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Here's a good question, that I was told appeared on a previous MCAT:
What is the pH of a 1.0 * 10^-8 M HCl solution?
What is the pH of a 1.0 * 10^-8 M HCl solution?
topdogg82 said:yeah jfleong is right on. when the acid/base conc. is extremely low, you have to take into account the contribution from water. so since its normally pH 7, it has 1x10^-7 [H+] conc. and adding the HCl adds 1x10^-8 to this, which gives a total of 11x10^-8 for [H+]. this is a pH of 6.95
Will Hunting said:I got this problem right from intuition. I knew it had to slightly less than 7. HOwever, in my gen chem class they never taught us to consider the acid dissociation of water when the acidic concentration is so low. If ph is 1e-7, we assumed it was 7. So in this case, 1e-8, based on our class the amount of [OH] would be 1 e-6 using using [H+][OH] = 1e-14. Consequently, since [OH] is greater one would think it would be basic. I feel cheated, i go to a large public big ten university and earned good grades and feel cheated. I mean we learned acid dissociation, but it was never used in the aforementioned situation. What book did you use, we used brown lemay bursten and it didn't cover this.