Chapter 10, Problem 136A

Interpretation Introduction

Interpretation:

The mass of $4.95\times {10}^{25}\text{ HF molecules}$ should be calculated.

Concept introduction:

Number of moles of a compound is defined as the ratio of given mass of the compound to the molar or molecular mass of the compound.

The mathematical expression is given by:

Number of moles = $\frac{\text{given mass of the compound}}{\text{molar mass of the compound}}$

The one mole of any substance is equal to the Avogadro number, i.e., $6.022\times {10}^{23}$ atoms.

Answer to Problem 136A

Mass of $\text{HF}$ = $1.64\times {10}^3\text{ g}$

Explanation of Solution

Number of molecules of $\text{HF}$ = $4.95\times {10}^{25}$ molecules

Since, one mole of any substance is equal to the Avogadro number, i.e., $6.022\times {10}^{23}$ atoms.

Number of moles = $\text{number of molecules ×}\frac{1\text{ mole}}{6.022\times 10\text{molecules}}$

Put the values,

Number of moles = $4.95\times {10}^{25}\text{ molecules×}\frac{1\text{ mole}}{6.022\times 10\text{molecules}}$

$\text{Number of moles of HF=}$

$\text{82}\text{.1986 mole}$

Molar mass of $\text{HF}$ = $\text{1}\text{.0078 g/mole + 18}\text{.9984 g/mole}$

= 20.01 g/mole

Number of moles = $\frac{\text{mass of the compound}}{\text{molar mass of the compound}}$

$\text{82}\text{.1986 mole}$ = $\frac{\text{ mass of the compound}}{\text{20}\text{.01 g/mole}}$

Mass of $\text{HF}$ = $\text{82}\text{.1986 mole}\times 20.01\text{ g/mole}$

Mass of $\text{HF}$ = 1644.79 g

Mass of $\text{HF}$ = $1.64\times {10}^3\text{ g}$