VolumetricVolumetric analysisanalysisA 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 solutionsStandard solutions

A standard is a solution of precisely known A standard is a solution of precisely known concentration concentration

It must be available in a highly pure stateIt must be available in a highly pure state It must be stable in airIt must be stable in air It must dissolve easily in waterIt must dissolve easily in water It should have a fairly high relative It should have a fairly high relative

molecular wtmolecular wt It should under go a complete and rapid It should under go a complete and rapid

reactionreaction

Non standard solutionsNon standard solutions

Sodium hydroxide absorbs carbon Sodium hydroxide absorbs carbon dioxide from atmospheredioxide from atmosphere

HCl can produce chlorine gas in HCl can produce chlorine gas in reactions and liberate hydrogen reactions and liberate hydrogen when exposed to airwhen exposed to air

Nitric acid can act as an oxidising Nitric acid can act as an oxidising agent interfering with reactionsagent interfering with reactions

Sulphuric acid absorbs water form Sulphuric acid absorbs water form the airthe air

Na2CO3 + 2HCl 2NaCl + H2O + CO2

1 mole 2 moles 2 moles 1 mole 1 mole

EQUIPMENEQUIPMENTT

Apparatus usedApparatus used

BuretteBurette Volumetric flask Volumetric flask BeakerBeaker PipettePipette FunnelFunnel IndicatorIndicator White tileWhite tile

Burette titration procedures

Precautions when using Precautions when using equipmentequipment

Burette must be vertical, use and then Burette must be vertical, use and then remove funnel, check meniscus, rinse remove funnel, check meniscus, rinse with de-ionised water and then given with de-ionised water and then given solution.solution.

In using a Pipette rinse with de-ionised In using a Pipette rinse with de-ionised water first and then with given water first and then with given solution. Check meniscus. Do not blow solution. Check meniscus. Do not blow out remainder of liquid into flask and out remainder of liquid into flask and keep tip of pipette in contact with flaskkeep tip of pipette in contact with flask

PrecautionsPrecautions

Conical flask should not be rinsed Conical flask should not be rinsed with solution it is to contain and swirl with solution it is to contain and swirl

In using a Volumetric flask the last In using a Volumetric flask the last few cmfew cm³ must be added so that the ³ must be added so that the meniscus rest on calibration markmeniscus rest on calibration mark

Invert stoppered flask to ensure Invert stoppered flask to ensure solution is homogeneous/uniformsolution is homogeneous/uniform

Why is a conical flask, rather Why is a conical flask, rather than a beaker, used in the than a beaker, used in the

experiment?experiment?

To allow easy mixing of the contents, To allow easy mixing of the contents, by swirling.by swirling.

Why is the funnel removed Why is the funnel removed from the burette after from the burette after

adding the acid solution?adding the acid solution?

So that drops of solution from the So that drops of solution from the funnel will not fall into the burette.funnel will not fall into the burette.

In using a burette, why is it In using a burette, why is it important important

(a) to rinse it with a (a) to rinse it with a little of the solution it is little of the solution it is

going to contain. going to contain. (b) to clamp it (b) to clamp it

vertically. (c) to have vertically. (c) to have the part below the tap the part below the tap

full?full?

Solution (a) RinsingSolution (a) Rinsing

To remove any residual water, and To remove any residual water, and so avoid dilution of the acid solution so avoid dilution of the acid solution when it is poured into the burette.when it is poured into the burette.

Solution (b) clamp verticallySolution (b) clamp vertically

To enable the liquid level to be To enable the liquid level to be read correctlyread correctly

Solution (c) Full tapSolution (c) Full tap

To ensure that the actual volume of To ensure that the actual volume of liquid delivered into the conical liquid delivered into the conical flask is read accurately.flask is read accurately.

The following procedures were The following procedures were carried out carried out duringduring the the

titration:titration: The sides of the conical flask The sides of the conical flask

were washed down with were washed down with deionised water.deionised water.

The conical flask was The conical flask was frequently swirled or shaken.frequently swirled or shaken. Give one reason for carrying Give one reason for carrying out each of these procedures.out each of these procedures.

To ensure that all of the To ensure that all of the acid added from the acid added from the burette can react with burette can react with the base.the base.

To ensure complete To ensure complete mixing of the reactantsmixing of the reactants

Why is a rough titration carried out?Why is a rough titration carried out?

To find the approximate end-point. To find the approximate end-point. This information enables the This information enables the subsequent titrations to be carried subsequent titrations to be carried out more quickly.out more quickly.

Why is more than one accurate Why is more than one accurate titration carried out?titration carried out?

To minimise error by getting To minimise error by getting accurate readings within 0.1 cm3 of accurate readings within 0.1 cm3 of each other.each other.

CalculationsCalculations

Volume of acid Volume of acid Va Va (cm(cm33)) is the is the titration figure titration figure from burettefrom burette

The concentration The concentration of acid is of acid is Ca (mol)Ca (mol)

na na is the mol of full is the mol of full balanced equation balanced equation per litreper litre

Volume of base is Volume of base is Vb Vb (cm(cm33). Usually ). Usually placed in the placed in the conical flask.conical flask.

CbCb is the is the concentration of concentration of the basethe base

nana is the mol of full is the mol of full balanced per litrebalanced per litre

CalculationsCalculations

USE FORMULA USE FORMULA VVa. Ca a. Ca = = Vb. CbVb. Cb nna nba nb Va = 37cmVa = 37cm33

Ca is unknownCa is unknown na = 2na = 2 Vb = 25 cmVb = 25 cm33

Cb = 0.1 molCb = 0.1 mol nb = 1nb = 1

37 cm3× Ca = 25cm3 × 0.1mol

2 1

Ca = 25 × 2 × 0.1 = 0.13 mol/L

37

VVa. Ca a. Ca = = Vb. CbVb. Cb na na nb nb

EXAM QUESTIONSEXAM QUESTIONS

Look out for dilution factors e.g vinegarLook out for dilution factors e.g vinegar Choice of indicatorChoice of indicator Type of vol flask given 1L OR 250 CmType of vol flask given 1L OR 250 Cm³ as ³ as

you have to adjust in your calculationsyou have to adjust in your calculations Take titre reading from burette and given Take titre reading from burette and given

vol of solution is taken from conical flaskvol of solution is taken from conical flask USE FORMULA USE FORMULA VVa. Ca a. Ca = = Vb. CbVb. Cb nna nba nb