Titration curves and indicator theory

What are the 4 main types of titration curve?

* strong acid and strong base
* weak acid and strong base
* strong acid and weak base
* weak acid and weak base

Define end point

point at which the indicator changes colour (due to pH change)

Define equivalence point

volume at which titrant is chemically equivalent to the analyte

Where does the pH of the equivalence point lie on a titration curve?

the mid-point of the extrapolated vertical position of the curve

Where does neutralisation occur on a titration curve?

the steepest part of the curve

What is the pH of the equivalence point of a strong acid and strong base titration?

7

Between which pHs is the steepest part of a strong acid and strong base titration curve?

3 pH - 9 pH

What is the pH of the equivalence point of a weak acid and strong base titration?

>7 pH

Between which pHs is the steepest part of a weak acid and strong base titration curve?

7pH - 10pH

What is unique about the titration curve of a weak acid and strong base titration?

it has a buffer region → pH rises quickly at start and then flattens as buffer is made

What happens at half-neutralisation?

Ka = \[H+\]

pKa = pH

Between which pHs is the steepest part of a strong acid and weak base titration curve?

4 pH - 7 pH

What is the pH of the equivalence point of a strong acid and weak base titration?

What is the usual end-point of a weak acid and weak base titration and what can affect this?

* around 7 pH
* the relative strengths of the acid and the alkali

Why don’t weak acid and weak base titration curves have an equivalence point?

* behave as buffer solutions
* no dramatic pH change at end point → no steep part of curve

What is a polybasic acid?

an acid with more than one proton

How do polybasic acid and strong alkali titration curves differ from strong base and strong acid titration curves?

* reaction proceeds through more than one stage
* reactions don’t occur simultaneously → occur one at a time
* each stage has its own end point → reaction has as many end points as the number of protons in the acid

What are indicators?

acid or bases that can lose or gain protons

What is the equation for the dissociated of a protonated indicator?

HIn ⇌ In- + H+

What is the justification for the selection of a suitable indicator?

pH range of the indicator lies of the steepest part of the titration curve

What are indicators used for in acid-alkali titrations?

to find the end-point of a titration

Which titration curve is this?

weak acid and weak base

Which titration curve is this?

strong acid and weak base

Which titration curve is this?

weak acid and strong base

Which titration curve is this?

strong acid and strong base