Chapter 10, Problem 149A

Interpretation Introduction

Interpretation:

The number of sodium ions present in 25.0 g of sodium chloride 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 149A

Number of sodium ions = $2.58\times 10\text{ions}$

Explanation of Solution

The given compound is sodium chloride.

Molecular formula of sodium chloride = $\text{NaCl}$

Molar mass of $\text{NaCl}$ = $1\left(22.99\text{ g/mole}\right)+1\left(35.45\text{ g/mole}\right)$

= $58.44\text{ g/mole}$

Mass of $\text{NaCl}$ = 25.0 g

Number of moles of $\text{NaCl}$ = $\frac{\text{25}\text{.0 g}}{58.44\text{ g/mole}}$

= $\text{0}\text{.43 mole}$

$\text{NaCl}$ contains one mole of sodium and one mole of chlorine.

Or,

$\text{NaCl}$ dissociated as:

$\text{NaCl}\to {\text{Na}}^{\text{+}}{\text{+Cl}}^{-}$

Number of moles of ${\text{Na}}^{\text{+}}$ = $\text{0}\text{.42778 mole}\times 1$

= $\text{0}\text{.43 mole}$

Number of sodium ions = $\text{Number of moles × 6}\text{.022}\times {\text{10}}^{23}\frac{\text{ions}}{\text{mole}}$

= $\text{0}\text{.43 mole}\times \text{ 6}\text{.022}\times {\text{10}}^{23}\frac{\text{ions}}{\text{mole}}$

= $2.58\times 10\text{ions}$