A 4.91 g sample of aluminum completely reacts with oxygen to form 6.85 g of aluminum oxide. Use this data to calculate the mass percent composition of aluminum in aluminum oxide.

i got 61.2% first and it was wrong. then i got 53.0% and it was wrong

i got the answer. thanks anyways!

You didn't get the right answer using those numbers did you? 4.91 g Al should form more than 6.85 g Al2O3.

To determine the mass percent composition of aluminum in aluminum oxide, we need to compare the mass of aluminum to the total mass of aluminum oxide.

First, let's calculate the mass of aluminum in the aluminum oxide sample:
Mass of aluminum = Mass of aluminum oxide - Mass of oxygen

Given:
Mass of aluminum oxide = 6.85 g
Mass of aluminum = 4.91 g (given in the problem)

To find the mass of oxygen, subtract the mass of aluminum from the mass of aluminum oxide:
Mass of oxygen = Mass of aluminum oxide - mass of aluminum

Mass of oxygen = 6.85 g - 4.91 g = 1.94 g

Now, we can calculate the mass percent composition of aluminum in aluminum oxide:
Mass percent composition of aluminum = (Mass of aluminum / Total mass of aluminum oxide) * 100

Total mass of aluminum oxide = Mass of aluminum + Mass of oxygen
Total mass of aluminum oxide = 4.91 g + 1.94 g = 6.85 g

Mass percent composition of aluminum = (4.91 g / 6.85 g) * 100

Calculating this expression gives:
Mass percent composition of aluminum = 71.64%

Therefore, the correct mass percent composition of aluminum in aluminum oxide is approximately 71.64%.