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A works wants 1.47 kg of potassium dichromate, K₂Cr₂O₇, which has a molar mass of 294 g/mol…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A works wants of potassium dichromate, , which has a molar mass of . The ore holds chromite, , by mass. The molar mass of chromite is . Only of the chromium in the ore ends up in the dichromate. Each formula unit of chromite and each of dichromate holds 2 chromium atoms. Find the moles of dichromate wanted, the mass of pure chromite needed and the mass of ore.
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
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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. Dichromate wanted. .
Step 2. Chromite, with the yield. One chromite unit gives one dichromate unit, since each holds 2 chromium atoms. At an 80.0 % yield, of chromite is needed. The mass is .
Step 3. The ore. The ore is 56.0 % chromite, so .
Answer: , and of ore.
Watch out. A yield of less than 100 % means more raw material, so divide by it. Do not multiply.
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