Resources: Materials for the Mission Assignment, such as a 500l plastic drinks bottle, a balloon, sodium bicarbonate, vinegar, measuring cylinder, balance or digital scale, cling film, ice, vessel for ice, spatula, elastic band and safety goggles.
Support Handout: Page 1 of the handout.
Core Handout: Handout contains details of how to complete the tasks.
Use the previous lessons from the unit to recap on learning. The students should have an understanding that chemical reactions involve the rearrangement of atoms and that new substances are formed.
Ask the students: Which of the following statements best defines the law of the conservation of mass? They should look at definitions on the starter slide and select which one they think is correct. You could do a vote or they could have 30 seconds to write down the one they think is right. The answer on the top right is correct.
Use the presentation slides to explain conservation of mass and then carry out the experiments to prove that mass is conserved in changes of state and chemical reactions.
Career Film: This is Daniel Wilmot. Daniel works as a Waste Strategy Nuclear Graduate for the Nuclear Decommissioning Authority. Find out more about Daniel's job by taking a tour of his workplace.
Expert Film: This is Daniel Wilmot. Daniel works as a Waste Strategy Nuclear Graduate for the Nuclear Decommissioning Authority. Listen to Daniel as he explains how mass is conserved in chemical reactions.
The students should follow both of the methods on the handout. The first method will allow the students to prove that conservation of mass takes place during a physical change, as the mass of the ice, beaker and cling film will be the same as the mass of the water, beaker and cling film at the end of the allocated time. The students will then have to explain how this proves the conservation of mass.
For the second method, the students will carry out a chemical reaction which will produce a gas. This is captured in the balloon, ensuring that mass does not escape. They will then answer questions based on this.
Support: The first handout contains some ‘fill in the gap’ questions to help students understand conservation of mass.
Challenge: Ask the students to suggest how to alter the experiment to measure the mass of gas produced.
Discuss the results of experiments - did they confirm conservation of mass? Were there any errors in measurements?
The principle of conservation of mass is incredibly important in science and allowed for chemistry to become a respected branch of science. Conservation of mass allows scientists to predict how much of each product that they will get when carrying out a specific reaction which allows many of the industrial processes that are essential to everyday life to be efficient.
A chemical reaction can include anything from a single reactant to lots of separate reactants. In the case of a single reaction, which is often called a decomposition reaction, the atoms within the single reactant will rearrange to form the products. This means that the mass of the reactant will still be there but will be in the form of the products, even if the products are a different state of matter.
Chemical reactions between 2 or more reactants are also very common; many of the chemical reactions that take place inside of your body are incredibly complex but allow our bodies to function. During these reactions, the atoms of the reactants will rearrange to form the products. Often, as is the case with chemical changes, the products will be in a different form to the reactants; even if a colourless gas is made, the mass of the atoms is still there.
The conservation of mass can be proved quite easily through experiments. When many metals are heated in oxygen, they can appear to gain mass as they are going from the metal to the metal oxide. If the same metal was to be heated in a vacuum, or in an atmosphere of a reactive gas, there would be no mass gain. The problem of gases and mass can pose a huge issue to scientists but during this lesson, the students will prove that the mass is conserved.
When carbonates react with acids, they produce a salt, water and carbon dioxide. Normally, this carbon dioxide can be observed through the fizzing of the solution. If a bottle contains these two reactants was weighed, it would appear to lose weight as the carbon dioxide diffuses into the air of the room. If the bottle was sealed, the mass would remain the same although the pressure that the bottle is in would cause some safety issues. In this lesson, students will capture the gas in a weighed balloon. This will also allow the students to mix the bicarbonate and acid without making a mess. Since the carbon dioxide is being captured, the mass of the entire closed system will stay exactly the same, proving that mass is conserved, even during a chemical change.