S.4 Chemistry: Revision summary
Topic: Introduction of volumetric analysis & Experimental techniques in
volumetric analysis
● Volumetric analysis is a method used to determine the amount or
concentration of a substance by titration. It relies on the precise measurement
of volumes of solutions in chemical reactions.
● Acid-base titration is the process of gradually adding a solution (an acid/ an
alkali) from a burette into a known volume of another solution (an alkali/ an acid)
in a conical flask until two solutions completely react with each other.
Try to draw the titration set-up:
Common apparatus used in volumetric analysis:
Apparatus
Function
Pipette
It is used to transfer a specific volume of
solution accurately.
Pipette filler
It is used to fill a pipette with a solution.
Burette
It is used to deliver variable volume of a
solution accurately.
It is graduated so that one may record the
volume of solution added from the
burette.
Volume added = final reading - initial
reading
Volumetric flask
It is used to prepare a solution of a
specific volume.
Conical flask
It is used to hold a solution to be titrated.
Electronic balance
It is used to measure the mass of
chemicals accurately.
Exercise time
1. Choose the best suit apparatus for the following task:
(i) To weigh 2.56 g of a solid accurately
__electronic balance___
(ii) To deliver 25.0 cm3 of a solution accurately
_____pipette_________
(iii) To make up a 50 cm3 solution to 250.0cm3
___volumetric flask____
(iv) To hold or deliver a varied volume of solution
_____buirette________
(v) To measure about 23 cm3 solution
__measuring cylinder___
2. In an experiment, 25.0 cm3 of NaOH(aq) is measured with apparatus X and is placed
into apparatus Y is then titrated with a standard solution of HCl(aq) holding in apparatus
Z. State the name of apparatus X, Y and Z respectively.
Apparatus X: pipette
Apparatus Y: conical flask
Apparatus Z: burette
A. Experimental techniques of volumetric analysis
● Washing techniques of common apparatus in titration:
Apparatus
Washing steps
Pipette
Before use, rinse it with distilled water and then with the
solution it is going to transfer.
Burette
Before use, rinse it with distilled water and then with the
solution it is going to deliver.
Volumetric flask
Before use, rinse it with distilled water.
Conical flask
Before use, rinse it with distilled water.
●
Guiding Questions:
1. Suggest why the pipette is rinsed again with the solution it is going to contain after being
rinsed by distilled water.
To prevent the water remaining inside from diluting the solution sample.
2. Suggest why the burette is rinsed again with the solution it is going to contain after being
rinsed by distilled water.
To prevent the water remaining inside from diluting the solution sample transferred.
3. Suggest why the volumetric flask is ONLY rinsed by distilled water but not the solution it
is going to contain.
To prevent the addition of solution from increasing the number of moles of solution.
4. Suggest why the conical flask flask is ONLY rinsed by distilled water but not the solution
it is going to contain.
To prevent the addition of solution from increasing the number of moles of solution.
Note-taking on experimental techniques of volumetric analysis:
-
Always ensure pipette tip is inside the solution when getting the solution
-
No bubble in burette tips
-
Burette should be clamped vertically
-
Make sure to read the level of solution horizontally
-
The bottom of the meniscus would be the read to determine whether the graduation
mark is reached
-
Make sure to add few drops of indicator before starting titration
-
Use white tile to observe the colour change