What is pH?  Tells us the relative quantity of H+ ions (or the acidity) in solution.  The greater the [H+] the lower the pH. pH Values of Common Liquids H+ and OH- in Pure Water Self Ionization of Water: small quantity of water molecules in a sample will self ionize. Results in small, but equal [H+] and [OH-] Concentration of these ions is 1 x 10-7 M (pH = 7) Reversible reaction that is at equilibrium. H 2O H+ OH- http://youtu.be/kW-Zk4zABzw H+ + OH[H+] = [OH-] When Acid is Added to Water  Increases the H+ concentration  As H+ increases, OH- decreases [H+] > [OH-] H+ OH- When Base is Added to Water  Increases OH- concentration  When OH- increases, H+ decreases [OH] > [H+] H+ OH- pH Scale 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Basic Acidic Neutral [H+]>[OH-] [H+] = [OH-] [OH-]>[H+] Important Summary Acidic: [H+] > [OH-] Basic: [H+] < [OH-] Neutral: [H+] = [OH-] Pretty Hydrangeas  The color of hydrangea flowers depends on the pH of the soil. Calculating pH pH = - log [H+]  From the French pouvoir hydrogene (“hydrogen power” or power of hydrogen) [H+] pH 1 x 10-5 M 5 1 x 10-9 M 9 1 x 10-11 M 11 11  If the [H+] is 0.000001 M, what is the pH? pH = 6  If the [H+] is 0.01M, what is the pH? pH = 2  If the pH is 10, what is the [H+]? [H+] = 1 x 10-10 M  If the pH is 4, what is the [H+]? [H+] = 1 x 10-4 M Calculating pOH  What if you are given the concentration of a base?  Ex: .000001M LiOH You need to find the pOH!! pOH pOH = -log [OH-] Ex: .000001M LiOH = 1 x 10-6 pOH = 6 Ex: .0001M NaOH = 1 x 10-4 pOH = 4 How can you find pH of a Base?  Easy!!! pH + pOH = 14 Ex: .000001M LiOH = 1 x 10-6 pOH = 6 pH = 8 Ex: .0001M NaOH = 1 x 10-4 pOH = 4 pH = 10 Kw or Equilibrium Constant for Water If you know the concentration of one ion you can find the other! [H+] x [OH-] = 1 x 10-14  If [H+] is .001M what is the [OH-]? [1 x 10-3] x [OH-] = 1 x 10-14 [OH-] = 1 x 10-11 Everything keeps adding up to 14!! What’s up with that? Let’s Try It You have a .001 HCl solution. Find: [H+], [OH-], pH, pOH Let’s Try It You have a .000000001M NaOH solution. Find: [H+], [OH-], pH, pOH Equation Summary pH = -log [H+ ] [H+ ] = 10-pH pH + pOH = 14 pOH = -log [OH- ] [OH- ] = 10-pOH [H+ ] x [OH- ] = 1x10-14 Acidic solution: Neutral solution: Basic solution: pH < 7 pOH > 7 pH = 7 pOH = 7 pH > 7 pOH < 7 Let’s Practice  A solution with a pH of 2.0 has a hydronium ion concentration ten times greater than a solution with a pH of (1) 1 (2) 3 (3) 0.20 (4) 20  Which statement correctly describes a solution with a pH of 9? (1) It has a higher concentration of H3O+ than OH– and causes litmus to turn blue. (2) It has a higher concentration of OH– than H3O+ and causes litmus to turn blue. (3) It has a higher concentration of H3O+ than OH– and causes methyl orange to turn yellow. (4) It has a higher concentration of OH– than H3O+ and causes methyl orange to turn red.  What is the pH of a solution that has a hydronium ion concentration 100 times greater than a solution with a pH of 4? (1) 5 (2) 3 (3) 2 (4) 6  Solution A has a pH of 3 and solution Z has a pH of 6. How many times greater is the hydronium ion concentration in solution A than the hydronium ion concentration in solution Z? (1) 100 (2) 3 (3) 2 (4) 1000  When the pH of a solution changes from a pH of 5 to a pH of 3, the hydronium ion concentration is 1). 0.01 of the original content 2). 0.1 of the original content 3). 10 times the original content 4). 100 times the original content  As the pH of a solution is changed from 3 to 6, the concentration of hydronium ions (1) increases by a factor of 3 (2) increases by a factor of 1000 (3) decreases by a factor of 3 (4) decreases by a factor of 1000 Honors Questions If the pH of a solution is 3.25 find the pOH, [H+], and [OH-]. If .065 mole of KOH is placed in 20 liters of water, what is the resulting pH? Crash Course pH and pOH  http://www.youtube.com/watch?v=LS67vS 10O5Y&safe=active  Acid Rain (Not to be confused with “Chocolate Rain”) Acid Rain  Unpolluted rain has a pH of 5.6  It is naturally acidic due to the gases in the air that dissolve in it. Acid Rain  Rain with a pH below 5.6 is “acid rain“ pH of Rainwater across United States in 2001 Sources of Acid Rain Sources of Acid Rain  Power stations  Oil refineries  Coal with high S content  Car and truck emissions  Bacterial decomposition, and lightning hitting N2  CO2 in the air forms carbonic acid CO2 + H2O  H2CO3 This increases the [H+] of rain H2CO3 H+ (aq) + HCO3-(aq)  Reactions with oxygen in air form SO3 2SO2 + O2  2 SO3 Reactions with water in air form acids SO3 + H2O H2SO4 sulfuric acid NO + H2O HNO2 nitrous acid HNO2 + H2O HNO3 nitric acid Effects of Acid Rain Effects of Acid Rain  Leaches heavy metals like Al from soil, which kills fish  Fish kills in spring from runoff due to accumulation of large amounts of acid in snow  Prevents shellfish from building strong shells  Dissolves waxy coatings that protect leaves from bacteria  Corrodes metals, textiles, paper and leather Honors: pH and pOH game  http://www.quia.com/rr/4051.html  Acid Rain Destroys National Monuments http://news.discovery.com/videos/earth-acidrain-eating-washington-dc.html Global Warming: CO2 and Ocean Acidity http://planetgreen.discovery.com/videos/blue -august-acid-in-the-water.html Acid Rain Site produced by EPA  http://www.epa.gov/acidrain/education/site _kids/  EPA Website Detailing Acid Rain Causes and Effects as well as Legislation  http://www.epa.gov/acidrain/ 