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Question:

The white powder often found on objects made of aluminum is aluminum oxide. Al2O3?

Calculate the molar mass of the aluminum oxide. A 5.00g strip of aluminum is reacted in air, producing an oxide weighing 9.36g. Calculate the percent oxygen and aluminum in the compound.Calculate the % error for percent of aluminum calculated.

Answer:

1) Yes, indeed. Al?O? is the correct formula for aluminum oxide. Because the ionic formula is Al?? and O??. (Aluminum has an oxidation number of 3+ ; and oxygen has an oxidation number of 2- . So a neutral ionic compound will have the formula Al?O?. Each element will take the number of the opposite ion.
molar mass.. .. molar mass Al2O3 = 2 x 26.98 + 3 x 16.00 = 101.96 g/mol mass %'s based on formula .. % Al in Al2O3 = (2 x 26.98 / 101.96) x 100% = ___ % .. % O in Al2O3 = (3 x 16.00 / 101.96) x 100% = ___ % mass % based on experimental data .. % Al in oxide = (5.00g / 9.36g) x 100% = ___% .. % O in oxide = ( (9.36g - 5.00g) / 9.36g) x 100% = __ % and finally .. % error = (|measured - accepted| / |accepted|) x 100% = ___% ********* here's the answer for the ALUMINUM calcs .. % Al in Al2O3 = (2 x 26.98 / 101.96) x 100% = 52.92% .. % Al in oxide = (5.00g / 9.36g) x 100% = 53.42% .. % error = ( | 53.42% - 52.92% | / | 52.92% | ) x 100% = 0.95% you get to do the oxygen calcs

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