<p>Ok, this has to do with dilution/titration.
I'm working out of the Kaplan prep book. Here is an example of a questions:</p>
<p>What volume of water would be needed to dilute 50mL of 3M HCl solution to 1M?</p>
<p>so, MV=MV: 50x3=1xV, V=150. However they say the answer is 100, cuz you already have 50 ml of water (100+50=150). Is this what the question means? It kinda sounds like they would have to say how much water would have to be added for an answer of 100 to be correct. But I guess not?? Is it cuz of the ''to dilute phrases?''</p>
<p>Also, I remember learning when you have a strong Polyprotic acid like H2PO4, and u are going to do a titration/dilution, then you have to factor in the the amount of H's in the MV=MV equation? Is this right, if not, when?</p>
<p>Here is an example question from Kaplan:</p>
<p>What volume of water would be needed to dilute 50ml of 3M H2SO4 TO .75 ml?</p>
<p>They do it just by: 50 x 3 = .75 x V, and u get V=200. However the FINAL answer they have is 150, cuz 150 is added to 50 to get 200.</p>
<p>I'm in AP Chem, and don't remember this kind of methodoolgy. Help, please, haha.</p>