Perhaps just a little misunderstanding because we usually don't quote pH values when the acid is stronger than 1M (1M = pH = 0.) The pH USUALLY quoted as between 0-14 is for acid strengths between 1 and lower; however, for strong acids that ionize 100% such as 5M HCl, 10 M HCl, 17M HCl (as it comes out of the bottle), mathematically are negative values. We usually don't quote them as pH -1 or -10 because this sounds so unusual but the fact is that they are negative. The point I am making is that we don't use pH values in practice that are negative, instead we quote them as 10M or 17 M, but we could use the negative numbers if we wished.
