2. Acidic: [H3O+] > [OH-] Alkaline (basic): [OH-] > [H3O+]
Neutral: [OH-] = [H3O+]
Soren Sorensen developed a simplified system for the degree of acidity of a solution.
pH - the potenz (power) of hydrogen - German
potentia hydrogenii - Latin

3. Convenient and simple way to express [H+] Equation 1: pH = - log [H+]
Equation 2: [H3O+] = 10-pH
pOH has its own scale – like pH – that runs from 0-14 for strength of bases.
Equation 3: pOH = - log [OH-]
Equation 4: [OH-] = 10-pOH

4. Acidic - pH < 7 Basic - pH > 7
In a neutral solution pH & pOH = 7
Acidic - pH < 7
Basic - pH > 7
Equation 5: pH + pOH = 14

6. remember strong acids are 100% dissociating: [HA]i = [H+]e = [A-]e
1. Calculate the pH of an HCl solution whose concentration is 5.0 x 10-6 mol/L.
remember strong acids are 100% dissociating: [HA]i = [H+]e = [A-]e
pH = -log[H+]
= -log(5.0 x 10-6 M)
= -(-5.30)
= 5.30

7. Find the “10 x” button on your calculator.
2. The pH of a solution is Calculate the hydrogen ion concentration in the solution.
[H3O+] = 10-pH
Find the “10 x” button on your calculator. =
= 5.6 x 10-4 M

8. [OH-] = 10-pOH = 10-3.70 = 2.0 x 10-4 mol/L
3. The pH of a solution is 10.30, what is the hydroxide ion concentration?
OR solved this way
pOH = pH
pOH =
= 3.70
[H+] = 10-pH
[OH-] = KW
[H+]
[OH-] = 10-pOH =
= 2.0 x 10-4 mol/L

9. remember strong bases are 100% dissociating
4. What is the pH of 5.0 x 10-5 M Mg(OH)2 solution?
remember strong bases are 100% dissociating
Mg(OH)2 (s) Mg2+(aq) + 2 OH-(aq)
xi xf xf
[E]
[I]
[C]
- x
+ x
+ 2x x 2x
[OH-] = 2x = 2(5.0 x 10-5 M)
= 1.0 x 10-4 M
pOH = -log[OH-] = 4.00
pH = = 10.00

10. YOUR ACID/BASE FORMULAE:
Kw = [H+][OH-] = 1.0 x 10-14
The pH and pOH scales goes from
pH = -log[H+] and [H+] = 10-pH
pOH = -log[OH-] and [OH-] = 10-pOH
pOH + pH =14

11. Measuring pH Probe must be calibrated first.
There are two ways to measure pH:
pH Meters
Indicators
The [H+] inside the probe (reference electrode) is compared to [H+] outside the probe.
Probe must be calibrated first.
(inserted into known pH solution)

12. Indicator: a weak acid or base that undergoes a colour change when they gain or lose hydrogen ions.
Colour change occurs at various pH depending on indicator
Le Chatelier’s applies to the colour change
Natural pH indicators
Beets, Blackcurrant juice, Blueberries , Carrots , Cherries , Curry Powder , Grapes , Onion , Petunia Petals , Poison Primrose , Poppy Petals , Red cabbage , Red Radish , Rhubarb , Rose Petals , Strawberries ,Tea , Thyme , Turmeric , Tulip Petals , Violet Petals

14. Red Litmus stays red in the presence of an acid.

15. It turns blue in presense of a base.

16. Weak acid is colourless and its conjugate base ion is bright pink
Phenolphthalein is a commonly used indicator.
Weak acid is colourless and its conjugate base ion is bright pink

17. CAN YOU / HAVE YOU?
Formulate an operational definition of pH
Solve problems involving pH
Describe how an acid-base indicator works in terms of colour shifts and Le Chatelier’s Principle
Additional KEY Terms