Question 1

Which statement best describes the difference between an empirical formula and a molecular formula?

Accepted Answer

The empirical formula shows the simplest whole-number ratio of atoms in a compound, while the molecular formula shows the actual number of atoms in a molecule.

Question 2

Given the empirical formula $C_2H_7O$ and a molar mass of $90.08\ g/mol$, what is the molecular formula of the compound?

Accepted Answer

$C_4H_{14}O_2$

Question 3

A compound has an empirical formula of $NPC_2$ and a molar mass of $347.64\ g/mol$. What is its molecular formula?

Accepted Answer

$N_3P_3C_6$

Question 4

Which step is necessary to determine the molecular formula from the empirical formula and molar mass?

Accepted Answer

Multiply the empirical formula by the n-factor, which is the ratio of molar mass to empirical mass.

Question 5

Cortisol has a molar mass of $362.47\ g/mol$ and contains 69.6% carbon, 8.34% hydrogen, and 22.1% oxygen by mass. What is the first step in determining its molecular formula?

Accepted Answer

Calculate the empirical formula using the percent composition.

Question 6

A compound contains 72.2% C, 8.50% H, and the remainder is O. If 0.250 moles of the compound weighs 41.55 g, what is the molecular formula?

Accepted Answer

$C_{12}H_{16}O_4$

Question 7

If the empirical formula mass of a compound is $58\ g/mol$ and its molar mass is $174\ g/mol$, what is the n-factor?

Accepted Answer

$n = \frac{174}{58} = 3$

Question 8

Why is it important to use the empirical formula when determining the molecular formula of a compound?

Accepted Answer

The empirical formula gives the simplest ratio of elements, which is necessary to find the n-factor and thus the molecular formula.

Question 9

A compound has an empirical formula of $CH_2O$ and a molar mass of $180\ g/mol$. What is its molecular formula?

Accepted Answer

$C_6H_{12}O_6$

Question 10

Elemental analysis of a compound shows it contains 40% C, 6.7% H, and 53.3% O. If the molar mass is $90.08\ g/mol$, what is the molecular formula?

Accepted Answer

$C_3H_6O_3$

Question 11

Which of the following best describes the process for determining the molecular formula from percent composition and molar mass?

Accepted Answer

Calculate the empirical formula from percent composition, determine the empirical mass, divide the molar mass by the empirical mass to get n-factor, and multiply the empirical formula by n-factor.

Question 12

If a compound has an empirical formula of $C_2H_5$ and a molar mass of $58\ g/mol$, what is its molecular formula?

Accepted Answer

$C_4H_{10}$

Question 13

A sample of a compound contains 24.0 g of carbon, 4.0 g of hydrogen, and 32.0 g of oxygen. What is the empirical formula?

Accepted Answer

$CH_2O$

Question 14

Which of the following is NOT a correct step in determining the molecular formula?

Accepted Answer

Add the empirical formula to the molar mass.

Question 15

A compound has a molar mass of $120\ g/mol$ and an empirical formula of $CH_2$. What is its molecular formula?

Accepted Answer

$C_5H_{10}$

Question 16

If the empirical formula mass is $30\ g/mol$ and the molar mass is $90\ g/mol$, what is the molecular formula for a compound with an empirical formula of $CH_2O$?

Accepted Answer

$C_3H_6O_3$

Empirical and Molecular Formulas in GOB Chemistry

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