Ch17_pH_2 - MORE ABOUT WATER H2O can function as both an...

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Unformatted text preview: MORE ABOUT WATER H2O can function as both an ACID and a BASE. 1 MORE ABOUT WATER Autoionization OH-OH + H33O+ HO 2 + Calculating [H3O+] & [OH--] 3 3 You add 0.0010 mol of NaOH to 1.0 L of pure water. Calculate [H 3O+] and [OH -]. Solution 2 H2O(liq) ¸ H3O+(aq) + OH-(aq) O(liq) aq) aq) oC Kw = [H 3O+] [H [OH -] = 1.00 x 10 -14 at 25 at In a neutral solution [H 3O+] = [OH-] neutral solution In pure water there can be AUTOIONIZATION so Kw = [H3O+]2 = [OH-]2 [H [OH and so [H 3O+] = [OH -] = 1.00 x 10 -7 M Le Chatelier predicts equilibrium shifts to the ____________. [H3O+] < 10-7 at equilibrium. at Set up a concentration table. + Calculating [H3O+] & [OH--] 3 4 + Calculating [H3O+] & [OH--] 3 5 + [H3O+], [OH--] and pH 3 6 You add 0.0010 mol of NaOH to 1.0 L of pure water. Calculate [H 3O+] and [OH -]. Solution 2 H2O(liq) ¸ H3O+(aq) + OH-(aq) O(liq) aq) aq) 0 0.0010 initial change equilib +x x +x 0.0010 + x You add 0.0010 mol of NaOH to 1.0 L of pure water. Calculate [H 3O+] and [OH -]. Solution 2 H2O(liq) ¸ H3O+(aq) + OH-(aq) O(liq) aq) aq) [H3O+] = Kw / 0.0010 = 1.0 x 0.0010 10 -11 M A common way to express acidity and basicity is with pH pH = log (1/ [H3O+]) = - log [H3O+] In a neutral solution, [H3O+] = [OH -] = 1.00 x 10 -7 at 25 oC at pH = -log (1.00 x 10 -7) = - (-7) = 7 BASIC This solution is _____________ because + [H3O +] < [OH --] 3 Kw = (x) (0.0010 + x) Because x << 0.0010 M, assume [OH-] = 0.0010 M [H3O+] = Kw / 0.0010 = 1.0 x 10 -11 M Page 1 + [H3O+], [OH--] and pH 3 7 + [H3O+], [OH--] and pH 3 8 Other pX Scales Scales In general and so Kw = [H3 [H O+] pX = -log X pOH = - log [OH -] [OH-] = 1.00 x 10-14 at 25 oC at 9 What is the pH of the 0.0010 M NaOH solution? [H3O+] = 1.0 x 10 -11 M pH = - log (1.0 x 10 -11) = 11.00 General conclusion — If the pH of Coke is 3.12, it is ____________. Because pH = - log [H 3O+] then log [H3O+] = - pH Take antilog and get Take the log of both sides -log (10-14) = - log [H3O+] + (-log [OH -]) Basic solution Basic Neutral Acidic solution pH > 7 pH = 7 pH < 7 [H3O+] = 10-pH [H3O +] = 10 -3.12 = 7.6 x 10 -4 M 7.6 14 = pH + pOH 14 Page 2 ...
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