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Hydrogen Ions and Acidity Chapter 19.2. What is K w ? K w is the equilibrium constant for the self-ionization of water Water molecules are in constant.

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Presentation on theme: "Hydrogen Ions and Acidity Chapter 19.2. What is K w ? K w is the equilibrium constant for the self-ionization of water Water molecules are in constant."— Presentation transcript:

1 Hydrogen Ions and Acidity Chapter 19.2

2 What is K w ? K w is the equilibrium constant for the self-ionization of water Water molecules are in constant motion and can collide to create a hydronium ion and a hydroxide ion

3 Where does K w come from? 2H 2 O (l) H 3 O + (aq) + OH - (aq) K w = [H + ][OH - ] __________ [H 2 O] 2 K w = [H + ][OH - ] But we remove liquids and solids

4 Self Ionization Concentration Ion-Product Constant Called the self-ionization of water [H + ] = [OH - ] = 1.0 x M The ion-product constant for water (K w ) K w = [H + ][OH - ] = 1.0 x M 2 Neutral solution [H + ]=[OH - ] Acidic solution [H + ] > [OH - ] Basic solution [H + ] < [OH - ]

5 pH Scale and Formulas pH is an easier way to express the strengths of acids and bases pH scale ranges from considered acidic RED 7 considered neutral 8-14 considered basic BLUE pH = -log [H + ] [H + ] = antilog(pH) pOH = -log [OH - ] [OH-] = antilog(pOH) pH + pOH = 14 [H + ][OH - ] = 1.0 x

6 Practice Problems What is the pH of a substance that has an [H + ] concentration of 1 x ? What about 1 x ? What is the pH of a substance that has an [H + ] concentration of 6.27 x ? 4.0; 5.0; 4.2

7 Practice Problems What is the [H + ] concentration of a substance that has a pH of 8.00? What is the [OH - ] concentration? What is the [H + ] concentration of a substance that has a pH of 8.73? What is the [OH - ] concentration? What is the pOH? 1 x ;1 x ;1.86 x ;5.39 x ; 5.27


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