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

A mole is a specific number, $$6.022 \times 10$$^{23}$$, of particles such as atoms, molecules, or ions.

Q: How many atoms are present in $$2.00$$ moles of magnesium ($$Mg$$)?

$$1.20 \times 10$$^{24}$$ atoms$$\ (2.00\ \text{mol} \times 6.022 \times $$10^{23}$$\ \text{atoms/mol})$$

Q: How many grams of $$H_2O$$ are present in $$0.250$$ moles of water?

$$4.51 g$\ (0.250\ \text{mol} \times 18.02\ \text{g/mol})$$

Q: A can contains $$16.2$$ grams of aluminum ($$Al). $$How many atoms of aluminum are in the can? (Molar mass of $$Al = 26.98 g/$$mol)

$$3.62 \times 10$$^{23}$$ atoms

Q: How many moles of oxygen atoms are in $$2.0$$ moles of $$CO_2$$?

$$4.0$$ mol$$\ (2.0\ \text{mol}\ CO_2$ \times 2\ \text{mol O}/1\ \text{mol}\ CO_2$)$$

Q: How many grams of nitrogen are in $$10.0$$ grams of $$NH_3 ($$ammonia)? (Molar mass of $$NH_3 = 17.03$ g/mol, N = 14.01$ g/mol)

$$8.23 g$\ (10.0\ \text{g}\ NH_3$ \times \frac{1\ \text{mol}\ NH_3$}{17.03\ \text{g}} \times \frac{1\ \text{mol}\ N}{1\ \text{mol}\ NH_3$} \times 14.01\ \text{g})$$

Q: Which conversion factor would you use to convert from grams of $$C_6H_{12}O_6$ (glucose) to moles of C_6H$$_{12}$$O_6$$?

$$\frac{1\ \text{mol}\ C_6H_{12}O_6$}{180.16\ \text{g}\ C_6H_{12}O_6$}$$

Question 1

Which of the following statements best describes the mole in chemistry?

Accepted Answer

A mole is a specific number, $$6.022 	imes 10$$^{23}$$, of particles such as atoms, molecules, or ions.

Question 2

How many atoms are present in $$2.00$$ moles of magnesium ($$Mg$$)?

Accepted Answer

$$1.20 	imes 10$$^{24}$$ atoms$$\ (2.00\ 	ext{mol} 	imes 6.022 	imes $$10^{23}$$\ 	ext{atoms/mol})$$

Question 3

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

Accepted Answer

$$0.500$$ mol

Question 4

What is the molar mass of $$NaCl ($$sodium chloride)?

Accepted Answer

$$58.44 g/$$mol$$\ (22.99\ +\ 35.45)$$

Question 5

How many grams of $$H_2O$$ are present in $$0.250$$ moles of water?

Accepted Answer

$$4.51 g$\ (0.250\ 	ext{mol} 	imes 18.02\ 	ext{g/mol})$$

Question 6

A can contains $$16.2$$ grams of aluminum ($$Al). $$How many atoms of aluminum are in the can? (Molar mass of $$Al = 26.98 g/$$mol)

Accepted Answer

$$3.62 	imes 10$$^{23}$$ atoms

Question 7

How many moles of oxygen atoms are in $$2.0$$ moles of $$CO_2$$?

Accepted Answer

$$4.0$$ mol$$\ (2.0\ 	ext{mol}\ CO_2$ 	imes 2\ 	ext{mol O}/1\ 	ext{mol}\ CO_2$)$$

Question 8

A patient is prescribed a daily sodium intake of less than $$2.3$$ grams. What is the maximum mass of $$NaCl ($$table salt) they can consume per day? ($$Na$$ atomic mass = $$22.99 g/$$mol, $$Cl$$ atomic mass = $$35.45 g/$$mol)

Accepted Answer

$$5.8 g$$

Question 9

What is the empirical formula of a compound containing $$40.0\%$$ carbon, $$6.7\%$$ hydrogen, and $$53.3\%$$ oxygen by mass?

Accepted Answer

$$CH_2O$$

Question 10

How many grams of nitrogen are in $$10.0$$ grams of $$NH_3 ($$ammonia)? (Molar mass of $$NH_3 = 17.03$ g/mol, N = 14.01$ g/mol)

Accepted Answer

$$8.23 g$\ (10.0\ 	ext{g}\ NH_3$ 	imes \frac{1\ 	ext{mol}\ NH_3$}{17.03\ 	ext{g}} 	imes \frac{1\ 	ext{mol}\ N}{1\ 	ext{mol}\ NH_3$} 	imes 14.01\ 	ext{g})$$

Question 11

Which of the following best explains why the mass of one mole of sulfur is greater than the mass of one mole of carbon?

Accepted Answer

Sulfur atoms are heavier than carbon atoms.

Question 12

A sample contains $$4.78 	imes 10$$^{24}$$ molecules of NO_2$. What is the mass of this sample? (Molar mass of NO_2$ = 46.01 g/$$mol)

Accepted Answer

$$365 g$$

Question 13

Which conversion factor would you use to convert from grams of $$C_6H_{12}O_6$ (glucose) to moles of C_6H$$_{12}$$O_6$$?

Accepted Answer

$$\frac{1\ 	ext{mol}\ C_6H_{12}O_6$}{180.16\ 	ext{g}\ C_6H_{12}O_6$}$$

Question 14

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

Accepted Answer

$$0.048$$ mol

Question 15

Which of the following is true about the relationship between the chemical formula and the mass of a compound?

Accepted Answer

The chemical formula provides the ratio of atoms, which, combined with atomic masses, allows calculation of the compound's mass.

Question 16

How many moles of $$O$$ atoms are in $$1.7$$ moles of $$CaCO_3$$?

Accepted Answer

$$5.1$$ mol$$\ (1.7\ 	ext{mol}\ $$CaCO_3$$ 	imes 3\ 	ext{mol}\ O/1\ 	ext{mol}\ $$CaCO_3$$)$$

Question 17

A hardware store sells nails by the pound. If a dozen nails weigh $$0.150 lb $$and a customer buys $$2.60 lb$$, how many nails did the customer buy?

Accepted Answer

$$208$$ nails

Question 18

Which of the following best describes why chemists use the mole instead of counting individual atoms?

Accepted Answer

Atoms are too small and numerous to count individually, so the mole provides a practical counting unit.

Question 19

Which of the following is the correct sequence of steps to find the number of atoms in a given mass of an element?

Accepted Answer

Convert grams to moles, then moles to atoms using Avogadro's number.

Chapter 6: Chemical Composition – The Mole, Molar Mass, and Chemical Formulas

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