Acidity, Basicity, and pH

 Water is both an acid and a base. We call this __________________.  By the Br Ø 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.

 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 25°C. [H 3 O + ] = [OH - ] = 1.00x10 -7 M

 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

 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 equation’s Equilibrium Constant is: K eq = (1.00x10 -7 )(1.00x10 -7 ) = 1.00x  This is a special equilibrium constant, known as K w

 K eq = (1.00x10 -7 )(1.00x10 -7 ) = 1.00x  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

 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 - ] = 1.00x Plug in your variables and calculate what your are asked to find.

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

 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.  If the conc of the hydroxide is stronger than the conc of the hydronium than the solution with have a pH of >7.

 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

 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

 What is the pH of the following solutions: ◦ M solution of HNO 3 ? ◦ M solution of KOH?

 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 = 1.00x [H 3 O + ] = ? [OH - ] = ?  Plan your work

 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

 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.

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

 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.

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