$\text{moles} = \frac{\text{grams}}{\text{molar mass}}$

Question 1

Which of the following statements best explains why chemists use the mole as a counting unit for atoms?

Accepted Answer

Atoms are too small and numerous to count individually, so the mole allows chemists to count atoms by weighing them.

Question 2

What is the correct value for Avogadro's number?

Accepted Answer

$6.022 	imes 10^{23}$

Question 3

A sample contains $3.5$ moles of helium. How many helium atoms are present in the sample?

Accepted Answer

$2.1 	imes 10^{24}$ atoms

Question 4

How many moles of silver are present in a sample containing $1.1 	imes 10^{22}$ silver atoms?

Accepted Answer

$1.8 	imes 10^{-2}$ moles

Question 5

Which element contains the largest number of moles in a $10.0$ g sample: Na, C, Pb, Cu, or Ne?

Accepted Answer

Carbon (C)

Question 6

Calculate the number of moles of sulfur in $57.8$ g of sulfur. (Molar mass of S = $32.07$ g/mol)

Accepted Answer

$1.80$ moles

Question 7

How many aluminum atoms are present in an aluminum can with a mass of $16.2$ g? (Molar mass of Al = $26.98$ g/mol)

Accepted Answer

$3.61 	imes 10^{23}$ atoms

Question 8

What is the molar mass of carbon dioxide ($CO_2$)? (Atomic masses: C = $12.01$ amu, O = $16.00$ amu)

Accepted Answer

$44.01$ g/mol

Question 9

A sample contains $1.75$ moles of water ($H_2O$). What is the mass of this sample? (Molar mass of $H_2O = 18.02$ g/mol)

Accepted Answer

$31.5$ g

Question 10

What is the mass of $4.78 	imes 10^{22}$ molecules of $NO_2$? (Molar mass of $NO_2 = 46.01$ g/mol)

Accepted Answer

$3.65$ g

Question 11

How many moles of oxygen atoms are present in $1.7$ moles of $CaCO_3$?

Accepted Answer

$5.1$ moles

Question 12

A $15$ g sample of $NaCl$ contains how many grams of sodium? (Molar mass of $NaCl = 58.44$ g/mol, Na = $22.99$ g/mol)

Accepted Answer

$5.90$ g

Question 13

What is the mass percent of chromium in a sample if $0.358$ g of chromium reacts to form $0.523$ g of metal oxide?

Accepted Answer

$68.5\%$

Question 14

A compound is found to contain $40.00\%$ C, $6.729\%$ H, and $53.29\%$ O by mass. What is its empirical formula?

Accepted Answer

$CH_2O$

Question 15

The empirical formula of a compound is $CH_2O$ and its molar mass is $180.2$ g/mol. What is its molecular formula?

Accepted Answer

$C_6H_{12}O_6$

Question 16

Which of the following best describes the relationship between the empirical and molecular formulas of a compound?

Accepted Answer

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

Question 17

If a compound has a mass percent composition of $39\%$ sodium in sodium chloride, how many grams of sodium are present in $100$ g of sodium chloride?

Accepted Answer

$39$ g

Question 18

Which of the following is the correct formula to convert grams of a compound to moles?

Accepted Answer

$	ext{moles} = \frac{	ext{grams}}{	ext{molar mass}}$

Question 19

A $0.500$ g sample of a compound contains $0.200$ g of element X. What is the mass percent of X in the compound?

Accepted Answer

$40\%$

Question 20

Which of the following best explains why the mass of one mole of atoms differs for different elements?

Accepted Answer

Different elements have different atomic masses, so one mole of each element has a different mass.

Atoms, Moles, and Chemical Composition: Study Notes for Introductory Chemistry

Study Guide - Practice Questions