Question

A student prepared an aqueous solution of barium chloride and sodium sulphate. She weighed them separately and mixed them in a beaker. A white precipitate was immediately formed. She filtered the precipitate, dried it, and weighed it again.

1. Will the weight of the precipitate be the same as that of the reactants before mixing?
2. If not so, where does the mistake?
3. Which law of chemical combination is supported by the experiment.
4. Which is the major condition that should be fulfilled to verify the law of conservation of mass.

Answer 1

The reaction involved is as follows:
${\mathrm{BaCl}}_2\left(\mathrm{aq}\right)+{\mathrm{NaSO}}_4\left(\mathrm{aq}\right)\to {\mathrm{BaSO}}_4\left(\mathrm{ppt}\right)+2\mathrm{NaCl}\left(\mathrm{aq}\right)$

1. No, it will not be the same.
2. The student should have weighed the total contents of the beaker after the reaction and not the precipitate only.
3. The Law of conservation of mass is supported by the experiment. According to this law, mass can neither be created nor be destroyed but can transfer from one form to another
4. The experiment must be carried out in a closed container and not in an open container.