Question

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

Answer 1

Answer: The number of formula units in the given amount of magnesium chloride is
`1.0357* 10^(23)`

Step-by-step 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=(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* 10^(23)`

We are given:

Number of moles of magnesium chloride = 0.172 moles

Number of formula units =
`0.172* 6.022* 10^(23)=1.0357* 10^(23)`

Hence, the number of formula units in the given amount of magnesium chloride is
`1.0357* 10^(23)`

Answer 2

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