Separation by settling, filtration and centrifugation

The mechanical separation of a solid from a liquid (e.g.: a precipitate in water) can be carried out in a lot of ways. The most frequent processes are settling, filtration and centrifugation. First of all, prepare the precipitate for this test. Pour some barium hydroxide into 2 test tubes and into a centrifuge tube; then add some drops of dilute sulfuric acid into each tube: the immediate result is the formation of the whitish precipitate of barium sulphate. Then it is possible to carry out the separation by settling, filtration and centrifugation. Settling: students can observe the precipitate settling onto the bottom by gravity and water clarifying. The supernatant liquor is sucked with a pipet and then it is disposed of. Filtration: the content of the test tune is poured into the funnel with the filter; filtration occurs in few minutes; then the filter will be dried in a stove or in a sheltered and dry place. Furthermore the filtration test can also be carried out at reduced pressure via a water vacuum pump that must be connected with a tap of water. Centrifugation: insert the centrifuge tune into one of centrifuge holes; switch the centrifuge on and make it turn for a certain time. Then students can observe the precipitate well settled on the bottom.