Volumetric analysis : 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 Standard solutions : 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 Non standard solutions : 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 Slide 4: Na2CO3 + 2HCl 2NaCl + H2O + CO2
1 mole 2 moles 2 moles 1 mole 1 mole Slide 5: EQUIPMENT Apparatus used : Apparatus used Burette
White tile Slide 7: Burette titration procedures Precautions when using equipment : 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 Precautions : 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 Why is a conical flask, rather than a beaker, used in the experiment? : Why is a conical flask, rather than a beaker, used in the experiment? To allow easy mixing of the contents, by swirling. Why is the funnel removed from the burette after adding the acid solution? : 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. 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? : 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? Solution (a) Rinsing : Solution (a) Rinsing To remove any residual water, and so avoid dilution of the acid solution when it is poured into the burette. Solution (b) clamp vertically : Solution (b) clamp vertically To enable the liquid level to be read correctly Solution (c) Full tap : Solution (c) Full tap To ensure that the actual volume of liquid delivered into the conical flask is read accurately. 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. : 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. Slide 17: To ensure that all of the acid added from the burette can react with the base.
To ensure complete mixing of the reactants Slide 18: 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. Slide 19: Why is more than one accurate titration carried out?
To minimise error by getting accurate readings within 0.1 cm3 of each other. Calculations : Calculations 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 Calculations : Calculations USE FORMULA Va. Ca = Vb. Cb
Va = 37cm3
Ca is unknown
na = 2
Vb = 25 cm3
Cb = 0.1 mol
nb = 1 Slide 22: 37 cm3× Ca = 25cm3 × 0.1mol
Ca = 25 × 2 × 0.1 = 0.13 mol/L
37 Va. Ca = Vb. Cb
na nb EXAM QUESTIONS : 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