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1. 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

2. pH Ms. Besal 4/14/2006

3. A Quick Reminder… • Reactions can stop at an EQUILIBRIUM NO2 + NO2 N2O4 Image source: http://cwx.prenhall.com

4. aA + bBcC + dD (products) (reactants) The Equilibrium Constant, Keq For the reaction: • Where: • a, b, c, d are coefficients • A, B, C, D are substances [C]c[D]d Keq = [A]a[B]b [ ] = concentration in M

5. NO2 + NO2 N2O4 2 NO2 N2O4 The Equilibrium Constant, Keq For the reaction: [N2O4]1 [N2O4] Keq = = [NO2]1 [NO2]1 [NO2]2 [N2O4]1 [N2O4] Keq = = [NO2]2 [NO2]2

6. H2O + H2O H3O+ + OH- A Special Equilibrium Constant, Kw For the reaction: [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: http://cwx.prenhall.com

7. 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 10-14 = [1 x 10-5 M] [OH-] [OH-] = 1.00 x 10-14 = 1 x 10-9 M 1 x 10-5 M

8. Practice Problems 2. Calculate the hydronium concentration for a solution whose hydroxide concentration is 0.0010 M. Kw = [H3O+] [OH-] 1.00 x 10-14 = [H3O+] [0.0010 M] [H3O+] = 1.00 x 10-14 = 1 x 10-11 M 0.0010M

9. Practice Problems 3. What is the hydroxide concentration of a solution if 0.080 grams of NaOH are dissolved in 2.0 L of solution? What is the hydronium ion concentration of this solution? 0.0010 M OH- 1.0 x 10-11 M H3O+ 1 mol NaOH 1 mol OH- 0.080 g NaOH 0.0020 mol OH- x x = 40.00 g NaOH 1 mol NaOH [OH-] = 0.0020 mol OH- = 0.0010 M OH- 2.0 L Kw = [H3O+] [OH-] 1.00 x 10-14 = [H3O+] [0.0010 M] [H3O+] = 1.00 x 10-14 = 1.0 x 10-11 M H3O+ 0.0010M

10. Practice Problems 4. What is the hydroxide ion concentration of a solution if 0.080 grams of Ca(OH)2 are dissolved in 2.0 L of solution? What is the hydronium ion concentration of this solution? 0.0020 M OH- 9.3 x 10-12 M H3O+ 1 mol Ca(OH)2 2 mol OH- 0.080 g Ca(OH)2 0.00216 mol OH- x x = 74.10 g Ca(OH)2 1 mol Ca(OH)2 [OH-] = 0.00216 mol OH- = 0.00108 M OH- 2.0 L Kw = [H3O+] [OH-] 1.00 x 10-14 = [H3O+] [0.00108 M] [H3O+] = 1.00 x 10-14 = 9.3 x 10-12 M H3O+ 0.00108M

11. pH – the POWER of H+! These numbers represent the POWER of H+ pH = the negative logarithm of [H3O+] Image source: http://www.lowimpactdevelopment.org

12. 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 10-12 M? pH = 12.00 BASE

13. 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

14. Practice Problems 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 = 2.00 ACIDIC SIG FIG RULES: Put the correct number of Sig Figs BEHIND the decimal point.

15. Practice Problems 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 10-14 = [H3O+] [1.0 x 10-4 M] [H3O+] = 1.00 x 10-14 = 1 x 10-10 M 1.0 x 10-4 M pH = - log [H3O+] pH = - log (1.0 x 10-10) pH = 10.00 BASIC

16. 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

17. Practice Problems 3. What is the concentration of hydronium ions in a solution whose pH is 8.00? pH = 8.00 = - log [H3O+] -8.00 = log [H3O+] 10–8.00 M = [H3O+] [H3O+] = 1.00 x 10-8 M

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

19. 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? 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+ = 0.0584 M H+ 2.50 L pH = - log [H3O+] pH = - log (0.0584) pH = 1.234