[freddy]

Hi guys,

I'm new to the forums and would really appreciate your kindly assistance. I'm trying as hard as i can to answer problems but i often encounter some difficulties. I'm struggling with EDTA calculations if someone can please help me.

q1) A 50.0 mL sample containing Ni2+ was reacted with 25.00 mL of 0.0500 M EDTA to complex all the Ni2+ and leave excess EDTA in solution. 5.00 mL of 0.0500 M Zn2+ was required to react with the excess EDTA. What was the concentration of Ni2+ in the original solution?

q2)Sulfide ion (S2-) was determined by indirect titration with EDTA. To a solution containing 25.00 mL 0.04332 M Cu(ClO4)2 and 15 mL 1 M pH 4.5 acetate buffer was added 25.00 mL of unknown S2- solution, with vigorous stirring. The CuS precipitate was filtered off and washed with hot water. Ammonia solution was then added to the filtrate (which now contains excess Cu2+) until the blue colour of Cu(NH3)42+ was observed. Murexide indicator was then added and the solution required 12.11 mL 0.03927 M EDTA to reach the end point. Determine the [S2-]?

Can you please show working out.

Thankyou i appreciate the help

[Borek]

First, write reaction equations. These are relatively simple stoichiometric calculations, as long as you don't have reaction equations and you don't know what is happening in the solutions you won't be able to calculate anything.

These may help, but reaction equations are a must:

http://www.titrations.info/titration-calculation

http://www.titrations.info/back-titration

[freddy]

Thanks for the reply.

I'm still confused. I read the links, they don't help much   

[Borek]

I hate to repeat myself three times, but I will try.

Write reaction equations. Pretty please, with a cherry on top.