Q: Which sample contains the greatest number of atoms?

$$1\ \text{g} of $$carbon (C)$$\ (M=12.01\ \text{g/mol})$$

Q: A 16.2 g aluminum can contains how many aluminum atoms? (Molar mass of Al = $$26.98\ \text{g/mol}$$, Avogadro's number = $$6.022 \times 10$$^{23}$$ atoms/mol)

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

Q: How many molecules of $$\mathrm{CO}_2$$ are present in a 22.5 g sample of dry ice? (Molar mass of $$\mathrm{CO}_2 = 44.01\ \text{g/mol}$$, Avogadro's number = $$6.022 \times 10$$^{23}$$ molecules/mol)

$$3.08 \times 10$$^{23}$$ molecules

Q: A 3.64 g sample of water contains how many molecules of $$\mathrm{H}_2\mathrm{O}$$? (Molar mass = 18.02 g/mol, Avogadro's number = $$6.022 \times 10$$^{23}$$ molecules/mol)

$$1.22 \times 10$$^{23}$$ molecules

Q: A 25 g sample of HF contains slightly more than 1 mol of F atoms. Which of the following samples contains the greatest number of F atoms?

$$1.0\ \text{mol} of$$ $$\mathrm{F}_2$$

Question 1

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

Accepted Answer

Because atoms and molecules are so small and numerous that counting them individually is impractical.

Question 2

A sample contains $$3.0 	imes 10$$^{22}$$ atoms of gold (Au). How many moles of gold are present in the sample? (1$$\ 	ext{mol} = 6.022 	imes $$10^{23}$$ atoms)

Accepted Answer

$$0.050\ 	ext{mol}$$

Question 3

Which sample contains the greatest number of atoms?

Accepted Answer

$$1\ 	ext{g} of $$carbon (C)$$\ (M=12.01\ 	ext{g/mol})$$

Question 4

A 16.2 g aluminum can contains how many aluminum atoms? (Molar mass of Al = $$26.98\ 	ext{g/mol}$$, Avogadro's number = $$6.022 	imes 10$$^{23}$$ atoms/mol)

Accepted Answer

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

Question 5

Which of the following statements is TRUE regarding samples of different elements with the same mass?

Accepted Answer

They contain different numbers of atoms because the molar masses are different.

Question 6

How many molecules of $$\mathrm{CO}_2$$ are present in a 22.5 g sample of dry ice? (Molar mass of $$\mathrm{CO}_2 = 44.01\ 	ext{g/mol}$$, Avogadro's number = $$6.022 	imes 10$$^{23}$$ molecules/mol)

Accepted Answer

$$3.08 	imes 10$$^{23}$$ molecules

Question 7

A 5.8 g sample of sodium bicarbonate ($$\mathrm{NaHCO}_3) $$contains how many grams of oxygen? (Molar mass of $$\mathrm{NaHCO}_3 = 84.007\ 	ext{g/mol}$$, O = 16.00 g/mol)

Accepted Answer

$$3.3\ 	ext{g}$$

Question 8

Which of the following compounds has the highest mass percent of oxygen?

Accepted Answer

$$\mathrm{CrO}_2$$

Question 9

A sample of carvone ($$\mathrm{C}_{10}\mathrm{H}_{14}\mathrm{O}) $$weighs 55.4 g. How many grams of carbon does it contain? (Molar mass of carvone = 150.2 g/mol, C = 12.01 g/mol)

Accepted Answer

$$44.3\ 	ext{g}$$

Question 10

A compound is found to contain 24.5 g of nitrogen and 70.0 g of oxygen. What is its empirical formula? (N = 14.01 g/mol, O = 16.00 g/mol)

Accepted Answer

$$\mathrm{N}_2\mathrm{O}_5$$

Question 11

A 3.64 g sample of water contains how many molecules of $$\mathrm{H}_2\mathrm{O}$$? (Molar mass = 18.02 g/mol, Avogadro's number = $$6.022 	imes 10$$^{23}$$ molecules/mol)

Accepted Answer

$$1.22 	imes 10$$^{23}$$ molecules

Question 12

Which of the following best describes the process for determining the empirical formula of a compound from mass percent data?

Accepted Answer

Convert mass percent to grams, then to moles, write a pseudoformula, divide by the smallest subscript, and adjust to whole numbers.

Question 13

A compound has an empirical formula of $$\mathrm{CH}_2\mathrm{O}$$ and a molar mass of 180.2 g/mol. What is its molecular formula? (Empirical formula mass = 30.03 g/mol)

Accepted Answer

$$\mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_6$$

Question 14

If you have 12 moles of methane ($$\mathrm{CH}_4$$), how many moles of hydrogen atoms do you have?

Accepted Answer

$$48\ 	ext{mol}$$

Question 15

Which of the following best explains why a sample of $$1.0\ 	ext{mol} of$$ $$\mathrm{F}_2$$ contains $$2.0\ 	ext{mol} of $$fluorine atoms?

Accepted Answer

Each molecule of $$\mathrm{F}_2$$ contains two fluorine atoms, so $$1.0\ 	ext{mol} of$$ $$\mathrm{F}_2$$ contains $$2.0\ 	ext{mol} of F $$atoms.

Question 16

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

Accepted Answer

$$5.9\ 	ext{g}$$

Question 17

What is the mass percent of chlorine in $$\mathrm{C}_2\mathrm{Cl}_4\mathrm{F}_2$$? (C: 12.01 g/mol, Cl: 35.45 g/mol, F: 19.00 g/mol)

Accepted Answer

$$69.58\%$$

Question 18

A 25 g sample of HF contains slightly more than 1 mol of F atoms. Which of the following samples contains the greatest number of F atoms?

Accepted Answer

$$1.0\ 	ext{mol} of$$ $$\mathrm{F}_2$$

Question 19

Which of the following is a correct use of mass percent composition as a conversion factor?

Accepted Answer

To convert between grams of a compound and grams of an element using the percent by mass.

Question 20

A city fluoridates its water at $$0.7\ 	ext{mg/L}. If an $$adult drinks $$2.0\ 	ext{L} of $$water per day, how much fluoride do they consume daily?

Accepted Answer

$$1.4\ 	ext{mg}$$

Chapter 6: Chemical Composition and the Mole Concept

Study Guide - Practice Questions

Study Guide - Flashcards