Question

Explain and verify law of conservation of mass?​

Answer 1

The law of conservation of mass states that. The mass in an isolated system can neither be created nor be destroyed but can be transformed from one form to another. According to the law of conservation of mass, the mass of the reactants must be equal to the mass of the products for a low energy thermodynamic process.

Answer 2

Question-

Verify the law of conservation of mass.

Answer-

Aim

To verify the law of conservation of mass in a chemical reaction

Materials Required

Barium chloride (BaCl₂.2H₂O), sodium sulphate (Na₂SO₄.10H₂O), distilled water, two beakers (150 mL), one beaker (250 mL), physical balance, spring balance (0 - 500 g) and a polythene bag, two watch glasses of known masses and a glass stirrer.

Procedure

Step 1: 100 mL distilled water is poured in two beakers (150 mL).

Step 2: The physical balance and a watch glass of known mass are used, weigh 7.2 g of BaCl₂ .2H₂O and dissolved in a beaker (150 mL) containing 100 mL distilled water.

Step 3: Similarly, 16.1 g of Na₂SO₄.10H₂O is weighed in another watch glass of known mass and dissolved in another beaker (150 mL) containing 100 mL distilled water.

Step 4: The third beaker (250 mL) is taken and weighed using a spring balance and polythene bag.

Step 5: Both solutions of 150 mL beakers are mixed in the third beaker (250 mL). The contents are mixed using a glass stirrer.

Step 6: White precipitate of BaSO₄ appears on mixing due to precipitation reaction.

Step 7: The beaker containing the reaction mixture is weighed again to determine the mass of the precipitation reaction products.

Step 8: The masses before and after the chemical reaction are compared.

Observations

(i) Mass of 100 mL distilled water = 100.0 g (The density of distilled water is 1 g/mL.)

(ii) Mass of BaCl₂ .2H₂O = 7.2 g

(iii) Mass of BaCl₂ solution = 107.2 g

(iv) Mass of Na₂ SO₄.10H₂O = 16.1 g

(v) Mass of Na₂SO₄ solution = 116.1 g

(vi) Total Mass of reactants = 223.3 g (solutions of BaCl₂  and Na₂SO₄)

(vii) Mass of empty 250 mL beaker, m₁ = _____ g

(viii) Initial mass of reaction mixture and empty beaker (before the precipitation), m₂ = (m₁ + 223.3 g) = _____ g

(ix) Final mass of reaction mixture in the beaker after the precipitation m₃ = _____g

Results and Discussions

Compare the initial mass (m²) of the reaction mixture (before the precipitation) with the final mass (m³) of the reaction mixture (after precipitation). If the two masses are the same within reasonable limits, then the law of conservation of mass stays verified.

The verification of the law rests on accurate mass measurements in the laboratory. The chemical reaction involved is:

BaCl² + (aq) + SO₄²- (aq) ⇒ BaSO₄(S)