Question

with the help of activity , prove law of conservation of mass .

Answer 1

Activity 1: The conservation of atoms in chemical reactions:
                                                                                            We will use the reaction of hydrogen and oxygen to form water in this activity.MaterialsColoured modelling clay rolled into balls or marbles and prestik to represent atoms. Each colour will represent a different element.MethodBuild your reactants. Use marbles and prestik or modelling clay to represent the reactants and put these on one side of your table. Make at least ten (H2) units and at least five (O2) units.Place the H2 and O2 units on a table. The table represents the “test tube” where the reaction is going to take place.Now count the number of atoms (H and O) you have in your “test tube”. Let the reaction take place. Each person can now take the H and O unit and use them to make water units. Break the H and O units apart and build H2O units with the parts. These are the products. Place the products on the tableYou should have noticed that the number of atoms in the reactants is the same as the number of atoms in the product. The number of atoms is conserved during the reaction. However, you will also see that the number of molecules in the reactants and products are not the same. The number of molecules is not conserved during the reaction.

Answer 2

Law of conservation of mass states that If one or more substance undergo a reaction, then the mass of reactants and the products remains same. 

Example:- 

CaO + CO2 ------------> CaCO3

Here mass of CaO is 56 amu and mass of CO2 is 44 amu, and mass of CaCO3 is 100 amu . 
This shows that, 
mass of reactants= mass of products 
56 + 44= 100

i hope this is useful