Acid-Base Acid-Base Titration Titration and pHand pH

Self-Ionization of WaterSelf-Ionization of Water

H2O + H2O H3O+ + OH-

Though pure water is considered a non-conductor, there is a slight, but measurable conductivity due to “self-ionization”

Ion Concentration in Ion Concentration in SolutionsSolutions

KKww – Ionization Constant for – Ionization Constant for WaterWater

In pure water at 25 C:

[H3O+] = 1 x 10-7 mol/L

[OH-] = 1 x 10-7 mol/L

Kw is a constant at 25 C:

Kw = [H3O+][OH-]

Kw = (1 x 10-7)(1 x 10-7) = 1 x 10-

14

H+, OH-, and pHH+, OH-, and pH

pH pH ScalScal

ee

Calculating pH, Calculating pH, pOHpOHpH = -log10(H3O+)

pOH = -log10(OH-)

Relationship between pH and Relationship between pH and pOHpOH pH + pOH = 14

Finding [HFinding [H33OO++], [OH], [OH--] from pH, pOH] from pH, pOH

[H3O+] = 10-pH

[OH-] = 10-pOH

pH CalculationspH Calculations

H + O H -

pH pO H

[O H -] = 1 x 10 - 1 4

[H + ]

[H + ] = 1 x 10 - 1 4

[O H -]

p O H = 14 - p H

p H = 14 - p O H

pOH

= -l

og[O

H- ]

pH =

-log

[H+

]

[OH

- ] = 1

0-pO

H

[H+

] = 1

0-pH

Measuring pH with wide-range Measuring pH with wide-range paperpaper

Narrow-Range pH PaperNarrow-Range pH Paper

pH pH IndicatorIndicator

s s and theirand theirrangesranges

Some Acid-Base IndicatorsSome Acid-Base Indicators

IndicatorIndicator pH Range in whichpH Range in whichColor Change OccursColor Change Occurs

Color ChangeColor Changeas pH Increasesas pH Increases

Crystal violetCrystal violetThymol blueThymol blueOrange IVOrange IVMethyl orangeMethyl orangeBromcresol Bromcresol greengreenMethyl redMethyl redChlorophenol Chlorophenol redredBromthymol Bromthymol bluebluePhenol redPhenol redNeutral redNeutral redThymol blueThymol bluePhenolphthaleinPhenolphthaleinThymolphthaleinThymolphthaleinAlizarin yellowAlizarin yellowIndigo carmine Indigo carmine

0.0 - 1.60.0 - 1.61.2 - 2.81.2 - 2.81.4 - 2.81.4 - 2.83.2 - 4.43.2 - 4.43.8 - 5.43.8 - 5.44.8 - 6.24.8 - 6.25.2 - 6.85.2 - 6.86.0 - 7.66.0 - 7.66.6 - 8.06.6 - 8.06.8 - 8.06.8 - 8.08.0 - 9.68.0 - 9.6

8.2 - 10.08.2 - 10.09.4 - 10.69.4 - 10.610.1 - 12.010.1 - 12.011.4 - 13.0 11.4 - 13.0

yellowyellow to to blueblueredred to to yellowyellowredred to to yellowyellowredred to to yellowyellowyellowyellow to to blueblueredred to to yellowyellowyellowyellow to to redredyellowyellow to to blueblueyellowyellow to to redredredred to to amberamberyellowyellow to to bluebluecolorless to colorless to pinkpinkcolorless to colorless to blueblueyellowyellow to to blueblueblueblue to to yellowyellow

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0.00 5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.00 45.00m illiliters NaOH (0.10 M)

pH

Weak Acid/Strong Base Weak Acid/Strong Base TitrationTitration

A solution that is 0.10 M CH3COOH is titrated with 0.10 M NaOH

Endpoint is above pH 7

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0.00 5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.00 45.00

m illiliters NaOH (0.10 M)

pH

Strong Acid/Strong Base Strong Acid/Strong Base TitrationTitration

A solution that is 0.10 M HCl is titrated with 0.10 M NaOH

Endpoint is at pH 7

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0.00 5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.00 45.00

m illiliters HCl (0.10 M)

pH

Strong Acid/Strong Base Strong Acid/Strong Base TitrationTitration

A solution that is 0.10 M NaOH is titrated with 0.10 M HCl

Endpoint is at pH 7 It is important to

recognize that titration curves are not always increasing from left to right.

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0.00 5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.00 45.00

m illiliters NH3 (0.10 M)

pH

Strong Acid/Weak Base Strong Acid/Weak Base TitrationTitration

A solution that is 0.10 M HCl is titrated with 0.10 M NH3

Endpoint is below pH 7