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pH Chapter 19.3
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Vocabulary Word hydronium ion: H 3 O + hydroxide ion: OH -
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Ionization of Water When water ionizes it is acting as both an acid and a base in the same reaction H 2 O H + + OH - K eq =[H + ] [OH - ] [H 2 O]
![Ionization of Water When water ionizes it is acting as both an acid and a base in the same reaction H 2 O H + + OH - K eq =[H + ] [OH - ] [H 2 O]](http://images.slideplayer.com/22/6410537/slides/slide_3.jpg "Ionization of Water When water ionizes it is acting as both an acid and a base in the same reaction H 2 O H + + OH - K eq =[H + ] [OH - ] [H 2 O]")
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Ionization of Water K eq [H 2 O] = K w =[H + ] [OH - ] At 298K experimentally the K eq of water is 1.0 x 10 -14 K w = 1.0 x 10 -14 [H + ] = [OH - ] = 1.0 x 10 -7
![Ionization of Water K eq [H 2 O] = K w =[H + ] [OH - ] At 298K experimentally the K eq of water is 1.0 x K w = 1.0 x [H + ] = [OH - ] = 1.0 x 10 -7](http://images.slideplayer.com/22/6410537/slides/slide_4.jpg "Ionization of Water K eq [H 2 O] = K w =[H + ] [OH - ] At 298K experimentally the K eq of water is 1.0 x K w = 1.0 x [H + ] = [OH - ] = 1.0 x 10 -7")
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Using K w to Calculate [H + ] or [OH - ] If [H + ] = 1.0 x 10 -5, what is [OH-]? Kw = [H+] [OH-] 1.0 x 10 -14 = 1.0 x 10 -5 [OH-] 1.0 x 10 -14 = [OH-] 1.0 x 10 -5 [OH-] = 1.0 x 10 -9
![Using K w to Calculate [H + ] or [OH - ] If [H + ] = 1.0 x 10 -5, what is [OH-].](http://images.slideplayer.com/22/6410537/slides/slide_5.jpg "Kw = [H+] [OH-] 1.0 x = 1.0 x [OH-] 1.0 x = [OH-] 1.0 x [OH-] = 1.0 x")
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Acid or Base 1.0 x 10 -5 > 1.0 x 10 -9 [H+] >[OH-] Therefore the solution is an acid.
![Acid or Base 1.0 x > 1.0 x [H+] >[OH-] Therefore the solution is an acid.](http://images.slideplayer.com/22/6410537/slides/slide_6.jpg "Acid or Base 1.0 x > 1.0 x [H+] >[OH-] Therefore the solution is an acid.")
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pH Scale Since the concentrations of H+ and OH- are so small, chemists adapted a simpler way to express them on a log scale, pH. pH = - log [H+]
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Vocabulary Word pH = - log [H+], values range from 0 to 14. Acids have a pH less than 7. Bases have pH greater than 7.
![Vocabulary Word pH = - log [H+], values range from 0 to 14.](http://images.slideplayer.com/22/6410537/slides/slide_8.jpg "Acids have a pH less than 7. Bases have pH greater than 7..")
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Log Scales Since pH is measured on a log scale, each unit is a 10 fold change in [H+]. A difference in pH of 2 is a 100 fold change in [H+] A difference in pH of 5 units is a 100,000 change in [H+]
![Log Scales Since pH is measured on a log scale, each unit is a 10 fold change in [H+].](http://images.slideplayer.com/22/6410537/slides/slide_9.jpg "A difference in pH of 2 is a 100 fold change in [H+] A difference in pH of 5 units is a 100,000 change in [H+].")
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Calculating Acidity pH can also be calculated from the [H+] If [H+] = 1.0 x 10 -2 pH = - log 1.0 x 10 -2 = 2.0
![Calculating Acidity pH can also be calculated from the [H+] If [H+] = 1.0 x pH = - log 1.0 x = 2.0](http://images.slideplayer.com/22/6410537/slides/slide_10.jpg "Calculating Acidity pH can also be calculated from the [H+] If [H+] = 1.0 x pH = - log 1.0 x = 2.0")
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Calculating Basicity Sometimes chemists calculate basicity instead pOH is a measure of basicity pOH = - log [OH-]
![Calculating Basicity Sometimes chemists calculate basicity instead pOH is a measure of basicity pOH = - log [OH-]](http://images.slideplayer.com/22/6410537/slides/slide_11.jpg "Calculating Basicity Sometimes chemists calculate basicity instead pOH is a measure of basicity pOH = - log [OH-]")
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Vocabulary Word pOH: - log [OH-], values range from 0 to 14. Acids have a pOH of greater than 7 and bases have a pOH of less than 7.
![Vocabulary Word pOH: - log [OH-], values range from 0 to 14.](http://images.slideplayer.com/22/6410537/slides/slide_12.jpg "Acids have a pOH of greater than 7 and bases have a pOH of less than 7..")
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Calculating pH or pOH pH + pOH = 14 If [OH-] = 4.0 x 10 -3, calculate the pH and the pOH. given [OH-], so pOH = - log 4.0 x 10 -3 pOH = 2.4 pH = 14 - 2.4 = 11.6
![Calculating pH or pOH pH + pOH = 14 If [OH-] = 4.0 x 10 -3, calculate the pH and the pOH.](http://images.slideplayer.com/22/6410537/slides/slide_13.jpg "given [OH-], so pOH = - log 4.0 x pOH = 2.4 pH = =")
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Calculating [H+] or [OH-] If the pH of a solution is 3.5, calculate [H+] and [OH-] given pH, so 3.5 = - log [H+] [H+] = antilog -3.5 [H+] = 3.2 x 10 -4
![Calculating [H+] or [OH-] If the pH of a solution is 3.5, calculate [H+] and [OH-] given pH, so 3.5 = - log [H+] [H+] = antilog -3.5 [H+] = 3.2 x 10 -4](http://images.slideplayer.com/22/6410537/slides/slide_14.jpg "Calculating [H+] or [OH-] If the pH of a solution is 3.5, calculate [H+] and [OH-] given pH, so 3.5 = - log [H+] [H+] = antilog -3.5 [H+] = 3.2 x 10 -4")
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Calculating [H+] or [OH-] If pH = 3.5, pOH = 14 - 3.5 = 10.5 pOH = - log [OH-] 10.5 = - log [OH-] antilog -10.5 = [OH-] [OH-] = 3.16 x 10 -11
![Calculating [H+] or [OH-] If pH = 3.5, pOH = = 10.5 pOH = - log [OH-] 10.5 = - log [OH-] antilog = [OH-] [OH-] = 3.16 x](http://images.slideplayer.com/22/6410537/slides/slide_15.jpg "Calculating [H+] or [OH-] If pH = 3.5, pOH = = 10.5 pOH = - log [OH-] 10.5 = - log [OH-] antilog = [OH-] [OH-] = 3.16 x")
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Measuring pH Litmus can distinguish acids from bases –acids turn litmus red –bases turn litmus blue A quantitative value of pH can be measured using: –indicator paper (pH paper) –a pH meter
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