EasyChemistryHigh School (11–12)Atoms and Molecules › Laws of Chemical CombinationAtoms and Molecules › The Mole ConceptNumericalBoard Exam
Arun heats 24.5 g of potassium chlorate in a test tube…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Arun heats g of potassium chlorate in a test tube. It breaks down into potassium chloride and oxygen gas, which escapes. At the end, g of potassium chloride is left. What mass of oxygen was given off?
Need a reminder? The key ideaShow
Conservation of mass: in a reaction the total mass of the products equals the total mass of the reactants. Definite proportions: a compound always has the same elements in the same proportion by mass. Multiple proportions: when two elements form several compounds, the masses of one that combine with a fixed mass of the other are in a small whole-number ratio. Gay Lussac: reacting gases have volumes in a small whole-number ratio, at the same temperature and pressure.
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. The law. By conservation of mass, the mass of potassium chlorate equals the mass of potassium chloride plus the mass of oxygen.
Step 2. Subtract. .
Check. The tube loses mass only because the oxygen leaves it. In a sealed tube the mass would stay g.
Answer: g of oxygen.
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