Page 105 - ICSE Chemistry 6
P. 105

Activity 5.4


                 Aim: To show that air that we breath out contains carbon dioxide
                 Materials required: A conical fl ask, some lime water, a cork, a drinking straw

                 Procedure
                   •  Take a conical fl ask containing freshly prepared lime water.
                   •  Take a drinking straw and a cork with a hole.

                   •  Insert the straw in the cork and close the mouth of the conical fl ask with the cork.
                   •  Now exhale air from your mouth into the open end of the drinking straw.

                 Observa  on: You will observe that the lime water in the conical fl ask turns milky.
                 Conclusion: This happens because the carbon dioxide reacts with lime water and turns it milky. Lime
                 water is an aqueous solu  on of calcium hydroxide.

                            Carbon dioxide + Lime water  Calcium carbonate (white and insoluble)




                                                          Thirst for Knowledge

                      If the level of carbon dioxide in the atmosphere increases beyond its original level, it leads to trapping
                      more heat in the atmosphere. This increases the average temperature of the earth’s atmosphere thus
                      causing changes in climate.


                 Water Vapour

                 Water vapour are also present in the atmosphere. They are essen  al for running the water cycle in nature.
                 Water vapour are formed due to evapora  on and boiling of water. On coming in contact with a cool
                 surface, they condense and appear as water drops on the cold surface. Recall what happens when you
                 take out a water bo  le from refrigerator and keep it in the open (at room temperature) for some   me.
                 You no  ce water droplets on the outer surface of the water bo  le. Can you tell from where these water
                 droplets come? The water vapour present in the air on coming in contact with cold surface of the water
                 bo  le get condensed as water droplets.

                           Activity 5.5


                 Aim: To show that air contains water vapour
                 Materials required: A beaker, some ice cubes
                 Procedure
                   •  Take a glass beaker and fi ll it with ice cubes.

                   •  Let the beaker stand for some   me.
                 Observa  on: Fine droplets of water are formed on the outer surface of the beaker. Water vapour present
                 in air condense on the cold surface of the beaker.
                 Conclusion: This shows that air contains water vapour.



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