Law of Conservation of Mass

Introduction

The law of conservation of mass is also termed as principle of mass/matter conservation. The law of conservation of mass states that mass cannot be created/destroyed, but it may be changed from one form to another. This concludes that for any chemical process in a closed system, the mass of the reactants must be equal the mass of the products.

Experiment for Law of the Conservation of Mass:

Discussion:

In this experiment, aqueous solutions of three different compounds will produce two separate and distinct chemical reactions. Balanced chemical equations for the two reactions are:

Na₂CO₃(aq) + CaCl₂(aq) ----2NaCl(aq) + CaCO₃(aq) (Eq.1)

CaCO₃(s) + H₂SO₄(aq) ------CaSO₄(s) + H₂O + CO₂(g) (Eq.2)

The combined masses of the three solutions will be measured before and after each reaction is completed.

PURPOSE

To recognize the law of conservation of mass and to determine the masses of reactants and products.

EQUIPMENT

Laboratory balance corks (to fit test tubes) (2), Erlenmeyer flask: 125-Ml, labels rubber stopper (for flask), safety goggles, and graduated cylinder: 10-mL, lab apron and coat test tubes 13 x 100-mm (2)

MATERIALS

1 M aqueous solutions of: Na₂CO₃, CaCl₂ and H₂SO₄

PROCEDURE

1. Measure exactly 10.0 mL of sodium carbonate (Na₂CO₃) solution in a graduated cylinder. Pour Na2CO3 into a clean, dry 125-mL Erlenmeyer flask. Stopper the flask.

2. Measure exactly 3.0 mL of 1 M calcium chloride (CaCl₂) solution by a pipette and pour into a clean, dry test tube. Put cork and label the tube.

3. Measure exactly 3.0 mL of 1 M sulfuric acid (H₂SO₄) solution by a pipette and pour into a clean, dry test tube. Put cork and label the tube.

4. Put the stoppered flask and the corked test tubes together on the pan of the laboratory balance. Tilt the test tubes to avoid liquids from touching the corks. Measure the total mass of these containers, stoppers, and solutions.

5. Now, remove the flask and the test tube containing the CaCl₂ solution from the balance pan. Pour the CaCl₂ solution into the Na₂CO₃ solution in the flask. Shake the flask to mix the two solutions thoroughly.

6. Replace the stopper and cork in their initial containers. Once again, measure the combined mass of the three containers, stoppers, and contents.

7. Remove the flask and the test tube containing H₂SO₄ from the balance pan. Pour the H₂SO₄ solution into the flask with care. Shake the flask until all bubbling stops. Note the readings.

8. Replace the stopper and cork and the solutions in their initial containers. Again measure the mass of the three containers, stoppers, and contents.

Result:

We will observe that the mass of the all three solutions will be conserved. Hence, this experiment proves the law of conservation of mass.