# How do you calculate the percent composition by mass of each element in Al(OH_)3?

May 17, 2018

Al = 34.62%

O = 61.54%

H = 3.85%

#### Explanation:

The Percentage Composition by Mass of Each Element is indicated by :-

"Molar mass of The Element"/"Molar Weight of the Total Compound" xx 100%

So, The Molar Weight of the Total Compound = $\left\{27 + 3 \times \left(16 + 1\right)\right\}$ $g$ $m o {l}^{-} 1$ = $\left(27 + 51\right)$ $g$ $m o {l}^{-} 1$ = $78$ $g$ $m o {l}^{-} 1$

So, Percentage Composition of Aluminium = 27/78 xx 100% = 34.62% (approx.)

Percentage Composition of Oxygen = (3 xx 16)/78 xx 100% = 61.54% (approx.)

And Percentage Composition of Hydrogen = (3 xx 1)/78 xx 100% = 3.85% (approx.)