Performing a Titration & Volumetric Analysis

Question 1

The key piece of equipment used in the titration is the burette
Burettes are usually marked to a precision of 0.10 cm3
Since they are analogue instruments, the uncertainty is recorded to

Answer 1

half the smallest marking, in other words to ±0.05 cm3

Question 2

The end point or equivalence point occurs when

Answer 2

the two solutions have reacted completely and is shown with the use of an indicator

Question 3

A white tile is placed under the conical flask while the titration is performed, to make it easier to see

Answer 3

colour change

Question 4

The steps in a titration are: step 1

Measuring a known volume (usually 20 or 25 cm3) of one of the solutions with a volumetric pipette and placing it into a ………..

Answer 4

conical flask

Question 5

The other solution is placed in the burette
To start with, the burette will usually be filled to

Answer 5

0.00 cm3

Question 6

A few drops of the indicator are added to the solution in the

Answer 6

conical flask

Question 7

The tap on the burette is carefully opened and the solution added, portion by portion, to the conical flask until the ………………

Answer 7

indicator starts to change colour

Question 8

As you start getting near to the end point, the flow of the burette should be slowed right down so that the solution is added

Answer 8

dropwise

Question 9

You should be able to close the tap on the burette after one drop has caused the colour change
Multiple runs are carried out until

Answer 9

concordant results are obtained
Concordant results are within 0.1 cm3 of each other

Question 10

Recording and processing titration results
Both the initial and final burette readings should be recorded and shown to a precision of ±0.05 cm3, the same as the uncertainty

Question 11

The volume delivered (titre) is calculated and recorded to an uncertainty of ±0.10 cm3
The uncertainty is doubled, because

Answer 11

two burette readings are made to obtain the titre (V final – V initial), following the rules for propagation of uncertainties
Concordant results are then averaged, and non-concordant results are discarded
The appropriate calculations are then done

Question 12

Percentage uncertainties are a way to compare the significance of an absolute uncertainty on a measurement

This is not to be confused with percentage error, which is a comparison of a result to a literature value

The formula for calculating percentage uncertainty is as follows

Answer 12

percentage uncertainty = uncertainty / measured value x 100%

Question 13

When you are adding or subtracting two measurements then you add together the absolute measurement uncertainties
For example,

Using a balance to measure the initial and final mass of a container

Using a thermometer for the measurement of the temperature at the start and the end

Using a burette to find the initial reading and final reading

In all these example you have to read the instrument twice to obtain the quantity

If each you time you read the instrument the measurement is ‘out’ by the stated uncertainty, then your final quantity is potentially ‘out’ by twice the uncertainty