1. 4.3 Volumetric analysis Learning outcomes
To understand the apparatus used in volumetric analysis and correct titrimetric procedure.

2. Students should know the following key words:
Volumetric analysis,titration,standard and non standard solutions

3. Volumetric analysis
A titration is a lab procedure where a measured volume of one solution (burette) is added to a known volume (flask) of another solution until the reaction is complete

4. Standard solutions
A standard is a solution of precisely known concentration
It must be available in a highly pure state
It must be stable in air
It must dissolve easily in water
It should have a fairly high relative molecular wt
It should under go a complete and rapid reaction

5. Non standard solutions
Sodium hydroxide absorbs carbon dioxide from atmosphere
HCl can produce chlorine gas in reactions and liberate hydrogen when exposed to air
Nitric acid can act as an oxidising agent interfering with reactions
Sulphuric acid absorbs water form the air

6. 1 mole 2 moles 2 moles 1 mole 1 mole
Sodium Carbonate and Hydrochloric acid
Na2CO HCl  2NaCl H2O CO2
1 mole moles moles mole mole

7. EQUIPMENT

8. Apparatus used Burette Volumetric flask Beaker Pipette Funnel
Indicator
White tile

9. Burette titration procedures

10. Precautions when using equipment
Burette must be vertical, use and then remove funnel, check meniscus, rinse with de-ionised water and then given solution.
In using a Pipette rinse with de-ionised water first and then with given solution. Check meniscus. Do not blow out remainder of liquid into flask and keep tip of pipette in contact with flask

11. Precautions
Conical flask should not be rinsed with solution it is to contain and swirl
In using a Volumetric flask the last few cm³ must be added so that the meniscus rest on calibration mark
Invert stoppered flask to ensure solution is homogeneous/uniform

12. Why is a conical flask, rather than a beaker, used in the experiment?
To allow easy mixing of the contents, by swirling.

13. Why is the funnel removed from the burette after adding the acid solution?
So that drops of solution from the funnel will not fall into the burette.

14. In using a burette, why is it important (a) to rinse it with a little of the solution it is going to contain. (b) to clamp it vertically. (c) to have the part below the tap full?

15. Solution (a) Rinsing
To remove any residual water, and so avoid dilution of the acid solution when it is poured into the burette.

16. Solution (b) clamp vertically
To enable the liquid level to be read correctly

17. Solution (c) Full tap
To ensure that the actual volume of liquid delivered into the conical flask is read accurately.

18. The following procedures were carried out during the titration: The sides of the conical flask were washed down with deionised water. The conical flask was frequently swirled or shaken. Give one reason for carrying out each of these procedures.

19. To ensure that all of the acid added from the burette can react with the base.
To ensure complete mixing of the reactants

20. Why is a rough titration carried out?
To find the approximate end-point. This information enables the subsequent titrations to be carried out more quickly.

21. Why is more than one accurate titration carried out?
To minimise error by getting accurate readings within 0.1 cm³ of each other.

22. Calculation example
Volume of acid Va (cm3) is the titration figure from burette
The concentration of acid is Ca (mol)
na is the mol of full balanced equation per litre
Volume of base is Vb (cm³ ). Usually placed in the conical flask.
Cb is the concentration of the base
na is the mol of full balanced per litre

23. Calculations USE FORMULA Va. Ca = Vb. Cb na nb Va = 37 cm³
Ca is unknown
na = 2
Vb = 25 cm³
Cb = 0.1 mol
nb = 1

24. Va. Ca = Vb. Cb
na nb
37 cm³ × Ca = cm³ × 0.1mol
Ca = 25 × 2 × = mol/L 37

25. EXAM QUESTIONS Look out for dilution factors e.g vinegar
Choice of indicator
Type of vol flask given 1L OR 250 cm³ as you have to adjust in your calculations
Take titre reading from burette and given vol of solution is taken from conical flask
USE FORMULA Va. Ca = Vb. Cb
na nb