Chapter 10, Problem 92A

(a)

Interpretation Introduction

Interpretation: The empirical formula of a compound containing 0.40 mol of Cu and 0.80 mol of Br needs to be determined.

Concept Introduction: For any compound, the empirical formula shows the simplest ratio of atoms of different elements present in the compound.

Explanation of Solution

The number of moles of Cu is 0.40 mol and that of Br is 0.80 mol. The simplest ratio of the number of moles of both elements can give the empirical formula of the compound. Thus,

  $\begin{array}{c}{n}_{\text{Cu}}:n_{\text{Br}}=0.40:0.80\\ =1:2\end{array}$

Therefore, the empirical formula of the compound will be ${\text{CuBr}}_{\text{2}}$

(b)

Interpretation Introduction

Interpretation: The empirical formula of a compound containing 4 atoms of carbon for every 12 atoms of hydrogen needs to be determined.

Concept Introduction: According to Avogadro’s law, 1 mol of any substance contains the same number of atoms that is $6.022\times {10}^{23}$ . Thus, the ratio of the number of moles and the number of atoms will be the same. For any compound, the empirical formula shows the simplest ratio of atoms of different elements present in the compound.

Explanation of Solution

According to the question, the number of atoms of C and H is 4 and 12 respectively. This can be said that C and H are in the 4:12 ratio.

  $\begin{array}{c}\text{C:H}=4:12\\ =1:3\end{array}$

Therefore, the empirical formula of compound is ${\text{CH}}_{\text{3}}$ .