Theory for a formal report on the precipitation of BaSO4
Hi, i have to do a formal report for the MST and i realised tht i cant answer most of the questions (i feel like a gone-case student :( , then i found this cool website which hopefully can help me progress and understand my chemistry)
My question is: why do i have to do the steps highlighted in red? What does it do?
(A) Precipitation of BaSO4
(1) Pipette 25.0 mL of the given sulphate solution into a 250 mL beaker.
(2) Add about 50 mL of water and 5 drops of concentrated HCl.
Caution: Concentrated HCl is very corrosive, add in the fume hood.
(3) Heat to boiling and, with vigorous stirring, add dropwise from a measuring cylinder 10 mL of 10% barium chloride solution.
(4) Cover the beaker with a watch glass and digest (heat to just below boiling) for 20 minutes.
(5) Test for complete precipitation by adding a few drops of BaCl2 to the clear supernatant liquid.
(B) Washing and Filtration of BaSO4 precipitate
(1) Decant the clear supernatant by filtration (use a weighed filter paper) at the vacuum pump, using a pre-weighed crucible.
(2) Wash and swirl the precipitate with about 20 mL of warm deionised water.
(3) Use a 'rubber-policeman' to dislodge any particles on the beaker.
(4) Allow to settle.
(5) Decant the liquid through the filter paper.
(6) Repeat the washing and decanting at least 2 more times.
(7) Discard the filtrate.
(C) Drying and weighing of BaSO4 precipitate
(1) Dry the crucible in the oven at 150oC for about 1/2 hour.
(2) Cool the crucible with BaSO4 precipitate in a desiccator for about 10 minutes.
(3) Weigh the crucible when it is cooled down.
(4) The difference between this weight and the empty crucible (plus filter paper) is the weight of BaSO4 precipitate. (Note: You may repeat Steps 1 to 4 until a constant weight of the precipitate is obtained.)