Experimental Verification of Law of Conservation of Mass

The following experiment can be conducted to verify the law of conservation of mass: 

Things Required

Things required to prove the Law of conservation of mass are,

• Barium chloride (BaCl₂.2H₂0),
• Sodium sulphate (Na₂SO₄.10H2O),
• Two beakers of 100 and 150 ml respectively.
• Physical balance
• Two watch glasses
• Spring balance (0-500 g),
• Polythene bag
• Distilled water
• A glass rod.

The reaction can be visualised as a precipitation reaction, where the insoluble salt separates out as a precipitate. The reaction occurs between the Barium Chloride (BaCl2₂(aq)) and Sodium Sulphate (Na₂SO₄(aq)). Both the compounds are taken in aqueous solutions, that is water is taken as the solvent. This is a kind of double displacement reaction.

The reaction involved is,

BaCl_2(aq) + Na₂SO_4(aq) ————-> BaSO_4(aq) + 2NaCl_(aq)

Rearranging the equation in the iconic form, we get, 

Ba⁺_(aq) + SO₄^2-_(aq) —————> BaSO4_(s)

The reactants involved in the reaction are barium chloride and sodium sulphate, whereas the products involved are barium sulphate and sodium chloride.

Now, we know, 

Mass of the reactants (barium chloride + sodium sulphate) = Mass of the products (barium sulphate + sodium chloride)

Steps Involved

Steps involved in the verification of Law of conservation are:

• 50 ml distilled water is taken in two 100 mL beakers.
• Weigh the two taken watch glasses on a physical balance.
• A quantity of 3.6 g of BaCl₂.2H₂0 is taken in a watch glass.
• Dissolve the quantity of aqueous solution of barium chloride in 50ml of distilled water. The contents are stored in beaker A.
• 8.05 g of Na₂SO4.10H₂O is taken in another watch glass of a definite mass.
• Dissolve the quantity of aqueous solution of sodium chloride in 50ml of distilled water. The contents are stored in beaker B.
• A 150ml beaker is taken and measured using the spring balance. This beaker will contain the final contents and is labelled as C.
• The solutions contained in beakers A and B are combined together through constant stirring using a glass rod.
• A precipitate emerges on the beaker C, owing due to the formation of the compound barium sulphate (BaSO₄).
• The total weight of the products can be calculated by measuring the weight of the beaker.
• The masses of the content of the beakers are measured before and after the reaction.

Assumptions: In the case of distilled water, density is assumed to be 1g /cc.

Things to Take Care

Before starting the experiment we should take care of the following things,

• Small quantities of chemicals should be used to perform the reaction.
• Initially, the spring balance pointer should be at zero marks.
• The reading of spring balance is taken only once its pointer is at the rest position.
• The reading of spring balance should be taken when it is placed in a vertical position.
• Precise quantities of the masses mentioned should be taken.
• Solution of BaCl₂ and Na₂SO₄ should be mixed with constant stirring.

Observations

The following inferences can be drawn from the experiment, 

• Mass of aqueous solution of barium chloride (BaCl₂) = 3.6 g
• Mass of BaCl₂ solution = 53.6 g
• Mass of aqueous solution of sodium sulphate (Na₂SO₄.10H₂O) = 8.05 g
• Mass of Na₂SO₄ solution = 58.05 g
• Mass of 50 ml distilled water = 50.0 g

Calculating the total mass of reactants, we have, 

BaCl₂ + Na₂SO₄ = 53.6 + 58.05 

                          = 111.65 g

Conclusions

When we compare the mass of reactants with those of products, the two masses are considered to be equivalent. This implies that the observed masses, m₂ = m₃.  Hence, the law of conservation of mass is preserved. 

Precautions

Following precautions must be taken while performing the experiment.

• Use the weighing machine with caution as it is sensitive to the slightest change.
• Use distilled water to make the solution.
• When solutions X and Y are mixed place the solution in a bottle with a cork.
• While calculating the resultant mass of the product, subtract the mass of the [conical flask + cork].
• The cork is used to prevent the gas, or vapours, from escaping the solution. The law is valid only for closed systems.
• Never taste any chemicals used in the experiment.

Law of conservation of mass states that “The mass can neither be created nor destroyed in a chemical reaction” French chemist Antoine Lavoisier was the first to state the law of conservation of mass in his book. There is just a rearrangement in the atoms of substances for the formation of compounds.

In the chemical process, the law of conservation of mass can be understood as the total mass of the reactant at the beginning of the reaction being equivalent to the mass of the product at the end of the reaction. 

Mass _reactants = Mass _products

Let’s learn about the law of conservation of mass in detail in this article,