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Ch.15: Acid-Base and pH Part 1. Self-Ionization of Water Pure water is a VERY weak electrolyte It undergoes self-ionization H 2 O (l) + H 2 O (l) H 3.

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Presentation on theme: "Ch.15: Acid-Base and pH Part 1. Self-Ionization of Water Pure water is a VERY weak electrolyte It undergoes self-ionization H 2 O (l) + H 2 O (l) H 3."— Presentation transcript:

1 Ch.15: Acid-Base and pH Part 1

2 Self-Ionization of Water Pure water is a VERY weak electrolyte It undergoes self-ionization H 2 O (l) + H 2 O (l) H 3 O + (aq) + OH - (aq) [H 3 O + ] means “hydronium ion concentration in moles per liter” In water, [H 3 O + ] = 1.0 x M and [OH - ] = 1.0 x M Ionization constant for water K w = 1.0 x

3 Neutral, Acidic, and Basic Solutions When [H 3 O + ] = [OH - ] the solution is neutral. When [H 3 O + ] is higher than the [OH - ], the solution is acidic. When the [OH - ] is higher than the [H 3 O + ], the solution is basic.

4 Calculating [H 3 O + ] and [OH - ] Remember, strong acids and bases are considered completely ionized in aqueous solutions. NaOH(s) H2O Na + (aq) + OH - (aq) 1 mol 1 mol 1 mol Therefore, whatever the molarity of the solution, that is the molarity of the ions produced.

5 [H 3 O + ] and [OH - ] determine pH and pOH Most often we express acidity and basicity in terms of pH or pOH. The pH of a solution is defined by the following equation: pH = - log [H 3 O + ] [H 3 O + ] = 10 -pH The pOH of a solution is defined by the following equation: pOH = - log [OH - ] [OH - ] = 10 -pOH Therefore: pH + pOH = 14

6 The pH Scale


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