# What is (i) %O in "aluminum sulfate" by mass? And (ii) given a 1.00*g mass of this salt, how many formula units does this mass represent?

Jun 17, 2017

Well, %O="Mass of oxygen in aluminum sulfate"/"Mass of aluminum sulfate"=56%

#### Explanation:

O%=(12xx16.00*g*mol^-1)/(342.15*g*mol^-1)xx100%=??%

For formula units present in $1.000 \cdot g$ of the salt, we work out the molar quantity.......

$\text{Moles of aluminum sulfate} = \frac{1.000 \cdot g}{342.15 \cdot g \cdot m o {l}^{-} 1} = 2.923 \times {10}^{-} 3 \cdot m o l$

And since we know that $1 \cdot m o l$ contains ${N}_{A} = \text{Avogadro's Number"=6.022xx10^23*"particles} \cdot m o {l}^{-} 1$, we has ..............

$2.923 \times {10}^{-} 3 \cdot m o l \times 6.022 \times {10}^{23} \cdot m o {l}^{-} 1 = 1.760 \times {10}^{21} \cdot \text{formula units}$.