NOTES: 19.2 – Hydrogen Ions & Acidity (pH and pOH)

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Hydrogen Ions and Acidity

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Presentation transcript:

NOTES: 19.2 – Hydrogen Ions & Acidity (pH and pOH)

pH scale:

Ionization of water ● Experiments have shown that pure water ionizes very slightly: H 2 O + H 2 O  H 3 O + + OH - ● Measurements show that in pure water: [H 3 O + ] = [OH - ] = 1 x M ● Pure water contains equal concentrations of H 3 O + and OH -, so it is NEUTRAL.

What is pH? ● pH is a measure of the concentration of hydronium ions in a solution. ● pH = -log [H 3 O + ] or ● pH = -log [H + ]

Example: What is the pH of a solution where [H 3 O + ] = 1 x M? pH = -log [H 3 O + ] pH = -log(1 x ) pH = 7

Example: What is the pH of a solution where [H 3 O + ] = 1 x M? pH = -log [H 3 O + ] pH = -log(1 x ) pH = 5 **When acid is added to water, the [H 3 O + ] increases, and the pH DECREASES.

Example: What is the pH of a solution where [H 3 O + ] = 1 x M? pH = -log [H 3 O + ] pH = -log(1 x ) pH = 10 **When a base is added to water, the [H 3 O + ] decreases, and the pH INCREASES.

The pH Scale Acid Neutral Base

What is pOH? ● pOH is a measure of the concentration of hydroxide ions (OH - ) in a solution. ● pOH = -log [OH - ]

Example: What is the pOH of a solution where [OH - ] = 1 x M? pOH = -log [OH - ] pOH = -log(1 x ) pOH = 5

How are pH and pOH related? ● At every pH, the following relationships hold true: [H 3 O + ] [OH - ] = 1 x M pH + pOH = 14

Example 1 : What is the pH of a solution where [H + ] = 3.4 x M? pH = -log [H + ] pH = -log(3.4 x M) pH = 4.5

Example 2 : What is the pOH of a solution where [OH - ] = 6.23 x M? pOH = -log [OH - ] pOH = -log (6.23 x M) pOH = 7.21

Example 3: The pH of a solution is measured to be What is the [H + ] in this solution? pH = -log [H + ] 8.86 = -log [H + ] = log [H + ] [H + ] = antilog (-8.86) [H + ] = [H + ] = 1.38 x M

Example 4: The pH of a solution is measured to be What is the [OH - ] in this solution? pH + pOH = 14, so pOH = 14 – 1.65 = pOH = -log [OH - ] = -log [OH - ] = log [OH - ] [OH - ] = antilog (-12.35) [OH - ] = [OH - ] = x M

Example 5: What is the pH of a solution where [H + ] = 5.4 x M? pH = -log [H + ] pH = -log(5.4 x ) pH = 5.3

Example 6: What is the [OH - ] and pOH for the solution in example #5? [H 3 O + ][OH - ]= 1 x (5.4 x )[OH - ] = 1 x [OH - ] = 1.9 x M pOH = -log(1.9 x ) pOH = 8.7

Example 7: What is the pOH of a solution where [OH - ] = 1.47 x M? pOH = -log [OH - ] pOH = -log( 1.47 x ) pOH = 3.83

Example 8: What is the [H + ] and pH for the solution in example #7? [H 3 O + ][OH - ]= 1 x [H 3 O + ](1.47 x ) = 1 x [H 3 O + ] = 6.80 x M pH = -log(6.80 x ) pH = 10.2