Question

In this experiment you used an excess of the BaCl2 solution. How would your results be affected if you did not use an excess of the BaCl2 solution? Would this error cause your calculation of the mass percent of sulfate in the unknown to be too high or too low? Explain. In the last step of the procedure, you vigorously heated the BaSO4 precititate wrapped in the filter paper in a crucible. How would your results be affected if tiny pieces of the filter paper still remained mixed with the BaSO4 after heating? Would this error cause your calculation of the mass percent of sulfate in the unknown to be too high or too low? Explain.

Answer 1

Solution:- (i)

The net precipitation equation would be...

Ba²⁺(aq) + SO₄^2-(aq) ------> BaSO₄(s)

If BaCl₂ (Ba²⁺) is not taken in excess then the precipitation would not be completed as some of the sulfate ions would still be remaining in the solution. This would decrease the mass percentage of sulfate in the unknown sample.

(ii) If some tiny pieces of filter paper still remained mixed with the precipitate(BaSO₄) then the mass of sulfate would increase and it gives high mass percentage of the sulfate.

mass percentage of sulfate = (mass of sulfate/mass of sample)*100