Page 43 - ICSE Chemistry 6
P. 43

Let’s understand sedimenta  on and decanta  on by performing Ac  vity 2.5.
                           Activity 2.5


                 Aim: To separate a mixture of sand and water by sedimenta  on and decanta  on
                 Materials required: 2 beakers, some sand, some water, a glass rod

                 Procedure 1
                   •  Take a mixture of sand and water in a beaker.
                   •  S  r it and keep it undisturbed for 15–20 minutes.
                 Observa  on  1: You will observe that sand se  les down at the bo  om of the
                 beaker, leaving clear water over it. This process is sedimenta  on.

                 Procedure 2
                   •  Now take another beaker
                                                                                                                    glass rod
                       and put a glass rod in it.
                   •  Pour the water gently from       mixture of sand                              clear water
                       fi rst beaker into the second      and water                                 (supernatant)
                                                                                                     sand
                       beaker along the glass rod,                                                 (sediment)
                       as shown in the fi gure.
                 Observa  on 2: You will observe that sand and water get separated. This process is decanta  on.


                 Limitations of Sedimentation and Decantation

                     • The components of an insoluble solid and liquid cannot be completely separated.

                     • The components of a solid which is lighter than liquid do not se  le down, hence, they cannot be
                        separated.
                 Filtration

                 This method  is used to separate an insoluble solid and a liquid. In
                 this process, the mixture to be separated is passed through a fi lter
                 paper. The fi lter paper has   ny pores that allows only the liquid
                 to pass through it and the insoluble solid par  cles remain on the
                 fi lter paper. The insoluble solid le   behind on the fi lter paper is
                 called residue and the clear liquid that passes through the fi lter
                 paper is called fi ltrate.
                 In addi  on to the fi lter paper, we can also use glass wool, charcoal,
                                                                                                  Fig. 2.8: Filtration
                 sand, unglazed porcelain, co  on and strainer.
                 The technique of fi ltra  on is daily used in our houses to separate tea leaves from tea using a strainer.
                 Filtra  on is also used to remove pulp from fresh juice.


                                                          Thirst for Knowledge

                      Filter paper is a special kind of paper which has   ny pores of specifi c dimension. It allows only liquid to
                      pass through, whereas undissolved solid par  cles are retained on the fi lter paper.


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