Chapter 10.3, Problem 52SSC

Interpretation Introduction

Interpretation: The number of moles in $1000\text{ mg}$ of ${\text{Ca}}^{+2}$ needs to be calculated.

Concept introduction: Number of moles in the ratio of weight to the gram molecular weight of given ion/element or compound.

Answer to Problem 52SSC

Number of moles in $1000\text{ mg}$ of ${\text{Ca}}^{+2}$ is $2\cdot 5\times {10}^{-2}$ .

Explanation of Solution

Given information:

Weight of ${\text{Ca}}^{\text{+2}}\text{ions = 1000 mg = 1000}\times {\text{10}}^{-3}\text{ g}$ .

Formula used:

  $\begin{array}{l}\text{number of moles =}\frac{\text{mass}}{\text{molar mass}}\\ \text{n =}\frac{\text{m}}{\text{M}}\end{array}$

Calculation:

Mass of ${\text{Ca}}^{\text{+2}}\left(\text{m}\right)\text{ = 1000 mg}$

  $\text{=1 g}$

Molar mass of ${\text{Ca}}^{\text{+2}}\left(\text{M}\right)\text{ = 40 g/mol}$

Substitute in the above formula

  $\begin{array}{l}\text{n =}\frac{\text{m}}{\text{M}}=\frac{1000\times {10}^{-3}\text{ g}}{40\text{ g/mol}}\\ =\frac{1}{40}\\ =2\cdot 5\times {10}^{-2}\end{array}$

Or,

  $\begin{array}{l}\text{n=}\frac{1000\text{ mg}}{40\text{ g}}=25\text{ milli moles}\\ \text{=0}\cdot \text{025 moles}\end{array}$

Conclusion

Therefore, the moles of molar present in $1000\text{ mg}$ of ${\text{Ca}}^{+2}$ is $2\cdot 5\times {10}^{-2}$ mol.