Q: How many sodium atoms are present in 2.0 grams of sodium metal? (Atomic mass of Na = 22.99 g/mol)

$$2.0 \text{ g} \times \frac{1 \text{ mol}}{22.99 \text{ g}} \times 6.022 \times 10$$^{23}$$ \text{ atoms/mol} = 5.24 \times 10$$^{22}$$ atoms

Q: A sample contains $$1.1 \times 10$$^{22}$$ silver atoms. How many moles of silver does this represent?

$$\frac{1.1 \times 10$$^{22}$$}{6.022 \times 10$$^{23}$$} = 0.018$$ mol

Q: What is the molar mass of water ($$H_2O$$)? (Atomic masses: H = 1.01 g/mol, O = 16.00 g/mol)

$$2 \times 1.01 + 16.00 = 18.02 g/$$mol

Q: If you have 0.58 grams of diamond (pure carbon), how many moles of carbon do you have? (Atomic mass of C = 12.01 g/mol)

$$0.58 \text{ g} \times \frac{1 \text{ mol}}{12.01 \text{ g}} = 0.048$$ mol

Q: How many aluminum atoms are in an aluminum can with a mass of 16.2 grams? (Atomic mass of Al = 26.98 g/mol)

$$16.2 \text{ g} \times \frac{1 \text{ mol}}{26.98 \text{ g}} \times 6.022 \times 10$$^{23}$$ = 3.62 \times 10$$^{23}$$ atoms

Q: A compound has a mass percent composition of 39% sodium by mass. How many grams of sodium are in 15 grams of sodium chloride ($$NaCl$$)?

$$15 \text{ g} \times \frac{39}{100} = 5.85 g Na$$

Q: What is the mass percent of chlorine in Freon-114 ($$C_2Cl_4F_2$$)? (Atomic masses: C = 12.01 g/mol, Cl = 35.45 g/mol, F = 19.00 g/mol)

$$\frac{4 \times 35.45}{2 \times 12.01 + 4 \times 35.45 + 2 \times 19.00} \times 100 = 59.6\%$$

Q: How many moles of oxygen atoms are present in 1.7 moles of CaCO$$_3$$?

$$1.7 \text{ mol CaCO}_3 \times \frac{3 \text{ mol O}}{1 \text{ mol CaCO}_3} = 5.1$$ mol O

Question 1

Which statement best describes the mole concept in chemistry?

Accepted Answer

A mole is a specific number of particles, defined as $$6.022 	imes 10$$^{23}$$, that allows chemists to count atoms or molecules by weighing them.

Question 2

How many sodium atoms are present in 2.0 grams of sodium metal? (Atomic mass of Na = 22.99 g/mol)

Accepted Answer

$$2.0 	ext{ g} 	imes \frac{1 	ext{ mol}}{22.99 	ext{ g}} 	imes 6.022 	imes 10$$^{23}$$ 	ext{ atoms/mol} = 5.24 	imes 10$$^{22}$$ atoms

Question 3

A sample contains $$1.1 	imes 10$$^{22}$$ silver atoms. How many moles of silver does this represent?

Accepted Answer

$$\frac{1.1 	imes 10$$^{22}$$}{6.022 	imes 10$$^{23}$$} = 0.018$$ mol

Question 4

What is the molar mass of water ($$H_2O$$)? (Atomic masses: H = 1.01 g/mol, O = 16.00 g/mol)

Accepted Answer

$$2 	imes 1.01 + 16.00 = 18.02 g/$$mol

Question 5

If you have 0.58 grams of diamond (pure carbon), how many moles of carbon do you have? (Atomic mass of C = 12.01 g/mol)

Accepted Answer

$$0.58 	ext{ g} 	imes \frac{1 	ext{ mol}}{12.01 	ext{ g}} = 0.048$$ mol

Question 6

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

Accepted Answer

$$16.2 	ext{ g} 	imes \frac{1 	ext{ mol}}{26.98 	ext{ g}} 	imes 6.022 	imes 10$$^{23}$$ = 3.62 	imes 10$$^{23}$$ atoms

Question 7

A compound has a mass percent composition of 39% sodium by mass. How many grams of sodium are in 15 grams of sodium chloride ($$NaCl$$)?

Accepted Answer

$$15 	ext{ g} 	imes \frac{39}{100} = 5.85 g Na$$

Question 8

What is the mass percent of chlorine in Freon-114 ($$C_2Cl_4F_2$$)? (Atomic masses: C = 12.01 g/mol, Cl = 35.45 g/mol, F = 19.00 g/mol)

Accepted Answer

$$\frac{4 	imes 35.45}{2 	imes 12.01 + 4 	imes 35.45 + 2 	imes 19.00} 	imes 100 = 59.6\%$$

Question 9

A 3.24-gram sample of titanium reacts with oxygen to form 5.40 grams of titanium oxide. What is the empirical formula of the oxide? (Atomic masses: Ti = 47.87 g/mol, O = 16.00 g/mol)

Accepted Answer

TiO

Question 10

If the empirical formula of a compound is CH$$_2O $$and its molar mass is 180.2 g/mol, what is its molecular formula? (Empirical formula mass = 30.03 g/mol)

Accepted Answer

C$$_6H$_{12}O$_6$$

Question 11

How many moles of oxygen atoms are present in 1.7 moles of CaCO$$_3$$?

Accepted Answer

$$1.7 	ext{ mol CaCO}_3 	imes \frac{3 	ext{ mol O}}{1 	ext{ mol CaCO}_3} = 5.1$$ mol O

Question 12

A water sample is decomposed to produce 3.0 g of hydrogen and 24 g of oxygen. What is the empirical formula of water based on these data? (Atomic masses: H = 1.01 g/mol, O = 16.00 g/mol)

Accepted Answer

H$$_2O$$

Question 13

Which of the following best explains why the mass of sodium chloride consumed is not the same as the mass of sodium consumed?

Accepted Answer

Sodium chloride contains both sodium and chlorine, and their atomic masses are different.

Question 14

How many molecules are present in 4.78 $$	imes 10$^{24}$$ molecules of NO$$_2$$?

Accepted Answer

4.78 $$	imes 10$^{24}$$ molecules

Question 15

If a compound contains 12.0 g of carbon, 2.0 g of hydrogen, and 16.0 g of oxygen, what is the empirical formula? (Atomic masses: C = 12.01 g/mol, H = 1.01 g/mol, O = 16.00 g/mol)

Accepted Answer

CH$$_2O$$

Question 16

Which of the following is true about the relationship between atomic mass and molar mass?

Accepted Answer

The molar mass of an element in grams per mole is numerically equal to its atomic mass in atomic mass units.

Question 17

A chemist wants to fluoridate 1500 L of water at a level of 1.0 mg/L using sodium fluoride (NaF). What mass of NaF should be added? (Molar mass of NaF = 41.99 g/mol)

Accepted Answer

$$1500 	ext{ L} 	imes 1.0 	ext{ mg/L} = 1500 	ext{ mg} = 1.5 	ext{ g}$$ NaF

Chemical Composition: The Mole, Molar Mass, and Chemical Formulas

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