Homework Help: Chemistry

Posted by Lauren--PLEASE HELP on Sunday, November 29, 2009 at 1:47pm.

Analysis of Tap water (Hardness)

Was analyzed by a complexometric titraion by the following equations 1 & 2

1. Ca^2+ + Mg^2+ --> Ca^2+ + Mg(Indicator)

2. Mg(Indicator) + Ca^2+ + EDTA^4- --> CaEDTA^2- + MgEDTA^2- + free indicator

For the volume of titrant used (9.95 mL) calculate the:

a) Ca^2+ + Mg^2+ in sample (mol)
b)[Ca^2+] + [Mg^2+] of sample (M)

PLEASE HELP! I am very confused with this question and any guidance would be greatly appreciated!!!

Chemistry - DrBob222, Sunday, November 29, 2009 at 1:51pm
I am confused by the question also. Is this a problem to be solved or is it a procedure that you have summarized with the two equations? I may be able to help if I know the procedure followed. The complexometric titration with EDTA is usually straight forward.
Chemistry - Lauren--PLEASE HELP, Sunday, November 29, 2009 at 2:32pm
The equations 1 & 2 were given, and I believe we are supposed to make an equation for the reaction from this i.e. add them so that:

Ca^2+ + Mg^2+ + EDTA --> MgEDTS^2- + CaEDTA-

So by using the given volume of titrant (EDTA=9.95 mL) we could find the mol of Ca and Mg...i'm just not sure how to go about doing this (the stoichiometry is confusing me since the concentration they are looking for is Ca and Mg added...)

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