Slide 1

Acidity, Basicity, and pH

Slide 2

Water is both an acid and a base. We call this __________________. By the Br nsted-Lowry definition, this means that water can donate a proton AND accept a proton. H 2 O (l) + H 2 O (l) H 3 O + (aq) + OH - (aq) This process is known as the self-ionization of water.

Slide 3

The self-ionization of water makes even pure water have ions within it. In pure water, the two ions (acidic and basic) must share the same concentration (1:1 ratio) Experiments show that this concentration is 1.00x10 -7 M at 25C. [H 3 O + ] = [OH - ] = 1.00x10 -7 M

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Slide 5

The equilibrium constant is an expression that relates the concentrations of species involved in an equilibrium. To write an equilibrium constant expression, you must know the concentrations of the products and the reactants at equilibrium. K eq = [Products] / [Reactants] **Excluding solids and liquids

Slide 6

Consider the equilibrium of water: H 2 O (l) + H 2 O (l) H 3 O + (aq) + OH - (aq) 2H 2 O (l) H 3 O + (aq) + OH - (aq) This equations Equilibrium Constant is: K eq = (1.00x10 -7 )(1.00x10 -7 ) = 1.00x10 -14 This is a special equilibrium constant, known as K w

Slide 7

K eq = (1.00x10 -7 )(1.00x10 -7 ) = 1.00x10 -14 This is the Self-Ionization Constant of Water Known as K w We can use this information about water and the relationship of hydronium and hydroxide to figure out various concentrations in solutions [H 3 O + ][OH - ] = K w = 1.00x10 -14

Slide 8

What is [OH - ] in a 3.00x10 -5 M solution of HCl? 1.HCl = a strong acid or a strong base? I.So, is this a hydroxide conc or a hydronium conc? II.Since this is a strong acid it completely ______________, implying that [HCl] = [H 3 O + ] 2.Remember the self-ionization constant of water I.K w = [H 3 O + ][OH - ] = 1.00x10 -14 3.Plug in your variables and calculate what your are asked to find.

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What is [OH - ] in a 3.00x10 -5 M solution of HCl? K w = [H 3 O + ][OH - ] = 1.00x10 -14 1.00x10 -14 = (3.00x10 -5 M)[OH - ] 1.00x10 -14 = [OH - ] 3.00x10 -5 M [OH - ] = 3.33x10 -10 M

Slide 10

A solution is neutral when the concentration of hydroxide is exactly equal to the concentration of the hydronium. pH = 7 If the conc of the hydronium is stronger than the conc of the hydroxide than the solution with have a pH of 7.

Slide 11

The pH is a value used to express the acidity or alkalinity of a solution; it is defined as the logarithm of the reciprocal of the concentration of hydronium ions. p = power,H = hydrogen pH = power of hydrogen pH = -log[H 3 O + ] [H 3 O + ] = 10 -pH

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pH is a logarithmic scale, meaning an increase in a value is an increase of 10x i.e. A solution whose pH is 2.0 has a [H 3 O+] that is 10x greater than a solution whose pH is 3.0 and a 100x greater than a solution whose pH is 4.0

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What is the pH of the following solutions: 0.00010 M solution of HNO 3 ? 0.0136 M solution of KOH?

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What are the concentrations of the hydronium and hydroxide ions in a sample of rain that has a pH of 5.05? Gather info: pH = 5.05 K w = 1.00x10 -14 [H 3 O + ] = ? [OH - ] = ? Plan your work

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Method #1 Uses indicators Quick and simple Does not, however, give very precise results Method #2 Uses a pH meter Very precise More complicated and expensive

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Certain dyes with change different colors in solutions of different pH These dyes are known as indicators. A compound that can reversibly change color depending on the pH of the solution or other chemical change. The color after the addition of the indicator can help determine the relative pH of the solution.

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Litmus is a dye used as an indicator that is soaked into filter paper It serves as a quick, cheap, convenient check of a solutions pH. Blue Litmus Paper Turns red under acidic conditions Red Litmus Paper Turns blue under basic conditions

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pH meters are a probe that is submerged into a solution. An electrical voltage develops between two electrodes and the probe digitally reads out a pH value. The voltage is a measure of the conductivity of the hydronium solution.

Slide 19

Page 547, # 1, 2, 5, 6, 7, 8, 9, 10 Due tomorrow!! Vocab also due on Wednesday.