Let’s solve this step by step.
We’re looking at a worksheet about the
Law of Conservation of Mass. That means:
> In a closed system, mass is neither created nor destroyed during a chemical reaction.
So, the total mass before the reaction = the total mass after the reaction.
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Looking at the first problem on the left page (the one with the beaker and scale):
It says:
- A student mixes 50 g of vinegar and 10 g of baking soda in a sealed bag.
- The bag swells up as gas is produced.
- After the reaction, the total mass is measured again.
Question: What is the final mass?
Step-by-step:
1. Before mixing:
Vinegar = 50 g
Baking soda = 10 g
Total initial mass = 50 + 10 =
60 g
2. The reaction happens inside a
sealed bag — so nothing escapes! Even though gas is made, it’s trapped inside.
3. Law of Conservation of Mass says:
Final mass = Initial mass → because no mass leaves or enters.
4. So, final mass =
60 g
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Now let’s check the second problem (middle column) to make sure we understand the pattern.
It shows two flasks connected by a tube, with a balloon on top. One flask has 20 g of liquid, the other has 5 g of powder. They mix, gas fills the balloon.
Total initial mass = 20 + 5 = 25 g
Since it’s a closed system (balloon traps gas), final mass should still be 25 g.
That matches the law.
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Third problem (right side) seems to be for students to fill in themselves — but since you didn’t ask for that, we’ll focus on the first one.
Also, note: if the system were OPEN (like an open beaker), gas could escape and mass would seem to decrease. But here, everything is sealed — so mass stays the same.
✔ Final Answer: 60 g
Parent Tip: Review the logic above to help your child master the concept of law of conservation of mass worksheet for middle school.
