What is the pH of a 1.00 x 10–9 molar solution of HCl?
9
5
6
6.8
7
And its not 9 or 5. Please list how this is solved. Thanks.
2007-07-25 12:43:11 · 5 answers · asked by Anonymous in Science & Mathematics ➔ Chemistry
The answer is actually 6.99 or 7. Remember, HCl is an acid so, it should not be 9. You actually need to take into account the pH of water to get the answer.
molar concentration of HCl + molar concentration of H2O
So, 1.00 x 10–9 + 1.00 x 10–7 = 1.01 x 10-7
Get the - log of the answer and you'll get 6.99 or 7.
2007-07-25 13:13:14 · answer #1 · answered by titanium007 4 · 2⤊ 0⤋
the last two people are correct. An acidic solution cannot have a pH greater than 7.
Remember that water always autoionzies into H^+1 and OH^-1 ions. At 25oC, since the K of water = 1.00 x 10^-14 that means that the H^+1 concentration and OH^-1 concentration are 1.00 x 10^-7
Normally, we completely ignore the autoionization of water, because the acid in solution generally completely outweighs the presence of H^+ ions that water naturally produces. For example, if the concentration of HCl was 0.10 M then the total amount of H^+1 ions would be 0.10 + 0.0000001 which sig fig wise = 0.10!
Since the concentration of your acid is so itty bitty teeny tiny, the autoionization of water is actually what dominates here -
1.00 x 10^-7 + 1.00 x 10^-9
0.000000100
+0.00000000100
_________________
0.000000101 M for H^+1 ions
1.01 x 10^-7 M
pH = -log [H^+1]
pH = -log [1.01 x 10^-7]
pH = 6.99567 = 7
2007-07-25 20:38:53 · answer #2 · answered by Anonymous · 0⤊ 0⤋
The answer is 7. Normally, in an aqueous solution of HCl the major species are H+ and Cl- and H2O. However, in this case the amount of HCl in solution is so small that it has no effect. The only major species is H2O. Therefore, the pH will be that of pure water. pH of H2O is 7.
2007-07-25 19:56:07 · answer #3 · answered by Nicole 1 · 2⤊ 0⤋
It would be a pH of 7. The H+ would increase to 1.02x10-7 with the acid addition, but this would be a miniscule change.
2007-07-25 19:48:05 · answer #4 · answered by cattbarf 7 · 1⤊ 0⤋
you take the negative log of the number in question, give me a sec, ill go grab my calculator out of the car and tell you what the answer is in this specific case.
There is a possibility that I am wrong, but I would say I'm 99% sure the answer is 9.
-log[(1.0)*(10^-9)] = 9.
2007-07-25 19:46:53 · answer #5 · answered by stephen r 3 · 1⤊ 0⤋