# How many formula units are present in a 12.6*g mass of MgCl_2?

Jun 17, 2017

#### Answer:

Approx. $8 \times {10}^{22}$ $\text{formula units............}$

#### Explanation:

We find the molar quantity by dividing the mass of substance by the molar mass.....

$\frac{12.6 \cdot g}{95.21 \cdot g \cdot m o {l}^{-} 1} = 0.132 \cdot m o l$

How did I get the $95.21 \cdot g \cdot m o {l}^{-} 1$ number?

And this there are $0.132 \cdot m o l$ $M g$, and $2 \times 0.132$ $C l$ atoms....

But a mole is SIMPLY A NUMBER, i.e. ${N}_{A} = 6.022 \times {10}^{23} \cdot m o {l}^{-} 1$.

And so the number of formula units.........

$6.022 \times {10}^{23} \cdot m o {l}^{-} 1 \times 0.132 \cdot m o l = 7.97 \times {10}^{22}$ formula units.

How many magnesium atoms, and how many chlorine atoms?