Chapter 11, Problem 115A

a)

Interpretation Introduction

Interpretation:

The relation between the molecular formula and empirical formula of acetaldehyde and butanoic acid needs to be explained.

Concept introduction : Empirical formula for a compound is the formula with smallest whole number mole ratio of the elements.

Molecular formula specifies the actual number of atoms of each element in one molecule or formula unit.

Answer to Problem 115A

The percent composition of acetaldehyde and butanoic acid are equal. So, the molecular and empirical formula of acetaldehyde and butanoic acid are the whole number multiples of each other.

Explanation of Solution

From given figure, one can see the percent composition of elements is same for both acetaldehyde and butanoic acid. So, the molecular and empirical formula of acetaldehyde and butanoic acid are the whole number multiples of each other.

b)

Interpretation Introduction

Interpretation:

The empirical formula of butanoic acid needs to be determined.

Concept introduction:

Empirical formula for a compound is the formula with smallest whole number mole ratio of the elements.

Answer to Problem 115A

Butanoic acid: CH₃CH₂CH₂COOH

Molecular formula: C₄H₈O₂

Empirical formula: C₂H₄O

Explanation of Solution

C% = 54.5 ;molar mass of C is 12g/mol

H% = 9.1 ;molar mass of H is 1g/mol

O% = 36.4 ;molar mass of O is 16g/mol

So,

$\begin{array}{l}MolesofC=\frac{54.5}{12}=4.54\\ MolesofH=\frac{9.1}{1}=9.1\\ MolesofO=\frac{36.4}{16}=2.275\end{array}$ for simple ratio divide each by smallest number of moles

$\begin{array}{l}MolesofC=\frac{4.54}{2.275}=1.99\sim 2\\ MolesofH=\frac{9.1}{2.275}=4\\ MolesofO=\frac{2.275}{2.275}=1\end{array}$

So, empirical formula of butanoic acid is C₂H₄O