pH ValueDate: 09/05/2001 at 02:24:28 From: Urvashi Subject: pH value Hi! I would like to know the pH value of 0.1 N Sulphuric acid. Please help! Thanks. Date: 09/05/2001 at 15:59:48 From: Doctor Achilles Subject: Re: pH value Hi Urvashi, Thanks for writing to Dr. Math. Normally pH calculations can be very tedious. pH is related to the concentration of protons in the following way: pH = -log[H+] Where the log is base ten and [H+] is the concentration of H+ ions in moles/liter (or M). With sulfuric acid, this gets especially complicated, because the formula is H2SO4, so there are two protons that can dissociate, and you have to find the sum total of protons that dissociate. Fortunately, chemists have created Normality. Normality is similar to Molarity (moles/liter). There are two differences: 1) Molarity can measure the anything, Normality can only be applied to acids or bases. 2) The Molarity of a solution of H2SO4 or of anything else, is just the concentration of starting material in moles/liter. However, Normality is the concentration of H+ ions (for acids) or of OH- ions (for bases) that you get out of the solution. In other words, Normality normalizes for the fact that some acids and bases dissociate more than others, so the pH of a 1N solution of any acid is the same as a 1N solution of any other acid. A 1N solution of acid, by definition, has 1 mole/liter of H+ ions, and a 1N solution of base, by definition, has 1 mole/liter of OH- ions. In short, Normality measures the concentration of H+ ions or the concentration of OH- ions directly. From here, you should be able to figure out the pH of a 0.1N solution of acid. Hope this helps. If you have other questions, or you'd like to talk about this some more, please let me know. - Doctor Achilles, The Math Forum http://mathforum.org/dr.math/ |
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