Changes in Matter, Not in Weight
Lesson Objective
The student will explore the law of conservation of mass by tearing paper, observing a reaction between baking soda and vinegar,
and predicting whether melting, freezing, and dissolving will cause a change in mass.
Background Information for Teacher
Communication of scientific thinking is an important skill. Praise student for valid reasoning and identifying supportive data. If their
reasoning is incorrect, help them clarify their thinking.
Words in bold are responses to the questions.
Student Prior Knowledge
1 sheet of light cardboard, such as half a manila file folder
1 plastic 2-liter pop bottle
1 tablespoon baking soda.
2 tablespoons vinegar
scale or balance
Step-by-Step Guided Lesson
Step 1: Start Video
(Tips: Interact with the video by pausing, to ask questions or discuss information viewed with student.)
Step 2: Teach Lesson
A chemical reaction occurs when new kinds of matter are formed. The composition of the matter changes and the new kinds of matter have different properties
from the old matter. Evidence of a chemical change may be the production or use of energy such as heat or light. The mass remains the same before the reaction
and after. A chemical reaction takes place when vinegar and baking soda are mixed. One of the new substances formed is carbon dioxide gas. If the carbon
dioxide gas is contained, the mass of the substances will stay the same according to the Law of Conservation of Mass. If the gas is allowed to escape, the mass
will be less.
Give the student the following instructions and questions.
Using the balance, record the weight of the sheet of cardboard. Tear or cut the cardboard into small pieces. Using the balance, again record the weight. Is the
weight the same or different? How would you explain this? [Mass is conserved.]
Place 2 tablespoons of vinegar into the bottle. Using the funnel, pour 1 tablespoon of baking soda into the balloon. Carefully attach the balloon to the top of the
bottle. Do not allow any baking soda to pour into the bottle. Using the balance, record the mass of the bottle, soda, balloon, and vinegar.
Mix the vinegar into the baking soda by lifting the balloon and allowing the baking soda to pour into the bottle. Make sure the balloon remains attached to the neck
of the bottle. After the fizzing stops, again record the mass of the items. Is the weight the same or different? How would you explain this? [Mass is conserved.]
Remove the balloon. Put the balloon and bottle on the balance. Weigh the items. Is the weight the same or different? How would you explain this? [Air has
weight. The air escaped from the balloon, making the total weight less than before.]
Compare the data from the cardboard experiment with the data from the baking soda and vinegar experiment. What is similar and what is different? How would
you explain this?
Write an explanation for the following questions.
Why did the weight of the paper remain the same after it was torn apart? Why was the weight of the vinegar, balloon, baking soda, and bottle the same before the
reaction as it was after? Why did the weight change when the balloon was removed?
Predict the results of the following actions:
10 g of water is frozen. What will its weight be when it melts? Explain your answer.
5 g of salt is dissolved in 10 g of water. What will the weight of the salt water be? Explain your answer.
Plan an experiment that will demonstrate that matter is neither created nor destroyed even though it may undergo change (Only plan the experiment. Look at Step
4 for further instructions).
Step 3: Complete the worksheet attached below.
Step 4: Start the next lesson with the game or activity attached below for review so the student can
demonstrate understanding of this lesson before moving forward.
Allow the student to conduct the experiment they planned in Step 2, to show understanding of the lesson.