Classical Method of Quantitative Analysis
Classical Method of Quantitative Analysis
Classical Method of Quantitative Analysis
Group: 11
Course Title: CLASSICAL METHOD OF QUANTITATIVE ANALYSIS
For this a known volume of sample solution is titrated against standard EDTA solution in the
presence of buffer solution of PH 10 using Eriochrome Black T as an indicator to find out the
volume of standard EDTA solution consumed to form Complex with Mg ++ as well as Ca++ present in
the sample solution.
In second, a known volume of sample solution is treated with 8M KOH solution to precipitate out
Mg++ as Mg(OH)2 and then the content is titrated against standard EDTA solution using Calcon as an
indicator to find out the volume of standard EDTA solution consumed to form Complex with Ca ++
present in sample solution.
Subtraction of volume of standard EDTA solution obtained in first step from the volume of standard
EDTA solution, consumed in second step corresponds to the volume of standard EDTA solution
consumed to form Complex with Mg++ present in sample solution.
INTRODUCTION OF CALCIUM:
Magnesium is the 4th most abundant mineral in the body and is essential to good health.
Approximately 50% of total Magnesium is found in bone, the other half is found inside
cells of body tissues and organs.
Only 1% of Magnesium is found in blood.
Sources Of Magnesium:
It is present in green vegetables such as spinach are good sources of Magnesium because
the centre of the chorophyll molecule contains Magnesium
Some regumes (beans and peas) nuts and seeds and whole unverfined are also good
sources of Magnesium
Uses Of Magnesium:
EDTA is a polyamino carboxylic acid and a colourless, water soluble solid. Its congugate
base is name ethylene diamine tetra acetate. It is widely used to dissolve lime scale.
MgSO4.7H2O
Eriochrome Black T is a complexometric indicator that is part of the complexometric titrations, e.g.
in the water hardness determination process. It is an azo dye.
In its protonated form, Eriochrome Black T is blue. It turns red when it forms a complex with
calcium, magnesium, or other metal ions.
How Eriochrome Black-T Works
When Eriochrome Black-T complexes with Mg2+ ions, it produces a PINK-RED solution. The
indicator is BLUE when the it is not complexed with Mg2+ (equation 2) and the solution is basic.
As EDTA is added to hard water during the titration it reacts with the divalent ions (e.g. Ca 2+ and
Mg2+) present in the hard water. Once all the divalent ions in solution have reacted with EDTA, the
EDTA reacts with the Mg2+ ions that are complexed with the Eriochrome Black-T indicator, thus
causing the solution to turn BLUE.
Equation 2. In-Mg(aq) In2-(aq) + Mg2+(aq)
Calcon Indicator
(a) All reactions between metal ions and EDTA are PH dependent and for divalent
ions, solutions must be kept basic (and buffered) for the reaction to go to completion.
(b) The erichrome Black T requires a PH of 8 - 10 for the desire colour change.
Chemical Equations:
Calculate the weight of MgSO4.7H2O to prepare its 0.01 M standard solution in 100 ml
volumetric flask.
Prepare 0.01 M standard MgSO4.7H2O solution in 100 ml volumetric flask.
Weight x (g) of MgSO4 .7H2O accurately in a vial, transfer to a volumetric flask, dissolve
in distilled water and make the volume of the solution upto the mark with distilled water.
Prepare about 250 ml of about 0.01 M disodium salt of EDTA solution in a beaker.
Weight about y (g) of Na2EDTA on watch glass transferred to a beaker, dissolve in
distilled water and the volume of the solution upto 250 ml with distilled water.
Rinse and fill the burette with Na2EDTA and remove air bubbles from the jet note initial
burette readings.
Transfer 10 ml of 0.01 M MgSO4.7H2O solution to a conical flask, add about 10 ml of
buffer solution of PH 10 and EBT to it and titrate the content of the conical flask against
NA2EDTA solution until red colour changes into blue. Note final burette reading.
Repeat the step until concordant readings obtained and calculate the molality of EDTA.
Analysis of Sample Solution:
1. A B C
2. B D C C
Volume of sample solution = 10 ml
Volume of KOH solution = about 5 ml about 8M
Indicator = Calcon
Volume of standard EDTA solution consumed:
1. H I J
2. J K J J
Analysis of sample solution:
Volume of sample solution = 10 ml
Volume of buffer solution of PH 10 = ml
Indicator = erichrome Black T
Volume of standard EDTA consumed:
S. No Initial reading Final reading Difference Concordant
(ml) (ml) (ml) reading
(ml)
1. D E F
2. E G F F
Calculations:
1 EDTA = 1 Ca++
Volume of standard Disodium Salt of EDTA solution consumed against Mg++ present in
Sample Solution = (Total Volume of Standard Disodium Salt of EDTA Solution
consumed against Ca++ and Mg++ present in sample solutio) - (Volume of Standard
Disodium Salt of EDTA Solution consumed against Ca++ Only present in Sample
Saolution.
Volume of Standard Disodium Salt of EDTA Solution consumed against Mg++ present
in Sample Solution
= (J - F)
= L ml
Determination of No. of mole of Mg present in 250ml ++
So, the No. of mole of Mg++ present in sample solution is s mol / 250ml
Determination of weight of Mg++ present in 250ml sample
solution ...
The No. of mole of Mg++ present in given sample solution is found to be s mol/250 ml
The weight of Mg++ present in the given sample solution is found to be T g/250ml
The No. of mol of Ca++ present in given sample solution is found to be p mol/250ml
The weight of Ca++ present in the given sample solution is found to be q g/250ml