Chapter 14, Problem 6STP

Interpretation Introduction

Interpretation:

Thecorrect empirical formula for this substancehave to be determined.

Concept introduction:

Empirical Formula: The formula of a compound can be calculatedusing a compound’s percent composition. First, determine the smallest whole-number ratio of themoles of the elements in the compound. This ratio gives the subscriptsin the empirical formula. The empirical formula for a compound can be defined as aformula with the smallest whole-number mole ratio of the elements.

Answer to Problem 6STP

Answer is C. The correct empirical formula for this substance is C₁₀H₁₈O.

Explanation of Solution

Assume a 100.0 g sample.

Have to determine the number of moles first by converting the mass of each element to moles.

Data given: C = 77.9 %, H = 11.7 % and O = 10.4 %

$\mathrm{Moles}ofC=\frac{77.9gmcarbon}{12.01gm/mol}=6.486$

$\mathrm{Moles}ofH=\frac{11.7gmH}{1.008gm/mol}=11.607$

$\mathrm{Moles}ofO=\frac{10.4gmO}{16.00gm/mol}=0.65$

The simplest ratio of moles are:

$\frac{6.486molC}{0.65}=9.98,\frac{10.607molH}{0.65}=17.86and\frac{0.65molO}{0.65}=1.0$

The empirical formula is C₁₀H₁₈O.

Conclusion

Reasons for incorrect options:

As, we have calculated the empirical formula for this substance from the given percentage data. We got the empirical formula is C₁₀H₁₈O.

Answer is C. The correct empirical formula for this substance is C₁₀H₁₈O.

That means other options that is,

A. CH₂O

B. C₈HO

D. C₇H₁₂Oare found to be incorrect.