MediumChemistryHigh School (9–10)GeneralAtoms and Molecules › Laws of Chemical CombinationNumericalConceptualBoard Exam
Three students heat substances in closed vessels and weigh them before and after…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Three students heat substances in closed vessels and weigh them before and after.
| Experiment | Mass before | Mass after |
|---|---|---|
| A | ||
| B | ||
| C |
In which experiment does the law of conservation of mass seem not to hold? By how much? What could have gone wrong?
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 and C. The masses before and after are equal: the law holds.
Step 2. B. is missing.
Step 3. Why. Mass is never destroyed, so must have escaped, most likely a gas through a loose stopper or a crack.
Answer: Experiment B, by ; its vessel was probably not properly closed.
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