Published on Feb 21, 2020
Aim is To Determine Percentage Purity of a Given Iron Wire
Volumetric analysis is a mode of determining the quantity of a substance present in given solution by allowing a definite amount of it to react quantitatively with a solution of another substance of known concentration. The main process of this analysis is called titration.
Some definitions are:
o End Point: The point in the titration at which the reaction involved in it is just complete.
o Indicator: Substance used in titration to mark the completion of the reaction by distinct colours.
o Titrand: The solution which is to be titrated.
o Titrant: The solution of known strength.
o Strength of solution: The amount of a substance present in definite volume of the solution.
o Molarity: Number of moles of solute present, per litre of the solution is called its molarity.
Some apparatus used are:
o Measuring flask: It is flat-bottomed flask with a long narrow neck and fitted with an airtight glass stopper in its mouth.
o Burette: It is used for delivering definite volume of a solution into the titration flask. It is a long graduated cylindrical glass tube with a uniform cross-section.
o Pipette: It is used for accurate measurements of a definite volume of solution. It is a narrow glass tube with a bulb in the middle and a jet at its lower end
A substance can be taken as primary standard if it possess the following properties:
1. Should be easily available in a state of high purity.
2. Should not be deliquescent.
3. Should not be readily soluble in water.
4. Its solution should be stable during storage.
A reaction involving simultaneous oxidation and reduction reaction is termed as a redox reaction. Electrons are transferred from the substance getting oxidised to the substance getting reduced.
Here Fe3+ is reduced to Fe2+ and Sn2+ is oxidised to Sn4+ .
In titration, the reducing agent is titrated against a standard oxidising agent or vice or versa.
The loss of one or more electrons by an atom or an ion is termed as oxidation. e.g; change of oxalate ion to CO2
The gain of one or more electrons by an atom or an ion is termed as Reduction
Here, permanganate ion gains 5 electrons and changes to mangenous ions.
Equivalent mass of an oxidising agent=>
It is the ratio of molecular mass of the substance to the total number of electrons gained by 1 mole of substance during the reaction.
Equivalent mass of KMnO4:
(in acidic medium) = 158/5 = 31.6 gm
Equivalent mass of an redusing agent=>
It is the ratio of the molecular mass of the Substance to the total number of electrons lost by 1 mole of substance during the reaction.
e.g. Equivalent mass of an oxalate ion is 88/2g = 44gm.
Preparation of standard solution of oxalic acid containing gm. Of oxalic acid:
a) 0.126gm of oxalic acid was weighed in a beam balance and transferred into a 100ml measuring cylinder using a funnel. Oxalic acid sticking to the sides of funnel was washed with distilled water and then solution was made to 100 ml.
b) Measuring cylinder was shaken well and oxalic acid solution of 0.01M was obtained.
2. Preparation of 1M sulphuric acid solution from 18M sulphuric acid solution :
a) A little amount was distilled water was taken in a 250ml measuring cylinder.13.9ml of 18M H2SO4 was poured into measuring cylinder drop by drop and allowed it to cool for some time before resuming with addition of distilled water.
b) After all the sulphuric acid has been added to the solution it was made up to the 250ml mark by adding distilled water. A sulphuric acid solution of approx. 1M was obtained.
3. Preparation of ferrous sulphate solution
a) dissolved in conc. H2SO4 as it weighed approx. 3.10 gm.
b) After sometime iron nail was weighed again and was found to be 2.51 gm.
c) Then it was dissolved in 1M H2SO4 solution to make FeSO4 solution in a separate flask.
4. Filtration of impurities from ferrous sulphate solution and dilution of filtrate:
a) The above solution was filtered into a 250 ml measuring cylinder using funnel on which a filter paper was kept to hold the impurities.
b) The 150 ml filtrate was then diluted to 250 ml volume by adding distilled water through funnel.
5. Preparation of 0.026M potassium permanganate solution:
a) 0.316 gm of potassium permanganate was weighed in a beam balance and transferred into a 100ml measuring cylinder using a funnel. Distilled water was then added till the level of solution reached 100ml mark.
b) A potassium permanganate solution of approx. 0.02M was obtained.
6. Titration for standardisation of KMnO4 solution:
The KMnO4 solution was standardised using 0.01M oxalic acid solution and exact molarity of KMnO4 was determined.
7. Determination of percentage purity of iron wire:
a) 10 ml of ferrous sulphate solution was pipetted out in a flask already rinsed with the solution and titrated against standard KMnO4 solution till concordant readings were obtained.
b) The percentage of iron was then calculated using the above information