Law of Conservation of Mass

Understanding the Concept

When a chemical change occurs, the total mass of substances before the reaction equals the total mass after the reaction. This idea is captured in the Law of Conservation of Mass, which says:

Mass cannot be created or destroyed during a chemical reaction.

This means that the mass you start with is the mass you end up with, even if the substances change into new substances.

The Activity

Let's perform an activity to see this law in action. We will mix two chemical solutions and observe what happens.

Materials Needed

• Chemicals from group X and Y:
  • (i) Copper sulphate (X) and Sodium carbonate (Y)
  • (ii) Barium chloride (X) and Sodium sulphate (Y)
  • (iii) Lead nitrate (X) and Sodium chloride (Y)
• Beaker or conical flask
• Cork
• Ignition tube
• Scale for weighing

Steps to Follow

1. Make Solutions:

   • Prepare a 5% solution of one pair of substances in 10 mL of water each (one from X and one from Y).

2. Set Up:

   • Take a small amount of the solution from Y in a conical flask.
   • Take the solution from X in an ignition tube.

3. Placement:

   • Hang the ignition tube in the flask carefully. Ensure that the solutions do not mix immediately.
   • Seal the flask's opening with a cork.

4. Weighing:

   • Weigh the flask with the solutions. Record the weight.

5. Mixing:

   • Tilt the flask to swirl and mix the solutions.

6. Weigh Again:

   • Weigh the flask and its contents again after mixing. Record the new weight.

Observations and Discussions

Questions to Consider

1. What happens in the reaction flask?

   • The two solutions mix and may react to form a new substance.

2. Do you think a chemical reaction has taken place?

   • Yes, if a new substance is formed (e.g., if a precipitate appears).

3. Why should we put a cork on the mouth of the flask?

   • The cork prevents any gases from escaping. This ensures that no mass is lost during the reaction.

4. Does the mass of the flask and its contents change?

   • No, the mass before and after mixing should remain the same, confirming the law.

Important Points to Remember

• The Law of Conservation of Mass helps us understand that reactions are just rearrangements of atoms.
• No matter how the substances change, the total mass does not change.
• This principle is essential in chemistry.

Fun Scenario-Based Questions

1. Scenario 1: You have two balloons. One has a gas and the other is empty. You let the gas fill the empty balloon. Does the total mass change?

   • Answer: No, the total mass stays the same. The gas just moves from one balloon to the other.

2. Scenario 2: You burn a piece of paper. What happens to the mass?

   • Answer: The mass is not lost; it turns into gases and ash. If collected, the total mass would be the same.

3. Scenario 3: If you freeze water into ice, does the mass change?

   • Answer: No, freezing does not change the mass, only the state of the water changes.

4. Scenario 4: If you mix baking soda and vinegar, does the mass change?

   • Answer: No, even if it fizzes and bubbles, the total mass remains constant.

5. Scenario 5: When cooking an egg, does it lose mass?

   • Answer: No, the egg's mass stays the same. Any steam produced can be contained to keep the mass steady.

Now you know how the Law of Conservation of Mass works! Have fun conducting the activity and observing this important chemical principle!