Chapter 2.7, Problem 5PPB

(a)

Interpretation Introduction

Interpretation:

The mass of calcium should be calculated in a sample containing $\text{81}\text{.06}\text{g}\text{of helium}$.

Concept introduction:

$\begin{array}{l}\text{Avogadro’s number is 6}{\text{.022 × 10}}^{\text{23}}\\ \text{1 mole = }\text{6}{\text{.022 × 10}}^{\text{23}}\text{Avogadro’s number }\end{array}$

$\text{Number of}\text{moles }\text{=}\frac{\text{Mass}}{\text{Molar mass }}$

$\text{mol × }\frac{\text{6}{\text{.022 × 10}}^{\text{23}}\text{ atoms}}{\text{1 mol }}\text{=}\text{ atoms}$

(b)

Interpretation Introduction

Interpretation:

The number of gold atom should be calculated in a sample containing $\text{7}{\text{.095×10}}^{31}\text{ argon atoms }$.

Concept introduction:

$\begin{array}{l}\text{Avogadro’s number is 6}{\text{.022 × 10}}^{\text{23}}\\ \text{1 mole = }\text{6}{\text{.022 × 10}}^{\text{23}}\text{Avogadro’s number }\end{array}$

$\text{mol × }\frac{\text{6}{\text{.022 × 10}}^{\text{23}}\text{ atoms}}{\text{1 mol }}\text{=}\text{ atoms}$