should help you
[ 11-23-2002, 02:46 PM: Message edited by: WillowIX ]