Indicators

Substances that change color to signal the end of a titration.

Indicators

Substances that change color to signal the end of a titration.the end point ≠ the equivalence point.

Indicators

Substances that change color to signal the end of a titration.the end point ≠ the equivalence point

When chosen properly, the endpoint and equivalence point occur simultaneously (within experimental error).

Indicators are weak acids or weak bases.

HIn (aq) ⇌ H+ (aq) + In− (aq)

color 1 color 2

Indicators are weak acids or weak bases.

HIn (aq) ⇌ H+ (aq) + In− (aq)

color 1 color 2

Bromthymol blue

HIn (acid) form In− (base) form

The color observed for the indicator during an acid-base titration depends on the ratio[HIn]

[¿¿¿−]¿

The indicator color change is visible over a pH range given approximately by indicator pKIn ± 1.

KIn = 1.0 x 10−7, pKIn = 7

Useful pH range is 7 ± 1

Bromthymol blue

The indicator color change is visible over a pH range given approximately by indicator pKIn ± 1.

KIn = 1.0 x 10−7, pKIn = 7

Useful pH range is 7 ± 1 At or below a pH of 6 the indicator is yellow.

Bromthymol blue

The indicator color change is visible over a pH range given approximately by indicator pKIn ± 1.

KIn = 1.0 x 10−7, pKIn = 7

Useful pH range is 7 ± 1 At or below a pH of 6 the indicator is yellow.At pH 7 it is pale green.

Bromthymol blue

The indicator color change is visible over a pH range given approximately by indicator pKIn ± 1.

KIn = 1.0 x 10−7, pKIn = 7

Useful pH range is 7 ± 1 At or below a pH of 6 the indicator is yellow.At pH 7 it is pale green.At pH 8 and above, the color is blue.

Bromthymol blue

Always choose an indicator that changes color at or slightly after the equivalence point.

Always choose an indicator that changes color at or slightly after the equivalence point.

The titration of 0.100 M HCl with 0.100 M NaOH.

The titration of a weak base, NH3, by a strong acid, HCl.

Titration of a polyprotic acid.