Question 1

Which of the following best describes the empirical formula of a compound?

Accepted Answer

The formula that gives the simplest whole-number ratio of atoms of each element in a compound.

Question 2

A compound contains 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen by mass. What is the empirical formula of this compound?

Accepted Answer

$$\mathrm{CH_2O}$$

Question 3

If a compound has a molecular formula of $$\mathrm{C_6H_{12}O_6$}$$, what is its empirical formula?

Accepted Answer

$$\mathrm{CH_2O}$$

Question 4

A sample contains 2.2 g of Na, 3.6 g of Cl, and 7.8 g of O. What is the empirical formula of the compound?

Accepted Answer

$$\mathrm{$$NaClO_2$$}$$

Question 5

Which step is NOT part of the process for determining the empirical formula from percent composition?

Accepted Answer

Add the masses of all elements to get the molecular formula.

Question 6

A compound is found to contain 52.2% carbon, 13.0% hydrogen, and 34.8% oxygen by mass. What is the empirical formula?

Accepted Answer

$$\mathrm{C_2H_6O}$$

Question 7

Which of the following statements is TRUE regarding empirical and molecular formulas?

Accepted Answer

The empirical formula may be different from the molecular formula if the compound is not in its simplest ratio.

Question 8

A compound contains only carbon, hydrogen, and oxygen. It is found to contain 48.6% C, 8.1% H, and 43.2% O by mass. What is the empirical formula?

Accepted Answer

$$\mathrm{C_2H_4O}$$

Question 9

Why is it necessary to divide the number of moles of each element by the smallest number of moles when determining the empirical formula?

Accepted Answer

To obtain the simplest whole-number ratio of atoms.

Question 10

A compound contains 1.71 x $$10^{24}$$ hydrogen atoms and 9.00 g of the compound contains 52.0% chlorine by mass. What is the empirical formula?

Accepted Answer

$$\mathrm{CH_2Cl_2}$$

Question 11

Which of the following is a correct step in calculating the empirical formula from mass data?

Accepted Answer

Convert the mass of each element to moles using the molar mass.

Question 12

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

Accepted Answer

$$\mathrm{C_6H_{12}O_6$}$$

Question 13

Which of the following best explains why empirical formulas are important in chemistry?

Accepted Answer

They provide the simplest ratio of elements, which is useful for identifying unknown compounds.

Question 14

A compound is analyzed and found to contain 24.3% magnesium, 32.0% sulfur, and 43.7% oxygen. What is the empirical formula?

Accepted Answer

$$\mathrm{$$MgSO_3$$}$$

Question 15

Which of the following is a reason why the empirical formula might differ from the molecular formula?

Accepted Answer

The molecular formula is a whole-number multiple of the empirical formula.

Empirical and Molecular Formulas: Concepts and Calculations

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