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Calculating pH and pOH Notes

Calculating pH and pOH Notes. Objectives. Calculate pH or pOH from [H + ] or [OH - ] Calculate [H + ] or [OH - ] from pH or pOH. What is pH?. The pH of a solution is a way to express the hydrogen ion concentration [H + ] in a solution Remember that the pH scale ranges from 0-14

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Calculating pH and pOH Notes

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  1. Calculating pH and pOH Notes

  2. Objectives • Calculate pH or pOH from [H+] or [OH-] • Calculate [H+] or [OH-] from pH or pOH

  3. What is pH? • The pH of a solution is a way to express the hydrogen ion concentration [H+]in a solution • Remember that the pH scale ranges from 0-14 • A pH of 0 is strongly acidic • A pH of 14 isstrongly basic • A pH of 7 is neutral

  4. Calculating pH and pOH • While pH tells you the concentration of hydrogen ions [H+] in a solution, the pOHtells you the concentration of hydroxide ions [OH-] in a solution. • The sum of pOH and pH should always be 14 pH + pOH = 14

  5. Calculating pH • To calculate pH: pH = -log[H+] • Sample Problem: What is the pH of a solution with a hydrogen ion concentration of 3.2 x 10-3M • pH = 2.5

  6. Calculating pOH • To calculate pOH pOH = -log[OH-] • Sample Problem: What is the pOH of a solution with a hydroxide ion concentration of 1.8 x 10-14M • pOH = 13.7

  7. Sample Problems • Calculate the pH or pOH from the following information • pH = 6.00 pOH = 14-6 = 8 • pH = 12.25 pOH = 14-12.25 = 1.75 • pOH = 3.10 pH = 14-3.10 = 10.9 • pOH = 10.45 pH = 14-10.45 = 3.55

  8. Sample Problems • Calculate the pH andpOH of the following concentrations: • [OH-] = 3.0 x 10-2 M • pOH = log(3.0 x 10-2 M) = 1.5 • [H+]= 6.0 x 10-10 M • pH = log(6.0 x 10-10 M) = 9.22 • [OH-] = 1.0 x 10-7 M • pOH = log(1.0 x 10-7 M) = 7 • [H+] = 2.0 x 10-7 M • pH = log(2.0 x 10-7 M) = 6.7

  9. Calculating [H+] • To calculate [H+] you must know the pH of the solution • The negative pHcan then be plugged into the antilog function(10^x) on your calculator [H+] = 10^-pH • The pH of unknown solution is 6.35. What is its hydrogen ion concentration? [H+] = 10^-6.35 =4.5 x 10-7

  10. Calculating [OH-] • To calculate [OH-] you must know thepOHof the solution • The negative pOHcan then be plugged into the antilog function (10^x) on your calculator [OH-] = 10^-pOH • The pOH of a solution is 3.42. What is its hydroxide ion concentration? [OH-] = 10^-3.42 =3.8 x 10-4

  11. Why Measure pH? • Plant growth • Chemical levels in swimming pools • Medical diagnoses

  12. Sample Problems • Calculate the [H+] or [OH-] from the following information. • pOH = 9.76 • [OH-] = 10^-9.76 =1.7 x 10-10 • pOH = 2.86 • [OH-] = 10^-2.86 =1.4 x 10-3 • pH = 13.07 • [H+] = 10^-13.07 =8.5 x 10-14

  13. pOH = 5.77 • [OH-] = 10^-5.77 =1.7 x 10-6 • pH = 1.98 • [H+] = 10^-1.98 =1.0 x 10-2 • pH = 10.25 • [H+] = 10^-10.25 =5.6 x 10-11

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