Chapter 6.2, Problem 1RQ

(a)

Interpretation Introduction

Interpretation: The number of moles of Ba and Cl in BaCl₂ needs to be determined.

Concept Introduction: The number of moles of an element can be determined from the molecular formula of the compound. The subscript for an element is equal to the number of moles of that element present in 1 mol of the compound.

Answer to Problem 1RQ

The number of moles of Ba is 0.15 mol and that of Cl is 0.30 mol.

Explanation of Solution

The number of moles of BaCl₂ is 0.15 mol.

From the formula, it can be seen that 1 mol of the compound contains 2 mol of Cl thus, number of moles of Cl in 0.15 mol of the compound can be calculated as follows:

  $n=0.15\times 2=0.30\text{ mol}$

Thus, the number of moles of Cl is 0.30 mol.

Similarly, 1 mol of compound has 1 mol of Ba thus, number of moles of Ba in 0.15 mol will be 0.15 mol.

(b)

Interpretation Introduction

Interpretation: The number of moles of C and O in 2.0 mol of CO₂ needs to be determined.

Concept Introduction: The number of moles of an element can be determined from the molecular formula of the compound. The subscript for an element is equal to the number of moles of that element present in 1 mol of the compound.

Answer to Problem 1RQ

The number of moles of C and O is 2 mol and 4 mol respectively.

Explanation of Solution

The given formula of compound is CO₂. There is 1 mol of C and 2 mol of O in 1.0 mol of CO₂.

Thus, the number of moles of C and O in 2 mol of CO₂ will be:

  $\begin{array}{l}{n}_C=2\text{ mol }\\ n_O=4\text{ mol}\end{array}$

(c)

Interpretation Introduction

Interpretation: The number of moles of H, N and O in 3.50 moles needs to be determined.

Concept Introduction: The number of moles of an element can be determined from the molecular formula of the compound. The subscript for an element is equal to the number of moles of that element present in 1 mol of the compound.

Answer to Problem 1RQ

The number of moles of H, N and O is 3.5 mol, 3.5 mol and 10.5 moles respectively.

Explanation of Solution

The given compound is HNO₃.

Thus, 1 mol of compound has 1 mol of H, 1 mol of N and 3 mol of O.

The number of moles of compound is 3.50 mol thus, number of moles of H and N will also be 3.50 mol.

The number of moles of O will be:

  $n_O=3\times 3.50=10.5\text{ mol}$

(d)

Interpretation Introduction

Interpretation: The number of moles of N, H, S and O in 0.65 mol of compound needs to be determined.

Concept Introduction: The molar mass is the mass of a given chemical element or chemical compound divided by the amount of substance. The molar mass of a compound can be calculated by adding the standard atomic masses (in g/mol) of the constituent atoms.

Answer to Problem 1RQ

The number of moles of N, H, S and O is 1.3 mol, 5.2 mol, 0.65 mol and 2.6 mol respectively.

Explanation of Solution

The given compound is ${\left({\text{NH}}_{\text{4}}\right)}_{\text{2}}{\text{SO}}_{\text{4}}$ . In 1 mol there are 2 mol of N, 8 mol of H, 1 mol of S and 4 mol of O.

The given number of moles of compound is 0.65 mol thus, number of moles of each element can be calculated as follows:

  $\begin{array}{l}{n}_N=2\times 0.65=1.3\text{ mol}\\ n_H=8\times 0.65=5.2\text{ mol}\\ n_S=1\times 0.65=0.65\text{ mol}\\ n_O=4\times 0.65=2.6\text{ mol}\end{array}$