Hello Raju,
The proposed method uses oxalate to precipitate the calcium present as insoluble calcium oxalate, and titrate the dissolved Mg+2 ion with EDTA. The indicator normally used for this titration is Eriochrome Black T, which has a colour change at the endpoint from wine red to pure blue. Since this colour change may be difficult for some people to see clearly, the procedure often states something like;- "When you think it is blue, read the buret, then add another drop of EDTA titrant; if there is a perceptible color change, again read the buret and add another drop. Continue until a drop of EDTA gives no color change, then record the preceding buret reading." Soluble iron interferes and should be complexed with KCN.
The titrated amount of magnesium in the sample (expressed as as MgO), is calculated as follows;-
Weight of sample = 0.5000g
Volume of final solution = 500ml
Volume of aliquot taken for titration = 50ml
Molarity of EDTA solution = 0.002M
Volume of EDTA used in titration = Vmls
Since 1 mole EDTA reacts with 1mole Mg+2 which is equivalent to 1mole MgO
Then;-
Moles of MgO in 50ml aliquot = V/1000 * 0.002
Moles of MgO in 500ml = V/1000 * 0.002 * 10
gms of MgO in 500ml = V/1000 * 0.002 * 10 * 40.3
Since the MgO contained in the 500ml originated from the 0.5g sample;-
gms of MgO in 0.5g sample = V/1000 * 0.002 * 10 * 40.3
%MgO in sample = (V/1000 * 0.002 * 10 * 40.3) / 0.5 * 100
= V * 0.1612
If different weights of sample and molarities of EDTA are used, then for a final solution volume of 500ml and a 50ml sample aliquot, the calculation formula becomes;-
%MgO in sample = (V * M) / W * 40.3
Where;-
V = Volume of EDTA used in titration (mls)
M = molarity of EDTA solution used. (M)
W = weight of sample taken (gms)
Regards,
Ted.
thank you ted
regards
raju verma
Dear Sir
You are very warm Hearted as you welcome all the questions very politely.
I'm immensely thankful to you.
Ravi Chauhan
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Thank you Ravi,
It's my pleasure to be of help.
Regards,
Ted.