MediumChemistryHigh School (11–12)Atoms and Molecules › Laws of Chemical CombinationAtoms and Molecules › The Mole ConceptNumericalConceptualBoard Exam
Two black powders are reduced to the metal…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Two black powders are reduced to the metal. Sample A: g of powder gives g of metal. Sample B: g of powder gives g of metal. Find the percentage of metal in each. Could they be the same compound?
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. Sample A. metal.
Step 2. Sample B. metal.
Step 3. The law. Both have the same make-up by mass. This fits the law of definite proportions, so they can be the same compound. Equal percentages alone do not prove it, but different ones would rule it out.
Answer: metal in each, so they may be the same compound.
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