Is there a change in mass when a chemical change (chemical reaction) takes place?
• Take one of the following sets, X and Y of chemicals– X Y
(i) copper sulphate sodium carbonate
(ii) barium chloride sodium sulphate
(iii) lead nitrate sodium chloride
• Prepare separately a 5% solution of any one pair of substances listed under X and Y in water.
• Take a little amount of solution of Y in a conical flask and some solution of X in an ignition tube.
• Hang the ignition tube in the flask carefully; see that the solutions do not get mixed. Put a cork on the flask (see Fig. 3.1).
: Ignition tube containing solution of X, dipped in a conical flask containing solution of Y
• Weigh the flask with its contents carefully.
• Now tilt and swirl the flask, so that the solutions X and Y get mixed.
• Weigh again.
• What happens in the reaction flask?
• Do you think that a chemical reaction has taken place?
• Why should we put a cork on the mouth of the flask?
• Does the mass of the flask and its contents change?
Law of conservation of mass states that mass can neither be created nor destroyed in a chemical reaction.
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