EasyChemistryHigh School (9–10)GeneralAtoms and Molecules › Laws of Chemical CombinationConceptualBoard Exam
A student burns a candle on an open pan balance…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A student burns a candle on an open pan balance. The candle goes from to , and the burning wax uses of oxygen from the air.
- Is the law of conservation of mass broken?
- What mass of carbon dioxide and water vapour together was made?
- How could the student show that mass is conserved?
Need a reminder? The key ideaShow
In a chemical reaction mass is neither created nor destroyed: the total mass of the reactants equals the total mass of the products. Test it in a closed vessel, so that no gas escapes or enters.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. (a) No. The wax turned into carbon dioxide and water vapour, which escaped into the air, so the balance reading fell.
Step 2. (b) Wax burnt: . Products: .
Step 3. (c) Burn the candle inside a closed jar with enough air, on the balance. Nothing can leave, so the reading stays the same.
Answer: (a) No. (b) . (c) Burn it in a closed jar.
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