Chapter 10, Problem 139A

Interpretation Introduction

Interpretation:

The number of formula units which are present in 500.0 g of lead(II) chloride should be calculated.

Concept introduction:

The number of moles of a compound is defined as the ratio of the 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 139A

Number of formula units of ${\text{PbCl}}_{\text{2}}$ = $10.83\times {10}^{23}\text{ formula units}$

Explanation of Solution

The molecular formula of lead(II) chloride = ${\text{PbCl}}_{\text{2}}$

Molar mass of ${\text{PbCl}}_{\text{2}}$ = $1\left(207.2\text{ g/mole}\right)+2\left(35.45\text{ g/mole}\right)$

= $278.1\text{ g/mole}$

Number of moles of ${\text{PbCl}}_{\text{2}}$ = $\frac{\text{500}\text{.0 g}}{\text{278}\text{.1 g/mole}}$

= $1.798\text{ mole}$

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

Number of formula units of ${\text{PbCl}}_{\text{2}}$ = $1.798\text{ mole ×}6.022\times 10\frac{\text{formula units}}{\text{mole}}$

= $10.83\times {10}^{23}\text{ formula units}$