problems and solutions:
human error in calculating, measuring, weighing, etc. To minimize it repeat experiment a couple of times and ensure more accurate measuring is done
some of the barium sulfate that forms may stick to the sides of the beaker and may be lost as a result. minimize it by using a wash bottle with distilled water to ensure all the particles are transferred
longer digestion times would allow formation of larger particles - and thus fewer losses through the sintered funnel - accurate results