Chapter 6.2, Problem 5RQ

(a)

Interpretation Introduction

Interpretation: The mass and number of molecules needs to be determined.

Concept Introduction: The relation between number of moles, mass and molar mass is as follows:

  $n=\frac{m}{M}$

Here, m is mass and M is molar mass.

Answer to Problem 5RQ

  ${\text{Mass of NH}}_{\text{3}}\text{=79}\text{.9g}$

  ${\text{Number of molecules or atoms of NH}}_{\text{3}}\text{=28}{\text{.30×10}}^{\text{23}}$

Explanation of Solution

  ${\text{Number of moles of NH}}_{\text{3}}\text{=}\frac{\text{Given mass}}{\text{Molar mass}}$

  $4.7=\frac{\text{Given mass}}{\text{17}}$

  ${\text{Given mass of NH}}_3=4.7\times 17$

  $=79.9\text{ g}$

Now,

  ${\text{Number of molecules of NH}}_{\text{3}}\text{=Moles×Avogadro'snumber}$

  $=4.7\times 6.022\times {10}^{23}$

  $=28.30\times {10}^{23}$

(b)

Interpretation Introduction

Interpretation: The moles and number of molecules need to be determined.

Concept Introduction: The relation between number of moles, mass and molar mass is as follows:

  $n=\frac{m}{M}$

Here, m is mass and M is molar mass.

Answer to Problem 5RQ

  ${\text{Number of moles of H}}_{\text{2}}\text{O=0}\text{.1}$

  ${\text{Number of molecules of H}}_{\text{2}}\text{O=0}{\text{.6022×10}}^{\text{23}}$

Explanation of Solution

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

  $=\frac{1.80}{18}$

  $=0.1$

  ${\text{Number of molecules of H}}_{\text{2}}\text{O=Moles×Avogadro's number}$

  $=0.1\times 6.022\times {10}^{23}$

  $=0.6022\times {10}^{23}$

(c)

Interpretation Introduction

Interpretation: The number of moles and mass needs to be determined.

Concept Introduction: The relation between number of moles, mass and molar mass is as follows:

  $n=\frac{m}{M}$

Here, m is mass and M is molar mass.

Answer to Problem 5RQ

  ${\text{Mass of CH}}_{\text{4}}\text{=13}\text{.84 g}$

  ${\text{Number of molecules of CH}}_{\text{4}}\text{=0}\text{.00865}$

Explanation of Solution

  ${\text{Number of molecules or atoms of CH}}_{\text{4}}\text{=Moles×Avogadro'snumber}$

Or,

  ${\text{Moles of CH}}_{\text{4}}\text{=}\frac{{\text{Number of molecules of CH}}_{\text{4}}}{\text{Avogadro's number}}$

  ${\text{Moles of CH}}_{\text{4}}=\frac{5.21\times {10}^{22}}{6.022\times {10}^{23}}$

  $=0.865\times {10}^{-1}$

  $=0.0865$

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

  $0.0865=\frac{\text{Given mass}}{\text{16}}$

  $=0.0865\times 16$

  $=1.384gm$