Question

How many formula units make up 16.4 g of magnesium chloride (MgCl2)?

Answer 1

molar mass of MgCl2  = 24.32 + 2 x (35.45) = 95.22 g

16.4g MgCl2 x (1 mol MgCl2/95.22 g MgCl2) = 0.172 mol MgCl2 
 
0.172 mol MgCl2 x (6.022 x 10^23/1 mol MgCl2) = 10.36 x 10^22 atoms 

Answer 2

Answer: The number of formula units in the given amount of magnesium chloride is $1.0357\times 10^{23}$

Explanation:

To calculate the number of moles, we use the equation:

$\text{Number of moles}=\frac{\text{Given mass}}{\text{Molar mass}}$  

Given mass of magnesium chloride = 16.4 g

Molar mass of magnesium chloride = 95.2 g/mol

Putting values in above equation, we get:

$\text{Moles of }MgCl_2=\frac{16.4g}{95.2g/mol}=0.172mol$

Formula units is defined as lowest whole number ratio of ions in an ionic compound. It is calculated by multiplying the number of moles by Avogadro's number which is $6.022\times 10^{23}$

We are given:

Number of moles of magnesium chloride = 0.172 moles

Number of formula units = $0.172\times 6.022\times 10^{23}=1.0357\times 10^{23}$

Hence, the number of formula units in the given amount of magnesium chloride is $1.0357\times 10^{23}$