Astudent added 25.0 ul of a solution of magnesium chloride to a microcentrifuge tube along with a color changing indicator, and titrated with 1.00 x 10−2 m edta to the endpoint. the color change occurred at 21.3 ul. what was the [mg2+]?

Mg^2+ + EDTA^4-   ->   MgETDA^2-

 

number µmoles of EDTA used = 21.3 µl x 1 x 10^-2 M = 21.3 µl x 1 x 10^-2 µm/µl = 21.3 x 10^-2 = 0.213 µmoles EDTA

 

µmoles Mg^+2 present = 0.213 µmoles because the stoichiometry ratio of the above equation is 1:1

 

[Mg^+2] = 0.213 µmol / 25 µl = 0.00852 µmol/µl = 0.00852 M = 8.52 x 10^-3 M

The answer is 8.52 x 10^-3 M

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