Chemistry pH and concentration help please!!!?

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Nutrigrl

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Can somebody please explain the relationship between pH and the initial concentration of an acid solution.

Also, what is the difference between the pH of strong acid and the pH of a weak acid at the same concentration. Explain why this is so.
 
pH = -log[H+]
so the pH equals the negative log of the final concentration of H+ ions
the initial concentration is not used because depending on the acid, the acid will dissociate more or less
The initial concentration of H+ of a weak and strong acid may be the same but as the acids reach equilibrium the strong acid will dissociate more producing more H+ ions making the pH lower
 
Consider 0.001 M HA
If HA is a strong acid, it ionizes 100% to yield 0.001 M H+ and 0.001 M A-. The pH would be -log[H+] = -log(0.001) = 3.0.

If HA is a weak acid , it ionizes musch less than 100% (say 5 % for example) to yield 0.05 x 0.001 M H+ (0.00005 M) and 0.05 x 0.001 M A- (0.00005 M) with 0.95 x 0.001 M HA (0.00095 M) remaining non-ionized. The pH would be -log[H+] = -log(0.00005) = 4.3
 
The pH of a strong acid is alot lower than a weak acid (eg strong acid may = pH:1, wheras a weak acid pH: 3) at the SAME concentration. THis is because the strong acid completly dissociates (so is mostly product) wheras a weak acid may only slightly dissociate (product and reactant).

The pH is affected by the concentration (higher the concentration= lower the pH, or the more acidic it is).

To figure out pH from initial concentration (for example with H20 .....> h30+ + OH-) if you know the initial concentration of either

pH is simply = -log(concentration of H30+ or OH-)

To figure out the concentration from the pH, it is just 10^pH
eg if the pH was 3.3 you would go.....10^3.3 = concentration
 
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