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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 H2O pH 1-6 7 8-14 Solution Added Acid Neutral Base Litmus paper changes from 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 NO2 + NO2 N2O4**

Image source:

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**The Equilibrium Constant, Keq**

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

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**The Equilibrium Constant, Keq**

For the reaction: NO2 + NO N2O4 [N2O4]1 [N2O4] Keq = = [NO2]1 [NO2]1 [NO2]2 2 NO N2O4 [N2O4]1 [N2O4] Keq = = [NO2]2 [NO2]2

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**A Special Equilibrium Constant, Kw**

For the reaction: H2O H2O H3O OH- [H3O+] [OH-] [H3O+] [OH-] = Kw = [H2O]2 “hydronium” “hydroxide” [1.00 x 10-7] [1.00 x 10-7] = 1.00 x 10-14 Kw = Image source:

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Practice Problems Using the knowledge that Kw = 1.00 x 10-14, solve for the missing piece of information: 1. Calculate the hydroxide ion concentration in a solution whose hydronium ion concentration is 1 x 10-5 M Kw = [H3O+] [OH-] 1.00 x = [1 x 10-5 M] [OH-] [OH-] = x 10-14 = 1 x 10-9 M 1 x 10-5 M

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**Practice Problems Kw = [H3O+] [OH-] 1.00 x 10-14 = [H3O+] [0.0010 M]**

2. Calculate the hydronium concentration for a solution whose hydroxide concentration is M. Kw = [H3O+] [OH-] 1.00 x = [H3O+] [ M] [H3O+] = x 10-14 = 1 x M 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? M OH- 1.0 x M H3O+ 1 mol NaOH 1 mol OH- 0.080 g NaOH mol OH- x x = 40.00 g NaOH 1 mol NaOH [OH-] = mol OH- = M OH- 2.0 L Kw = [H3O+] [OH-] 1.00 x = [H3O+] [ M] [H3O+] = x 10-14 = 1.0 x M H3O+ M

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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? M OH- 9.3 x M H3O+ 1 mol Ca(OH)2 2 mol OH- 0.080 g Ca(OH)2 mol OH- x x = 74.10 g Ca(OH)2 1 mol Ca(OH)2 [OH-] = mol OH- = M OH- 2.0 L Kw = [H3O+] [OH-] 1.00 x = [H3O+] [ M] [H3O+] = x 10-14 = 9.3 x M H3O+ M

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**pH – the POWER of H+! pH = the negative logarithm of [H3O+]**

These numbers represent the POWER of H+ pH = the negative logarithm of [H3O+] Image source:

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**Log-o-rhythms Logarithm Exponent POWER = = pH – the POWER of H+!**

pH = the negative logarithm of [H3O+] POWER pH = - log [H3O+] Answer the following questions without using a calculator: What is the pH of a solution with [H3O+] = 1.0 x 10-4 M? pH = 4.00 ACID What is the pH of a solution with [H3O+] = 1.0 x M? pH = 12.00 BASE

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**My Kingdom for a Calculator!**

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

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**Practice Problems pH = - log [H3O+] pH = - log (1.0 x 10-2) pH = 2.00**

1. What is the pH of a solution if the concentration of hydronium ions is 1.0 x 10-2 M? Is the solution acidic or basic? pH = - log [H3O+] pH = - log (1.0 x 10-2) pH = ACIDIC SIG FIG RULES: Put the correct number of Sig Figs BEHIND the decimal point.

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**Practice Problems pH = - log [H3O+] pH = - log (1.0 x 10-10)**

2. What is the pH of a solution if the concentration of hydroxide ions is 1.0 x 10-4 M? Is the solution acidic or basic? Kw = [H3O+] [OH-] 1.00 x = [H3O+] [1.0 x 10-4 M] [H3O+] = x 10-14 = 1 x M 1.0 x 10-4 M pH = - log [H3O+] pH = - log (1.0 x 10-10) pH = BASIC

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**My Kingdom for a Calculator (again)!**

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

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**Practice Problems pH = 8.00 = - log [H3O+] -8.00 = log [H3O+]**

3. What is the concentration of hydronium ions in a solution whose pH is 8.00? pH = = - log [H3O+] = log [H3O+] 10–8.00 M = [H3O+] [H3O+] = x 10-8 M

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**Practice Problems Kw = [H3O+] [OH-]**

4. For Question #3, what is the concentration of hydroxide ions? Kw = [H3O+] [OH-] 1.00 x = [1.0 x 10-8 M] [OH-] [OH-] = x 10-14 = 1 x 10-6 M 1.0 x 10-8 M

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**Practice Problems pH = - log [H3O+] pH = - log (0.0584) pH = 1.234**

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? 1 mol HCl 1 mol H+ 5.33 g HCl 0.146 mol H+ x x = 36.46 g HCl 1 mol HCl [H+] = 0.146 mol H+ = M H+ 2.50 L pH = - log [H3O+] pH = - log (0.0584) pH =

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

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