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Ch.15: Acid-Base and pH

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 O + ( aq ) + OH - ( aq ) [H 3 O + ] means “ hydronium ion concentration in moles per liter”

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Ch.15: Acid-Base and pH

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  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 H2O (l) + H2O (l) H3O+(aq) + OH-(aq) • [H3O+] means “hydronium ion concentration in moles per liter” • In water, [H3O+] = 1.0 x 10-7 M and [OH-] = 1.0 x 10-7 M • Ionization constant for water Kw= 1.0 x 10-14

  3. Neutral, Acidic, and Basic Solutions • When [H3O+] = [OH-] the solution is neutral. • When [H3O+] is higher than the [OH-], the solution is acidic. • When the [OH-] is higher than the [H3O+], the solution is basic.

  4. Calculating [H3O+] and [OH-] • Remember, strong acids and bases are considered completely ionized in aqueous solutions. NaOH(s) H2ONa+(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. [H3O+] 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 [H3O+] [H3O+] = 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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