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Bell Ringer Which of the following aqueous solutions will cause litmus paper to turn red? A NaOH B NaCl C HCl D H 2 O pH Solution Added Litmus paper changes from AcidNeutralBase Blue to Red Does not Change Red to Blue Source: 2003 VA EOC Exam

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pH Acids and Bases

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A Quick Reminder… Reactions can stop at an EQUILIBRIUM Image source: NO 2 + NO 2 N 2 O 4

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The Equilibrium Constant, K eq [C]c [D]d[C]c [D]d [A]a [B]b[A]a [B]b For the reaction: aA + bB cC + dD Where: a, b, c, d are coefficients A, B, C, D are substances (products) (reactants) [ ] = concentration in M K eq =

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The Equilibrium Constant, K eq For the reaction: NO 2 + NO 2 N 2 O 4 K eq = [N 2 O 4 ] 1 [NO 2 ] 1 K eq = [N 2 O 4 ] 1 [NO 2 ] 2 2 NO 2 N 2 O 4 = [N 2 O 4 ] [NO 2 ] 2 = [N 2 O 4 ] [NO 2 ] 2

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A Special Equilibrium Constant, K w For the reaction: H 2 O + H 2 O H 3 O + + OH - K w = [H 3 O + ] [OH - ] [H 2 O] 2 = [H 3 O + ] [OH - ] K w = [1.00 x ] = 1.00 x “hydronium”“hydroxide” Image source:

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Practice Problems Using the knowledge that K w = 1.00 x , solve for the missing piece of information: 1. Calculate the hydroxide ion concentration in a solution whose hydronium ion concentration is 1 x M K w = [H 3 O + ] [OH - ] 1.00 x = [1 x M] [OH - ] [OH - ] = 1.00 x x M = 1 x M

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Practice Problems 2. Calculate the hydronium concentration for a solution whose hydroxide concentration is M. K w = [H 3 O + ] [OH - ] 1.00 x = [H 3 O + ] [ M] [H 3 O + ] = 1.00 x M = 1 x M

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Practice Problems 3. What is the hydroxide concentration of a solution if grams of NaOH are dissolved in 2.0 L of solution? What is the hydronium ion concentration of this solution? g NaOH x 1 mol NaOH g NaOH x 1 mol OH - 1 mol NaOH = mol OH - [OH - ] = mol OH L = M OH - K w = [H 3 O + ] [OH - ] 1.00 x = [H 3 O + ] [ M] [H 3 O + ] = 1.00 x M =1.0 x M H 3 O +

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Practice Problems 4. What is the hydroxide ion concentration of a solution if grams of Ca(OH) 2 are dissolved in 2.0 L of solution? What is the hydronium ion concentration of this solution? g Ca(OH) 2 x 1 mol Ca(OH) g Ca(OH) 2 x 2 mol OH - 1 mol Ca(OH) 2 = mol OH - [OH - ] = mol OH L = M OH - K w = [H 3 O + ] [OH - ] 1.00 x = [H 3 O + ] [ M] [H 3 O + ] = 1.00 x M =9.3 x M H 3 O M OH x M H 3 O +

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pH – the POWER of H + ! These numbers represent the POWER of H + pH = the negative logarithm of [H 3 O + ] Image source:

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Log-o-rhythms == pH = the negative logarithm of [H 3 O + ]POWER pH – the POWER of H + ! Answer the following questions without using a calculator: What is the pH of a solution with [H 3 O + ] = 1.0 x M? pH = 4.00ACID What is the pH of a solution with [H 3 O + ] = 1.0 x M? pH = 12.00BASE pH = - log [H 3 O + ]

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My Kingdom for a Calculator! On TI-83: push “(-)” key push “log” key type in number On Scientific Calculators: type in number push “log” key push +/- key To solve for pH, given hydronium molarity

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Practice Problems 1. What is the pH of a solution if the concentration of hydronium ions is 1.0 x M? Is the solution acidic or basic? pH = - log [H 3 O + ] pH = - log (1.0 x ) pH = 2.00ACIDIC SIG FIG RULES: Put the correct number of Sig Figs BEHIND the decimal point.

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Practice Problems 2. What is the pH of a solution if the concentration of hydroxide ions is 1.0 x M? Is the solution acidic or basic? pH = - log [H 3 O + ] pH = - log (1.0 x ) pH = 10.00BASIC K w = [H 3 O + ] [OH - ] 1.00 x = [H 3 O + ] [1.0 x M] [H 3 O + ] = 1.00 x x M = 1 x M

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My Kingdom for a Calculator (again)! On TI-83: push “10 x ” key push “(-)” key type in pH On Scientific Calculators: type in number push +/- key push “2 nd ” key push “log” key To solve for hydronium molarity, given pH

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Practice Problems 3. What is the concentration of hydronium ions in a solution whose pH is 8.00? pH = 8.00 = - log [H 3 O + ] = log [H 3 O + ] 10 –8.00 M = [H 3 O + ] [H 3 O + ] = 1.00 x M

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Practice Problems 4. For Question #3, what is the concentration of hydroxide ions? K w = [H 3 O + ] [OH - ] 1.00 x = [1.0 x M] [OH - ] [OH - ] = 1.00 x x M = 1 x M

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Practice Problems 5. What is the concentration of hydronium ions in a solution that has a volume of 2.50 L and 5.33 g of HCl? What is the pH of this solution? 5.33 g HCl x 1 mol HCl g HCl x 1 mol H + 1 mol HCl = mol H + [H + ] =0.146 mol H L = M H + pH = - log [H 3 O + ] pH = - log (0.0584) pH = 1.234

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Homework Complete the practice problems on the worksheet. Due next class

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