Q: Which of the following best describes a mole in chemistry?

A unit that counts 6.02 \times $$10^{23}$$ particles (atoms, molecules, or ions).

Q: How many atoms are present in 2.0 moles of aluminum (Al)?

$$2.0 \times 6.02 \times 10$$^{23}$$ = 1.20 \times 10$$^{24}$$ atoms

Q: What is the number of moles in $$1.8 \times 10$$^{24}$$ atoms of sulfur (S)?

$$\frac{1.8 \times 10$$^{24}$$}{6.02 \times 10$$^{23}$$} = 2.99$$ moles

Q: Aspirin has the formula $$C_9H_8O_4. $$How many moles of hydrogen atoms are in 0.5 moles of aspirin?

$$0.5 \text{ moles} \times \frac{8 \text{ moles H}}{1 \text{ mole } C_9H_8O_4} = 4$$ moles H

Q: What is the molar mass of $$C_2H_6O ($$ethanol)? (Atomic masses: C = 12.01, H = 1.01, O = 16.00)

$$2 \times 12.01 + 6 \times 1.01 + 1 \times 16.00 = 46.08 g/$$mol

Q: How many moles of water are in a 59.8 g sample of $$H_2O$$? (Molar mass of $$H_2O = 18.02 g/$$mol)

$$\frac{59.8 \text{ g}}{18.02 \text{ g/mol}} = 3.32$$ moles

Q: Calculate the molar mass of $$Li_2CO_3 ($$Atomic masses: Li = 6.94, C = 12.01, O = 16.00).

$$2 \times 6.94 + 12.01 + 3 \times 16.00 = 73.89 g/$$mol

Q: A chemist needs 0.25 moles of silver (Ag) for a reaction. What mass of silver should be weighed out? (Molar mass of Ag = 107.9 g/mol)

$$0.25 \text{ moles} \times 107.9 \text{ g/mol} = 27.0 g$$

Q: How many molecules are present in 18.02 g of water ($$H_2O$$)? (Molar mass of $$H_2O = 18.02 g/$$mol)

$$\frac{18.02}{18.02} \times 6.02 \times 10$$^{23}$$ = 6.02 \times 10$$^{23}$$ molecules

Question 1

Which of the following best describes a mole in chemistry?

Accepted Answer

A unit that counts 6.02 	imes $$10^{23}$$ particles (atoms, molecules, or ions).

Question 2

How many atoms are present in 2.0 moles of aluminum (Al)?

Accepted Answer

$$2.0 	imes 6.02 	imes 10$$^{23}$$ = 1.20 	imes 10$$^{24}$$ atoms

Question 3

What is the number of moles in $$1.8 	imes 10$$^{24}$$ atoms of sulfur (S)?

Accepted Answer

$$\frac{1.8 	imes 10$$^{24}$$}{6.02 	imes 10$$^{23}$$} = 2.99$$ moles

Question 4

Aspirin has the formula $$C_9H_8O_4. $$How many moles of hydrogen atoms are in 0.5 moles of aspirin?

Accepted Answer

$$0.5 	ext{ moles} 	imes \frac{8 	ext{ moles H}}{1 	ext{ mole } C_9H_8O_4} = 4$$ moles H

Question 5

What is the molar mass of $$C_2H_6O ($$ethanol)? (Atomic masses: C = 12.01, H = 1.01, O = 16.00)

Accepted Answer

$$2 	imes 12.01 + 6 	imes 1.01 + 1 	imes 16.00 = 46.08 g/$$mol

Question 6

How many moles of water are in a 59.8 g sample of $$H_2O$$? (Molar mass of $$H_2O = 18.02 g/$$mol)

Accepted Answer

$$\frac{59.8 	ext{ g}}{18.02 	ext{ g/mol}} = 3.32$$ moles

Question 7

Which of the following statements about Avogadro’s number is correct?

Accepted Answer

It is the number of particles in one mole of a substance.

Question 8

Calculate the molar mass of $$Li_2CO_3 ($$Atomic masses: Li = 6.94, C = 12.01, O = 16.00).

Accepted Answer

$$2 	imes 6.94 + 12.01 + 3 	imes 16.00 = 73.89 g/$$mol

Question 9

A chemist needs 0.25 moles of silver (Ag) for a reaction. What mass of silver should be weighed out? (Molar mass of Ag = 107.9 g/mol)

Accepted Answer

$$0.25 	ext{ moles} 	imes 107.9 	ext{ g/mol} = 27.0 g$$

Question 10

How many molecules are present in 18.02 g of water ($$H_2O$$)? (Molar mass of $$H_2O = 18.02 g/$$mol)

Accepted Answer

$$\frac{18.02}{18.02} 	imes 6.02 	imes 10$$^{23}$$ = 6.02 	imes 10$$^{23}$$ molecules

Question 11

A sample contains $$3.01 	imes 10$$^{23}$$ molecules of CO_2$. How many moles of CO_2$ are present?

Accepted Answer

$$\frac{3.01 	imes 10$$^{23}$$}{6.02 	imes 10$$^{23}$$} = 0.5$$ moles

Question 12

Which of the following is the correct conversion factor to find the number of moles of hydrogen in 1 mole of $$C_6H_{14}O$$?

Accepted Answer

$$\frac{14 	ext{ moles H}}{1 	ext{ mole } C_6H_{14}O}$$

Question 13

If you have 0.185 moles of $$C_6H_{14}O$$, how many moles of hydrogen atoms are present?

Accepted Answer

$$0.185 	imes 14 = 2.59$$ moles H

Question 14

Which of the following best explains why the mole is a useful unit in chemistry?

Accepted Answer

It allows chemists to count large numbers of particles using manageable numbers.

Question 15

A laboratory procedure requires 0.75 moles of $$NaCl. $$What mass of $$NaCl is $$needed? (Molar mass of $$NaCl = 58.44 g/$$mol)

Accepted Answer

$$0.75 	imes 58.44 = 43.83 g$$

Question 16

Which of the following is the correct sequence of steps to calculate the molar mass of a compound?

Accepted Answer

Obtain the molar mass of each element, multiply by the subscript, add the masses for each element.

The Mole and Calculating Molar Mass

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