Summary of Data
The initial mass of BaCl2.2H2O crystals in the vial: 14.601g
The final mass of BaCl2.2H2O crystals in the vial: 14.140g
The total amount of BaCl2.2H2O transferred into the 400-ml beaker: 0.461g
The mass of a piece of #42 filter paper on the large watch glass: 34.660g
The mass of the BaSO4/filter paper/watch glass before drying in the oven: 35.165g
The mass of the BaSO4/filter paper/watch glass after drying in the oven: 35.095g
The mass of the BaSO4 crystals: 0.435g
Calculations and Discussion
3) The direction of the error if heavy metal cations were present in a sample is positive because these heavy metal cations are held on surfaces of barium sulfate. This process of coprecipitation adds more mass to the crystals of barium sulfate, which results in the positive error.
4) If the nitrate anions are present, it will cause the negative error because a nitrate anion is lighter than a sulfate anion. Therefore, nitrate anions are more soluble. If they are more soluble, they will remain as ions in the solution with barium cations. In the filtering process, these will pass through the filter, and the resultant mass of precipitate of barium sulfate will be less than it is when there are no foreign anions in the solution.
If the chlorate anions are present, it will cause the positive error since a chlorate anion is heavier then a sulfate anion. Therefore, chlorate ions are less soluble. If they are less soluble, they will react with barium to precipitate. In the filtering process, these will not pass through the filter, and the resultant mass of precipitate of barium sulfate will be greater than it is when there are no foreign anions in the solution.
Conclusion
Precipitations, filtrations, and evaporations were used to prepare barium chloride dihydrate from crude barium carbonate. The experimental design in part I was, however, not sophisticated enough for us to expect a high percent yield.
In part II, the quantitative analysis of barium chloride dihydrate for the purity was performed. From the weight of BaSO4 obtained, the weight of pure BaCl2.2H2O in the sample. The percent purity of BaCl2.2H2O was calculated to be 98.7%. The error could have been large if heavy metal cations, which are likely to be coprecipitated with barium sulfate, were present; moreover, if the anions nitrate and chlorate were present, they could have been coprecipitated as barium salts, which result in negative and positive errors respectively.
