[Sona]

A solution of 0.1332 g of CrCl3.6H2O was passed through a cation exchange resin in the acid form. 8ml of standard NaOH solution( contaiong 0.5g NaOH/lit) was required for the titration of the liberated acid. Determine the correct formulation of the complex. Given atomic wt of Cr is 52.

What I've done is that
converting the strengh of NaoH solution into molarity. It becomes0.0125 molar.
Now each mol of acid will react with each mol of base.
And each mol of complex will give 3 mol of acid.
From here it can be written that: 1000ml 1(M) base = 1000ml 1(M) acid = 1/3 mol of CrCl3.6H20
                                      hene 8ml 0.0125(M) base = 3.33 * 10^-5 mol CrCl3.6H2O
Hence 3.33 * 10^-5 mol complex = 0.1332 g
                         1 mol complex = 3996 g
Upto this is it okay?
But after that they asked about formulation.
I couldn't understand how to proceed.
Please help...

[Borek]

To some extent you are solving a wrong problem.

Hint: CrCl₃ is not necessarily dissociating into Cr³⁺+3Cl^-. Cl^- can be a ligand in which case charge of the cation will be lower than +3.

[mjc123]

Is there a factor of 10 error somewhere? Should it be 0.01332 g complex, or 80 ml NaOH, or 50 g/L? Otherwise it seems that 5 moles of complex liberate 1 mole of acid, which seems wrong.

[Sona]

If it happens that it is a[Cr(H₂O)₆]Cl₃ then how should I proceed?

If it is 0.01332 then 1mol weights 399.6 g, to get the formulation how should I use this value?

[Borek]

What does the liberated acid tell you about the cation?

[Sona]

1 equivalent cation produces 3 equivalent acid. So liberated acid gives how much cation is present in the solution.

[Borek]

1 equivalent cation produces 3 equivalent acid.

That's where you are wrong.

So liberated acid gives how much cation is present in the solution.

You already know how much cation is in the solution, that's a given. It doesn't make sense to titrate the solution to find the same information for the second time.

Sure, titration tells you something about the cation, but it is not what you think it is.