Calculate the percent composition by mass of each element in Al (OH) 3. Use at least three significant figures.

34.59 % Al; 61.54 % O; 3.877 % H

Explanation:

% by mass = mass of element/total mass * 100 %

Let's rewrite the formula of Al (OH) ₃ as AlO₃H₃.

Set up a table for easy calculation.

Atom Mass/u Subtotal

1Al 1 * 26.98 = 26.98 u

3O 3 * 16.00 = 48.00 u

3H 3 * 1.008 = 3.024 u

Total = 78.004 u

Mass % Al = 26.98/78.004 * 100 % = 34.59 %

Mass % O = 48.00/78.004 * 100 % = 61.54 %

Mass % H = 3.024/78.004 * 100 % = 3.877 %