| Aim | To verify the law of conservation of mass in a chemical reaction. |
| Apparatus Required | Two watch glasses, beakers, weighing balance and glass rod. Distilled water and one of the following sets of chemicals. Set I → Copper sulphate and Sodium carbonate Set II → Barium chloride and Sodium sulphate Set III → Lead nitrate and Sodium chloride |
| Theory | The Law of conservation of mass states that matter cannot be created nor destroyed in a chemical change, with the exception of nuclear reactions as matter can change to energy. During a chemical reaction, the atoms of one or more substances simply get rearranged to form products. The total mass of the reactants before the reaction is equal to the total mass of the products after the reaction. Antoine Lavoisier proposed this law. There are various types of changes that chemicals can undergo, such as physical, chemical, and nuclear changes. During a physical change, matter only changes its phase from solid to liquid or from liquid to gas. In a chemical change, the atoms of the reactants rearrange and form new compounds. In a nuclear change, the nucleus of an atom can be changed by adding or reducing the number of protons in it or by splitting the nucleus. For example, uranium can undergo fission to become barium and krypton. During a chemical reaction, the reactants may take or give off heat, gas may be released, bubbles may be formed, the color may change, or a precipitate may be formed. |
| Method 1 | Weigh two watch glasses on a balance. In one of the watch glasses, weigh 3.6g of BaCl2.2H2O, which has a known mass. Pour 50 mL of distilled water into a 100 mL beaker labeled as “A.” Dissolve the BaCl2.2H2O in beaker A. Weigh 8.05g of Na2SO4.H2O in the other watch glass, which has a known mass. Pour 50 mL of distilled water into a second beaker labeled as “B,” and dissolve the Na2SO4.H2O in it. Weigh the second beaker and mark it as “C.” Combine the contents of beakers A and B into beaker C and stir with a glass rod. The synthesis of BaSO4 results in the formation of a white precipitate in beaker C. Weigh beaker C again with the product and record the mass. Calculate the mass of the finished product by subtracting the mass of beaker C before and after adding the solutions from A and B. Record the observations: | Observations: Mass of Reactants = 44 g Mass of Products = 44 g Mass of BaCl2.2H2O = 3.6 g Mass of BaCl2, solution = 53.6 g Mass of Na2SO4.10H2O = 8.05 g Mass of Na2SO4 solution = 58.05 g Total mass of reactants is 53.6 g + 58.05 g = 111.65 g (BaCl2, soln.) (Na2SO4 solution.) Mass of beaker ‘C’ is C1 = 500 g Mass of reaction mixture on adding in beaker ‘C’ is C2 = 611.65 g Mass of the product formed = C2 – C1 = 111.65 g Note: Mass of 50 ml of distilled water = 50.0 g (density of water = 1 g/mL) |
| Method 2 | Prepare a 5% solution of either compound X or Y from the list provided. Next, take a conical flask and add a small quantity of the Y solution and a small amount of the X solution to it. Then, suspend an ignition tube in the flask without allowing its contents to flow into the flask, as shown in the diagram. Cover the flask using a cork and weigh the flask and its contents carefully. After that, gently swirl and tilt the flask to mix the X and Y solutions. Weigh the conical flask again and record the observations. Remember to note the mass of the conical flask before the reaction takes place. | Observations: Initial weight of conical flask + ignition tube with X and Y solutions Weight of conical flask + ignition tube when solution X and Y are mixed and reaction has taken place The mass of the reactants equals the mass of the products. |
