The crystals coagulate so that when filtering is done the smaller particles don't pass through the filtering device with the water that does. After digestion is finished, the solution is filtered; in this experiment filter paper was used. Then deionized water or dilute acids are used to wash the precipitate to ensure that all aqueous ions are removed from the surface of the precipitate. The precipitate is then dried until a constant weight is obtained which ensure that there is no remaining water in the precipitate. Then using stoichiometry a chemical equation is made and it is possible to figure out the amount of each compound in the equation.
The second part of this lab dealt with analyzing how much sulfate was in the barium sulfate and then calculation of errors. There are 2 kinds of error systematic and random. Systematic are errors that after being discovered are generally fixable. A random error is uncontrollable these lead to uncertainties in calculations which are labeled as absolute error. When the relative error which is the magnitude of uncertainty is divided by the actual measurement and multiplied by 100 percent the random error can be calculated. The calculations of percent sulfate were determined for the whole class and then statistical treatment of the data was done to determine how close the experiment actually yielded correct answers.
Procedure.
A clean dry watch glass was weighed to the nearest .001g and depending on how much the scale wavered a number was recorded as uncertainty which was .002g. Then .847g of unknown compound was added to watch glass with an uncertainty of .002g. The compound was then transferred to a 400mL beaker and a wash bottle sprayed deionized water onto watch glass to ensure that the entire compound made it into the 400mL beaker. Then approximately 200mL of deionized water was added to the compound and 2mL of HCl were added to make sure a precipitate didn't form at this point.