Q: A sample contains $$3.5\ \mathrm{mol} of $$helium. How many helium atoms are present? ($$N_A = 6.022 \times 10$$^{23}$$\ \mathrm{mol}^{-1})$$

$$2.11 \times 10$$^{24}$$ atoms

Q: How many molecules are in $$36.0\ \mathrm{g} of $$water? (Molar mass of $$\mathrm{H_2O} = 18.02\ \mathrm{g/mol}$$, $$N_A = 6.022 \times 10$$^{23}$$)

$$1.20 \times 10$$^{24}$$ molecules

Q: A sample contains $$1.00\ \mathrm{mol} of$$ $$\mathrm{C_6H_{12}O_6$}. $$How many oxygen atoms are present?

$$6.022 \times 10$$^{24}$$ atoms

Question 1

A nutrition label states that a serving of soup contains 1.5 g of sodium chloride (NaCl). How many grams of sodium (Na) are in this serving? (Atomic masses: Na = 22.99, Cl = 35.45)

Accepted Answer

$$0.60\ \mathrm{g}$$

Question 2

Which of the following statements best describes Avogadro’s number?

Accepted Answer

It is the number of atoms in exactly 12 grams of carbon-12.

Question 3

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

Accepted Answer

$$0.601\ \mathrm{mol}$$

Question 4

A sample contains $$3.5\ \mathrm{mol} of $$helium. How many helium atoms are present? ($$N_A = 6.022 	imes 10$$^{23}$$\ \mathrm{mol}^{-1})$$

Accepted Answer

$$2.11 	imes 10$$^{24}$$ atoms

Question 5

What is the mass of $$1.75\ \mathrm{mol} of $$water ($$\mathrm{H_2O}$$)? (Molar mass of $$\mathrm{H_2O} = 18.02\ \mathrm{g/mol})$$

Accepted Answer

$$31.5\ \mathrm{g}$$

Question 6

How many oxygen atoms are in $$1.7\ \mathrm{mol} of$$ $$\mathrm{$$CaCO_3$$}$$?

Accepted Answer

$$5.1\ \mathrm{mol}$$

Question 7

A chemist has $$0.58\ \mathrm{g} of $$diamond (pure carbon). How many moles of carbon does this represent? (Molar mass of C = $$12.01\ \mathrm{g/mol})$$

Accepted Answer

$$0.048\ \mathrm{mol}$$

Question 8

How many molecules are in $$36.0\ \mathrm{g} of $$water? (Molar mass of $$\mathrm{H_2O} = 18.02\ \mathrm{g/mol}$$, $$N_A = 6.022 	imes 10$$^{23}$$)

Accepted Answer

$$1.20 	imes 10$$^{24}$$ molecules

Question 9

If a sample contains $$1.204 	imes 10$$^{24}$$ molecules of $$\mathrm{$$CO_2$$}$$, what is the mass of the sample? (Molar mass of $$\mathrm{$$CO_2$$} = 44.01\ \mathrm{g/mol}$$, N_A = 6.022$$ 	imes $$10^{23})$$

Accepted Answer

$$44.0\ \mathrm{g}$$

Question 10

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

Accepted Answer

$$5.90\ \mathrm{g}$$

Question 11

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 12

How many moles of chlorine atoms are in $$2.0\ \mathrm{mol} of$$ $$\mathrm{$$CCl_4$$}$$?

Accepted Answer

$$8.0\ \mathrm{mol}$$

Question 13

A sample contains $$4.50\ \mathrm{mol} of$$ $$\mathrm{H_2O}. $$How many moles of hydrogen atoms are present?

Accepted Answer

$$9.00\ \mathrm{mol}$$

Question 14

Which of the following is the correct molar mass for $$\mathrm{Al_2$(SO_4$)_3}$$? (Al = 26.98, S = 32.07, O = 16.00)

Accepted Answer

$$342.14\ \mathrm{g/mol}$$

Question 15

A chemist wants to know how much iron is in a 10.0 g sample of iron(III) oxide ($$\mathrm{Fe_2O_3}). ($$Molar mass $$\mathrm{Fe_2O_3} = 159.7 g/$$mol, Fe = 55.85 g/mol)

Accepted Answer

$$6.99\ \mathrm{g}$$

Question 16

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

Accepted Answer

Atoms and molecules are too small and numerous to count individually.

Question 17

If you have $$0.25\ \mathrm{mol} of$$ $$\mathrm{Na_2SO_4}$$, how many moles of sodium ions are present?

Accepted Answer

$$0.50\ \mathrm{mol}$$

Question 18

A sample contains $$1.00\ \mathrm{mol} of$$ $$\mathrm{C_6H_{12}O_6$}. $$How many oxygen atoms are present?

Accepted Answer

$$6.022 	imes 10$$^{24}$$ atoms

Question 19

Which of the following is true about the molar mass of an element?

Accepted Answer

It is numerically equal to the atomic mass in amu, but expressed in grams per mole.

Chapter 6: Chemical Composition – Study Notes

Study Guide - Practice Questions

Study Guide - Flashcards