# A 3.53-gg sample of aluminum completely reacts with oxygen to

A 3.53-gg sample of aluminum completely reacts with oxygen to form 6.67 gg of aluminum oxide.
Use these data to calculate the mass percent composition of aluminum in aluminum oxide.
Express the percent composition to three significant figures

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Jacob Homer
Step 1
Mass of aluminum in the sample is 3.53 g.
Mass of aluminum oxide is 6.67 g.
Step 2
Mass percent of a substance is equal to the mass of a substance divided by the total mass of compound multiplied by 100.
Write the expression of mass percent of aluminum.
$$\displaystyle\text{Mass percent}={\left({\frac{{\text{Mass of Al}}}{{\text{Mass of}{A}{l}_{{{2}}}{O}_{{{3}}}}}}\right)}{100}\%$$
Substitute 3.53 g for mass of Al and 6.67 g for mass of aluminum oxide to calculate mass percent.
$$\displaystyle\text{Mass percent}={\left({\frac{{{3.53}{g}}}{{{6.67}{g}}}}\right)}{100}\%$$
$$\displaystyle={52.92}\%$$
Therefore, mass percent of aluminum is 52.92%.
The answer in three significant figures is 52.9%.
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alexandrebaud43

Explanation:
The percent composition of aluminium in the resulting oxide will be the ratio between the mass of aluminijm and the total mass of the oxide, multiplied by 100.
$$\displaystyle\%{A}{l}={\frac{{{m}_{{{A}{l}}}}}{{{m}_{{ins{i}{d}{e}}}}}}\times{100}$$
In your case, you know that a 4.78-g sample of aluminium reacts completely with excess oxygen to form an unknown aluminium oxide.
Moreover, you know that this oxide has a mass of 6.67 g.
Since all the luminium that initially reacted with the oxygen is now a part of the oxide, you can say that its percent composition in the oxide will be $$\displaystyle\%{A}{l}={\frac{{{4.78}{{{g}}}}}{{{6.67}{{{g}}}}}}\times{100}-{71.664}\%$$
Rounded to three sig figs, the answer will be $$\displaystyle\%{A}{l}={71.5}\%$$

star233

Step 1
The percent compasition of Al in the resulting axide will be ratio
between the mass of Al and the total mass of axide, multiplied by lw.
$$\% Al=\frac{m_{Al}}{m_{oxide}} \times l w.$$
3.53g sample of Al reacts with oxygen to form $$Al_{2} O_{3}.$$
Oxide has a mass of 6.67.
$$\% Al=\frac{3.53g}{6.67g} \times lw$$
$$=52.92\%$$
Step 2
Mass percent composition of Aluminium is 52.92 percent.