Q: Which of the following is the correct mathematical relationship for determining the molecular formula from the empirical formula?

$\text{Molecular formula mass} = n \times \text{Empirical formula mass}$

Question 1

A compound is found to contain 40.00% carbon, 6.71% hydrogen, and 53.29% oxygen by mass. What is the empirical formula of this compound?

Accepted Answer

$\mathrm{CH}_2\mathrm{O}$

Question 2

A 0.6003 g sample of a compound containing only C, H, and O is combusted, producing 0.6003 g $\mathrm{H}_2\mathrm{O}$ and 2.445 g $\mathrm{CO}_2$. What is the mass of hydrogen in the original sample?

Accepted Answer

$0.06716\ \mathrm{g}$

Question 3

Which of the following best describes the process of determining the empirical formula from percent composition data?

Accepted Answer

Convert percent to grams, divide by atomic masses to get moles, divide by smallest number of moles, and multiply to get whole numbers if needed.

Question 4

A hydrocarbon with the molecular formula $\mathrm{C}_5\mathrm{H}_{12}$ is analyzed and found to produce $\mathrm{CO}_2$ and $\mathrm{H}_2\mathrm{O}$ upon combustion. What is the empirical formula of this hydrocarbon?

Accepted Answer

$\mathrm{C}_5\mathrm{H}_{12}$

Question 5

A compound has an empirical formula of $\mathrm{CH}_2\mathrm{O}$ and a molar mass of $180.16\ \mathrm{g\ mol}^{-1}$. What is its molecular formula?

Accepted Answer

$\mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_6$

Question 6

During CHNS analysis, all carbon in a sample is converted to $\mathrm{CO}_2$. If a sample produces $0.05556$ mol $\mathrm{CO}_2$, how many moles of carbon were in the original sample?

Accepted Answer

$0.05556$ mol

Question 7

A compound is found to have the empirical formula $\mathrm{C}_3\mathrm{H}_8\mathrm{O}$ and a molar mass of $180\ \mathrm{g\ mol}^{-1}$. What is the value of $n$ in the relationship $	ext{Molecular formula} = n 	imes 	ext{Empirical formula}$?

Accepted Answer

$n = 6$

Question 8

Which of the following is the correct mathematical relationship for determining the molecular formula from the empirical formula?

Accepted Answer

$	ext{Molecular formula mass} = n 	imes 	ext{Empirical formula mass}$

Question 9

A sample of aniline ($\mathrm{C}_6\mathrm{H}_7\mathrm{N}$) weighing $9.71\ \mathrm{g}$ is combusted, producing $6.63\ \mathrm{g}$ of $\mathrm{H}_2\mathrm{O}$ and $14.6\ \mathrm{g}$ of $\mathrm{CO}_2$. What is the empirical formula of aniline?

Accepted Answer

$\mathrm{C}_6\mathrm{H}_7\mathrm{N}$

Question 10

If a compound has the empirical formula $\mathrm{CH}_2\mathrm{O}$ and its molar mass is $177.5\ \mathrm{g\ mol}^{-1}$, what is its molecular formula?

Accepted Answer

$\mathrm{C}_6\mathrm{H}_8\mathrm{O}_6$

Question 11

A compound is analyzed and found to contain 54.5% C, 9.1% H, and 36.4% O by mass. What is the empirical formula?

Accepted Answer

$\mathrm{C}_2\mathrm{H}_4\mathrm{O}$

Question 12

Which of the following statements about CHNS analysis is correct?

Accepted Answer

All carbon in the sample is converted to $\mathrm{CO}_2$ during combustion.

Question 13

A compound has the empirical formula $\mathrm{CH}_2\mathrm{O}$ and a molar mass of $88.06\ \mathrm{g\ mol}^{-1}$. What is the value of $n$ in the molecular formula equation?

Accepted Answer

$n = 1$

Question 14

If a sample contains 0.05556 mol of $\mathrm{CO}_2$ and 0.06663 mol of $\mathrm{H}_2\mathrm{O}$, what is the mole ratio of C:H in the sample?

Accepted Answer

1:2

Question 15

A compound is found to have the empirical formula $\mathrm{C}_2\mathrm{H}_4\mathrm{O}$ and a molar mass of $88\ \mathrm{g\ mol}^{-1}$. What is its molecular formula?

Accepted Answer

$\mathrm{C}_4\mathrm{H}_8\mathrm{O}_2$

Question 16

Which of the following is NOT a correct step in determining an empirical formula from percent composition?

Accepted Answer

Add the atomic numbers of each element to get the empirical formula.

CH 3-2: Empirical and Molecular Formulas: Determination from Experimental Data

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