Presentation on theme: "4.3 Volumetric analysis Learning outcomes"— Presentation transcript:
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 analysisA 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 solutionsA standard is a solution of precisely known concentrationIt must be available in a highly pure stateIt must be stable in airIt must dissolve easily in waterIt should have a fairly high relative molecular wtIt should under go a complete and rapid reaction
5 Non standard solutions Sodium hydroxide absorbs carbon dioxide from atmosphereHCl can produce chlorine gas in reactions and liberate hydrogen when exposed to airNitric acid can act as an oxidising agent interfering with reactionsSulphuric acid absorbs water form the air
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 PrecautionsConical flask should not be rinsed with solution it is to contain and swirlIn using a Volumetric flask the last few cm³ must be added so that the meniscus rest on calibration markInvert 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) RinsingTo 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 tapTo 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 exampleVolume of acid Va (cm3) is the titration figure from buretteThe concentration of acid is Ca (mol)na is the mol of full balanced equation per litreVolume of base is Vb (cm³ ). Usually placed in the conical flask.Cb is the concentration of the basena is the mol of full balanced per litre
23 Calculations USE FORMULA Va. Ca = Vb. Cb na nb Va = 37 cm³ Ca is unknownna = 2Vb = 25 cm³Cb = 0.1 molnb = 1
24 Va. Ca = Vb. Cbna nb37 cm³ × Ca = cm³ × 0.1molCa = 25 × 2 × = mol/L37
25 EXAM QUESTIONS Look out for dilution factors e.g vinegar Choice of indicatorType of vol flask given 1L OR 250 cm³ as you have to adjust in your calculationsTake titre reading from burette and given vol of solution is taken from conical flaskUSE FORMULA Va. Ca = Vb. Cbna nb