[fiishh]

My supervisor has asked me to work out how much water to add to an acid to change its pH. The molarity of the acid is 9.3 (although this could be wrong as I tried to calculate it myself) and it has a pH of -0.97.

I want to have a series of dilutions, pHs 6, 5, 4 and 3.

Any help would be much appreciated 

[Arkcon]

Why not try some dilutions and see what happens?  If this is going to work at all, you may be surprised at how much you will have to dilute.  Can you give us the definition of the term: pH?  What formula relates pH and concentration?  The CRC (a common chemistry reference book) give the pH of common solutions of common strong acids and bases.  You don't know which of those you have, but you will gain a useful hint.

[Borek]

The molarity of the acid is 9.3 (although this could be wrong as I tried to calculate it myself) and it has a pH of -0.97.

That's based on two assumptions - acid is monoprotic and 100% dissociated. First is possible, second not so.

Also, pH is not just a minus log of the concentration, it is minus log of the activity - and activity equals concentration only in diluted solutions. 9.7 M is orders of magnitude too concentrated.