EasyChemistryHigh School (11–12)The d- and f-Block Elements › Transition Elements (d-Block)NumericalA-LevelIB
A brass is 64.0 % copper by mass, and the rest is zinc…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A brass is copper by mass, and the rest is zinc. A piece is melted down. The molar mass of copper is and that of zinc is . Find the mass of zinc, the moles of copper and the moles of zinc.
Need a reminder? The key ideaShow
Moles = mass in g divided by molar mass in g/mol, or concentration in mol/L times volume in litres. Take every mole ratio from the balanced equation, and follow the chain one step at a time.
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. Masses. Copper is . Zinc is .
Step 2. Moles. Copper: . Zinc: .
Answer: , and .
What this tells us. There are about 1.8 copper atoms for each zinc atom. The ratio is not a whole number, and a different brass would give a different ratio. An alloy has no fixed formula.
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