Titration Curves

Question 1

How to find titrations curves?

Answer 1

Titrate the acid/alkali together: add 2cm3 in the burette
Measure pH using meter
Plot a graph to show variation

Question 2

Strong acid/strong base graph character

Answer 2

Straight line at very low acid pH then sharp increase which levels off to a straight line at very high pH
Vertical part = equivalence point when [H+] = [OH-]

Question 3

Vertical part on titration curve

Answer 3

All the [H+] has been neutralised as it equals the concentration of OH- so adding very small volumes of OH- rapidly increases the pH of the solution
Aka end point

Question 4

Strong acid weak base titration curve characteristics

Answer 4

Starts at very low strong acid pH
Smaller end point (vertical line) that does not level off at a very high pH because a weak base is being added (favours the bottom of the graph)

Question 5

Equivalence point in strong acid strong base

Answer 5

7

Question 6

Equivalence point in strong acid weak base

Answer 6

Under 7

Question 7

Weak acid/strong base curve characteristics

Answer 7

Not a very low acidic starting pH
Small end vertical point that levels off at a very high pH as a strong acid is used
Equivalence point is over 7

Question 8

Equivalence point of weak acid/strong base

Answer 8

Over 7

Question 9

What is formed when strong base is added to a weak acid?

Answer 9

A buffer region: resists change in pH as the strong base reacts with weak acid to form the weak acids salt
Which dissociates to form carboxylate ion: large concentration
So when more base is added, the position of equilibrium shifts so more of the weak acid dissociates to produce more H+ to neutralise added OH- (until too much added and no longer works)

Question 10

The volume at half the equivalence point

Answer 10

Is called the half neutralisation point because half of the acid has reacted with OH-
So half of weak acid is still remaining: half that does react is the weak acid’s salt formed

Question 11

The pH at the volume of the half neutralisation point is equal to…

Answer 11

pKa value
Because [HA] = [A-] So these cancel in Ka expression
Ka = [H+] and -log both sides
pKa = pH

Question 12

Weak acid weak base

Answer 12

Very small equivalence point starts at weak acid pH and ends at weak acid pH

Question 13

Indicators equilibrium equation

Answer 13

HIn <——> In- + H+

Question 14

When is a colour change seen in an indicator?

Answer 14

When [HIn] = [In-]
So we need an indicator which this point will coincide with the neutralisation point (vertical line) of the titration