Chapter 22, Problem 9STP

Interpretation Introduction

Interpretation:

The mass of one molecule of barium hexafluorosilicate $\left({\text{BaSiF}}_{\text{6}}\right)$ needs to be determined.

Concept introduction:

In 1 mol of a substance there are $6.023\times {10}^{23}$ units. Also, number of moles is related to mass and molar mass as follows:

$n=\frac{m}{M}$

Here, m is mass and M is molar mass.

Answer to Problem 9STP

Correct Answer: Option (a) is correct.

Explanation of Solution

Reason for correct options:

The given substance is barium hexafluorosilicate $\left({\text{BaSiF}}_{\text{6}}\right)$.

The molar mass can be calculated from atomic mass of Ba, Si and F atoms.

$\begin{array}{l}M=137.327\text{ g/mol}+28.0855\text{ g/mol}+6\left(19\text{ g/mol}\right)\\ =279.4125\text{ g/mol}\end{array}$

Now, in 1 mol there are $6.023\times {10}^{23}$ molecules of ${\text{BaSiF}}_{\text{6}}$ thus, $6.023\times {10}^{23}$ molecules of ${\text{BaSiF}}_{\text{6}}$ has 279.4125 g of mass.

Therefore, the mass of 1 molecule will be:

$m=\frac{279.4125\text{ g}}{6.023\times {10}^{23}}=4.64\times {10}^{-22}\text{g}$

Therefore, mass of 1 molecule of ${\text{BaSiF}}_{\text{6}}$ is $4.64\times {10}^{-22}\text{g}$. The correct option will be (a).

Conclusion

Reason for incorrect options:

After calculations, mass of 1 molecule of ${\text{BaSiF}}_{\text{6}}$ is $4.64\times {10}^{-22}\text{g}$ therefore; options (b), (c) and (d) are incorrect.