Question

Suppose some of your unknown sample has failed to dissolve even after you have titrated to your end point. What effect would this have on the calculated molecular weight of your unknown? Explain.

Answer 1

Firstly, your sample is not dissolved means, the reaction is incomplete. So the end point will be very lower compared to the exact value of end point, because more sample is remain there to dissolve. Less dissolution leads to decrease of concentration or normality, that is weight of solute dissolved in unit volume of the solution in litter.

The calculated molecular weight depend on the weight of solute dissolved and normality,

because, Normality = Weight per litter/ Equivalent weight

and Molarity = Weight per litter/ Molecular mass

from this Molecular mass =Weight per litter / Molarity

So if your sample is not dissolved fully, it will give lesser concentration or normality value and it will increase the real molecular mass of solute.  

i hope you got the answer.