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### Topic: A complexed problem (solutions)  (Read 9625 times)

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#### Science geek

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##### A complexed problem (solutions)
« on: July 16, 2015, 05:41:19 PM »
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

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##### Re: A complexed problem (solutions)
« Reply #1 on: July 18, 2015, 02:53:38 AM »
It is similar to icho preparatory problem number 27

#### Borek

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##### Re: A complexed problem (solutions)
« Reply #2 on: July 18, 2015, 06:51:30 AM »
Wouldn't hurt to start writing reaction equations.
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#### Science geek

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##### Re: A complexed problem (solutions)
« Reply #3 on: July 18, 2015, 07:41:31 AM »
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

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##### Re: A complexed problem (solutions)
« Reply #4 on: July 18, 2015, 08:47:39 AM »
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?
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#### Science geek

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##### Re: A complexed problem (solutions)
« Reply #5 on: July 18, 2015, 09:00:23 AM »
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

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##### Re: A complexed problem (solutions)
« Reply #6 on: July 18, 2015, 12:23:02 PM »
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.
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#### Science geek

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##### Re: A complexed problem (solutions)
« Reply #7 on: July 18, 2015, 02:42:13 PM »
I Must use all the informations that are given in the problem

#### Borek

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##### Re: A complexed problem (solutions)
« Reply #8 on: July 18, 2015, 04:48:45 PM »
Good luck then.
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#### Science geek

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##### Re: A complexed problem (solutions)
« Reply #9 on: July 19, 2015, 02:44:57 AM »

#### Borek

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##### Re: A complexed problem (solutions)
« Reply #10 on: July 19, 2015, 03:24:10 AM »
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.
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#### Science geek

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##### Re: A complexed problem (solutions)
« Reply #11 on: July 23, 2015, 08:32:11 AM »
Can somebody just direct me what should I do?

#### Science geek

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##### Re: A complexed problem (solutions)
« Reply #12 on: July 23, 2015, 09:05:14 AM »
Should I ivolve relative activity constant KΘ