A student burns 10 g of ethanol in an open beaker. After the reaction. Class 9

A student burns 10 g of ethanol in an open beaker. After the reaction. Class 9

Pause and Ponder (Page 166)

Question 1.

A student burns 10 g of ethanol in an open beaker. After the reaction, no residue is left in the beaker. Does this mean the Law of Conservation of Mass is violated? Explain.

Answer:

No, the Law of Conservation of Mass is NOT violated. When ethanol burns, it reacts with oxygen from the air and produces carbon dioxide and water vapour, both of which escape into the atmosphere as gases. If we account for the mass of oxygen consumed from the air and the mass of carbon dioxide and water vapour released, the total mass of the products will be equal to the total mass of the reactants (ethanol + oxygen). The fact that no residue is left in the beaker does not mean mass is lost - the products have escaped as gases. The Law of Conservation of Mass is obeyed.

Question 2.

When 20 g of hydrogen reacts completely with 160 g of oxygen, how much water is formed according to the Law of Conservation of Mass? Class 9

Answer:

According to the Law of Conservation of Mass, the total mass of products = total mass of reactants. Total mass of reactants = 20 g (hydrogen) + 160 g (oxygen) = 180 g.

Therefore, mass of water formed = 180 g.