Brooke B. 2 Answers By Expert Tutors Just to add to the answer provided by Russ F, and to show an easier way to solve this problem, we can use % composition. atomic mass Fe = 55.85 g/mol molar mass Fe2O3 = 159.69 g/mol There are 2 Fe in Fe2O3 so the total mass of Fe = 2 x 55.85 = 111.7 g Fe % Fe = 111.7 g / 159.69 g = 69.95% Mass of Fe in 54.39 g of Fe2O3 = 0.6995 x 54.39 g = 38.04 g Fe --> ANSWER
Grams Fe in 54.39g Iron (III) Oxide? Step 1: Determine Molecular Formula The Roman numeral indicates the charge (oxidation state) of the metal (Fe). The oxidation state of oxygen can be determined from its Group number on the periodic table (6A). This tells you that oxygen needs 2 more electrons to achieve an octet. When this occurs, oxygen attains a -2 charge. Use the criss-cross method to arrive at the formula. Fe3+ O2- → Fe2O3 2 mol Fe + 3 mol O → Fe2O3 Step 2: Convert grams Fe2O3 to moles Fe2O3 2 Fe: 56g/mol x 2 = 112g/mol 3 O: 16g/mol x 3 = 48g/mol Fe2O3 = 160g/mol 54.39g Fe2O3 [1 mol Fe2O3/160g Fe2O3] = 0.340 mol Fe2O3 We see that there are 2 mol Fe and 3 mol O to create 1 mole Fe2O3. Step 3: Use the mole ratio to determine mole Fe 0.340 mol Fe2O3 [2 mol Fe/1 mol Fe2O3] = 0.680 mol Fe Step 4: Convert mole Fe to grams Fe 0.680 mol Fe [56g Fe/1 mol Fe] = 38.1g Fe
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