Question

A sample of the mineral hematite Iron (III) oxide has a mass of 12.4g. How many moles of the mineral are present?

Answer 1

Thus problem is providing us with the mass of iron (III) oxide as 12.4 g so the moles are required and found to be 0.0776 mol after the calculations:

Mole-mass relationships:

In chemistry, we use mole-mass relationships in order to calculate grams from moles and vice versa. In this case, since we are given the mass of iron (III) oxide as 12.4 g one can calculate the moles by firstly quantifying its molar mass:

$Fe_2O_3\rightarrow 2*55.85 g/mol+3*16.00 g/mol=159.7g/mol$

Then, we prepare a conversion factor in order to cancel out the grams and thus, get moles:

$12.4gFe_2O_3*\frac{1molFe_2O_3}{159.7gFe_2O_3} \\\\=0.0776molFe_2O_3$

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