Chapter 10, Problem 10STP

Interpretation Introduction

Interpretation:

The mass of one mole of barium hexafluorosilicate needs to be determined.

Concept introduction:

$\begin{array}{l}1\text{ mol element }=6\cdot 023\times {10}^{23}\text{ molecules/particles}\\ \left(\text{Avogadro's number}\right)\end{array}$

Molar mass is calculated from mass and number of moles as follows:

$\text{Molar mass =}\frac{\text{mass of substance}}{\text{number of moles}}$

Answer to Problem 10STP

Correct answer is (c) $\text{4}\cdot 64\times {10}^{-22}\text{ g}$ from periodic table

Explanation of Solution

The mass of one mole of an element is called its molar mass. (Molecular Weight)

One mole of any substance is defined as equal to the Avogadro's number that is equal to $6\cdot 023\times {10}^{23}$

Molar mass of $\text{Ba}=137\cdot 33\text{ g/mol}$

Molar mass of $\text{Si}=28\cdot 09\text{ g/mol}$

Molar mass of $\text{F}=19\text{ g/mol}$

Molar mass of $\begin{array}{l}{\text{BaSiF}}_{\text{6}}=137\cdot 33\frac{g}{\text{mol}}+28\frac{g}{\text{mol}}+6\times 19\frac{g}{\text{mol}}\\ =297\text{ g/mol}\end{array}$

$\therefore$ One mole of molecule of ${\text{BaSiF}}_{\text{6}}$ weighs $\text{297 g/mol}$

$6\cdot 023\times {10}^{23}$ molecules of ${\text{BaSiF}}_{\text{6}}$ has mass $297\text{ g}$

Therefore, $1$ molecule will have mass

$\frac{279\text{ g}}{6\cdot 023\times {10}^{23}}=4\cdot 64\times {10}^{-22}\text{ g}$

Conclusion

Correct answer is (c) $4\cdot 64\times {10}^{-22}\text{ g}$