(N/A) The law of conservation of mass states that mass can neither be created nor destroyed in a chemical reaction.
Activity:
$1$. Prepare separate solutions of $X$ and $Y$ in water. Take a little amount of $X$ solution in a conical flask and some $Y$ solution in a small ignition tube.
$2$. Hang the ignition tube in the flask carefully by a thread. Put a cork on the flask.
$3$. Weigh the flask with its contents on a balance.
$4$. Now,tilt and swirl the flask so that the solutions $X$ and $Y$ get mixed.
$5$. Weigh the flask again.
Observation:
It is observed that the mass of the flask and its contents remains the same before and after the reaction,demonstrating that mass is conserved.
Example:
Reaction between Barium Chloride $(BaCl_2)$ and Sodium Sulphate $(Na_2SO_4)$:
$BaCl_2(aq) + Na_2SO_4(aq) \rightarrow BaSO_4(s) + 2NaCl(aq)$