Simplest Formula - Shows pH pOH pKw and calculationsd

1. Simplest Formula Series in Chemistry
Power of the Hydrogen Ion
Stephen Joseph Boylan
February 2018
Course Learning Outcome: Calculate pH, pOH, pKw, [H+], [OH-], Kw values from
sufficient initial data

3. Power of the
Hydrogen Ion
Stephen Joseph Boylan
February 2018

4. Definitions
The power of the hydrogen ion is pH
The power of the hydroxide ion is pOH

5. Definitions
pH = - log [H+]
pOH = - log[OH-]
Log = logarithm to base 10

6. Case 1 Pure Water in a Closed Container

7. Case 1 Model of Pure Water
Ionization very very small
H2O  H+ (aq) + OH- (aq)
Molarity of water = 55 moles H2O per Liter
Molarity of Hydrogen Ion 25 C = 1.0 x 10^-7 moles per liter
Molarity of Hydroxide Ion 25 C = 1.0 x 10^-7 moles per liter

8. Case 1 Model of Pure Water
At Equilibrium
H2O  H+ (aq) + OH- (aq)
Kw = [H+]x[OH-] pKw = - log Kw

9. Case 1 Model of Pure Water
At Equilibrium and 25 C
Kw = [H+]x[OH-]
Kw = 1.0 x 10^-14 pKw = 14.0

10. Case 1 Model of Pure Water
At Equilibrium and 25 C
Kw = [H+]x[OH-]
Kw = 1.0 x 10^-14

11. Case 1 Model of Pure Water
pH = - log (1.0 x 10^-7 moles H+ per liter)
pH = 7.00
pOH = - log ( 1.0 x 10^-7 moles OH- per liter)
pOH = 7.00

12. Case 2 Strong Acid in Water

13. Case 2 Add hydrochloric acid to water
•Add 0.01 mole of hydrochloric acid to water
•Final volume of solution is 1 liter

14. Case 2 Model of Strong Acid
•Ionization 100%
•HCl => H+ (aq) + Cl- (aq)
•Molarity of Hydrogen Ion = 0.01 moles per liter
•Molarity of Chloride Ion = 0.01 moles per liter

15. Case 2 Calculate the pH of the strong acid
•Equation: pH = - log [H+]
•Substitute values: pH = - log (0.01)
•Calculate pH = 2.0000000…
•Round to answer: pH = 2.00

16. Case 2 Hydrochloric Acid in Water with pH meter

17. Case 2 Calculate hydrogen ion
concentration from pH
•Measure the pH with a pH meter
•The pH meter reads 1.57

18. Case 2 Calculate the molarity of hydrogen ion
•Equation: [H+] = 10 ^ (- pH)
•Substitute values: [H+] = 10 ^ (- 1.57)
•Calculate: [H+] = 0.026915348
•Round number to answer: [H+] = 0.027
•Show units: [H+] = 0.027 moles H+ per liter

19. Case 2 Calculate the molarity of hydroxide ion
•Assume 25 C Kw = 1.0x10^-14 = [H+][OH-]
•Solve for [OH-]: [OH-] = Kw / [H+]
•substitute values: [OH-] = 1.0x10^-14 / 0.027
•Calculate: [OH+] = 3.7037…x10^-13
•Round number:[OH+] = 3.7x10^-13
•Show units: 3.7x10^-13 moles hydroxide per liter

20. Object Oriented Analysis
•6 Variables
•pH, [H+], pOH, [OH-], Kw, pKw
•4 relations
•2 degrees of freedom
•Many simple algorithms

21. Summary
•Calculate pH from [H+]
•Calculate [H+] from pH
•Many other calculations

22. Equations from Equilibrium
H2O  H+ (aq) + OH- (aq)
Kw = [H+]x[OH-] pKw = - log Kw
At 25 C Kw = 1.0 x 10^(-14.0)
At 25 C pH + pOH = 14.0

23. Equations from Definitions
pH = - log [H+]
[H+] = 10 ^ (- pH)
pOH = - log [OH-]
[OH-] = 10 ^ (- pOH)

24. Thank You for Watching

25. The End
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