[Science geek]

Could you please help me solve this problem
In  a 20 ml of solution zinc chloride concentration of 0,02 mol/dm3 a 15 ml solution of nickel(II) chloride of unknown concentration is added and the solution is diluted in a normal dish of 100 ml volume.For analysis 25 ml of that solution is taken.Then in that 25 ml solution 30 ml of EDTA solution of concetration of 0,0225 mol/dm3 is added. The formed solution is then titrated with standardized solution of magnesium sulfate of concentracion of 0,0505 mol/dm3 with the indicator eriochrome black T which requires a consumption of 5,10 ml of solution magnesium sulfate. Calculate the concentration of nickel (II) chloride.
Ka(ZnY2-)=3*10(16) alfay=0.052( pH=9) alfam=8*10(-6) (pH=9)

[Science geek]

It is similar to icho preparatory problem number 27

[Borek]

Wouldn't hurt to start writing reaction equations.

[Science geek]

Theseare reaction I know
MgSO4 + EDTA----> Mg(EDTA) + SO4
Zn2+ + Y4- ---------> ZNY2-
I am trying to solve this problem for several days but i can't
Here is a similar problem on icho
http://icho2015.msu.az/uploads/files/Preparatory_problems_IChO_2015_July_8.pdf       (here is the 27 problem )
http://icho2015.msu.az/uploads/files/Solutions_Preparatory_problems_IChO_2015_June_15.pdf (and here is the solution)
Can you help me solve this particular problem above

[Borek]

This is probably because you are making the problem harder than it really is. It is a simple back titration.

Do you know how the EDTA reacts with metals in general?

[Science geek]

EDTA4-+Mg2+--->[Mg-EDTA]2-

ErioT +Mg2+---->ErioT-Mg
Yes i know,but again i do not know what to do with all these informations, i Tried like this
CNi+= [VEDTA*CEDTA-VMgSO4*CMgSO4]/Valfa

alfaY=[ZnY2]/[EDTA]

Please can you explain this problem or do it step by step. I would be so grateful,please.

[Borek]

Looks to me like this information:

Ka(ZnY2-)=3*10(16) alfay=0.052( pH=9) alfam=8*10(-6) (pH=9)

is there just to confuse you. Ignore it.

Think in terms of a simple stoichiometry. Eriochrome black is just an indicator, its presence (nor the reaction with Mg²⁺) is not important for the titration result.

[Science geek]

I Must use all the informations that are given in the problem

[Borek]

Good luck then.

[Science geek]

Please somebody help me?

[Borek]

You have refused to even try to solve the problem following hints given. Nobody is going to solve the problem for you, especially when you are not showing any efforts.

[Science geek]

Can somebody just direct me what should I do?

[Science geek]

Should I ivolve relative activity constant KΘ