# Chemistry

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In a reaction, 39.5 g of chromium(III) oxide reacts with 14.0 g of aluminum to produce chromium and aluminum oxide. If 27.0 g of chromium is produced, what mass of aluminum oxide is produced?

I don't know where to begin. Do I put this into a chemical formula? balance it out?
like,
2 CR2O3 + 3Al --> 4 Cr + 3 AlO2??

In the book it said something about ratios, but I have no clue how to do that. Please help explain this, much appreciated!

• Chemistry - ,

• Chemistry - ,

1. Write the equation and balance it.
2. Convert 27.0 g Cr to moles. moles = grams Cr/atomic mass Cr.
3. Using the coefficients in the balanced equation (that's the ratio the book is talking about), convert moles Cr to moles Al. It will look like this.
moles Cr(from step 1) x (y moles Al/z moles Cr) = moles Al.
moles Cr you have from step 1, y moles Al where y is the coefficient in the balanced equation for Al and z is the coefficient in the balanced equation for Cr. Note how the factor (the part in parentheses) cancels Cr but leaves Al. That is how we convert moles of one material in a chemical equation to any other material we wish.
4. Now convert moles Al to grams. g = moles x molar mass.
This procedure is a general one for stoichiometry problems in chemistry.

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