Q: A chemist has 50.0 g of magnesium. How many magnesium atoms are present in this sample? (Molar mass of Mg = 24.305 g/mol, Avogadro's number $$= 6.022 \times 10$$^{23}$$)

$$3.717 \times 10$$^{24}$$ atoms

Q: Which conversion factor would you use to convert from moles of atoms to number of atoms?

$$6.022 \times 10$$^{23}$$ \text{ atoms} / 1 \text{ mol atoms}$$

Q: A sample contains 12.00 grams of carbon. How many carbon atoms are present?

$$6.022 \times 10$$^{23}$$ atoms

Q: Which statement is true about the mole concept?

A mole is a counting unit that represents $$6.022 \times 10$$^{23}$$ particles.

Q: If you have 1 mole of helium atoms, how many atoms do you have?

$$6.022 \times 10$$^{23}$$ atoms

Q: Which equation correctly relates mass, molar mass, and number of moles?

$$\text{mass} = \text{moles} \times \text{molar mass}$$

Q: How many aluminum atoms are there in 9.0 g of aluminum? (Molar mass of Al = 26.98 g/mol, Avogadro's number $$= 6.022 \times 10$$^{23}$$)

$$2.01 \times 10$$^{23}$$ atoms

Question 1

Which statement best describes the relationship between atomic mass unit (amu) and molar mass in grams for an element?

Accepted Answer

The atomic mass in amu for one atom equals the molar mass in grams for one mole of atoms.

Question 2

A chemist has 50.0 g of magnesium. How many magnesium atoms are present in this sample? (Molar mass of Mg = 24.305 g/mol, Avogadro's number $$= 6.022 	imes 10$$^{23}$$)

Accepted Answer

$$3.717 	imes 10$$^{24}$$ atoms

Question 3

What is the significance of Avogadro’s number ($$6.022 	imes 10$$^{23}$$)?

Accepted Answer

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

Question 4

If you have 1000 atoms of magnesium, what is their mass? (Molar mass of Mg = 24.305 g/mol, Avogadro's number $$= 6.022 	imes 10$$^{23}$$)

Accepted Answer

$$4.04 	imes 10$$^{-20}$$ g

Question 5

Which conversion factor would you use to convert from moles of atoms to number of atoms?

Accepted Answer

$$6.022 	imes 10$$^{23}$$ 	ext{ atoms} / 1 	ext{ mol atoms}$$

Question 6

A sample contains 12.00 grams of carbon. How many carbon atoms are present?

Accepted Answer

$$6.022 	imes 10$$^{23}$$ atoms

Question 7

What is the molar mass of gold (Au)?

Accepted Answer

197 g

Question 8

How many moles of iron are contained in 6.09 g of iron? (Molar mass of Fe = 55.85 g/mol)

Accepted Answer

$$0.109$$ mol

Question 9

Which statement is true about the mole concept?

Accepted Answer

A mole is a counting unit that represents $$6.022 	imes 10$$^{23}$$ particles.

Question 10

What is the molecular weight of water (H$$_2O) in $$amu?

Accepted Answer

18.0 amu

Question 11

How many grams of hydrogen are there in 100.0 g of water? (Molar mass of H$$_2O = 18.02 g/$$mol, 2 mol H per mol H$$_2O$$, molar mass of H = 1.008 g/mol)

Accepted Answer

11.2 g

Question 12

Which of the following best explains why a small mass of a substance contains a huge number of particles?

Accepted Answer

Atoms and molecules are extremely small, so even a few grams contain many particles.

Question 13

If you have 1 mole of helium atoms, how many atoms do you have?

Accepted Answer

$$6.022 	imes 10$$^{23}$$ atoms

Question 14

Which of the following is the correct molar mass for carbon dioxide (CO$$_2$$)? (C = 12.01 g/mol, O = 16.00 g/mol)

Accepted Answer

44.01 g/mol

Question 15

A laboratory sample contains $$3.00 	imes 10$$^{24}$$ molecules of water. How many moles of water does this sample contain?

Accepted Answer

$$4.98$$ mol

Question 16

Which equation correctly relates mass, molar mass, and number of moles?

Accepted Answer

$$	ext{mass} = 	ext{moles} 	imes 	ext{molar mass}$$

Question 17

How many aluminum atoms are there in 9.0 g of aluminum? (Molar mass of Al = 26.98 g/mol, Avogadro's number $$= 6.022 	imes 10$$^{23}$$)

Accepted Answer

$$2.01 	imes 10$$^{23}$$ atoms

Question 18

Which of the following is true about molar mass?

Accepted Answer

Molar mass is the mass of one mole of particles in grams.

Question 19

A student wants to convert 18.0 g of water to number of molecules. Which sequence of conversion factors should they use?

Accepted Answer

$$\frac{1 	ext{ mol H}_2	ext{O}}{18.0 	ext{ g H}_2	ext{O}}$$ then $$\frac{6.022 	imes 10$$^{23}$$ 	ext{ molecules}}{1 	ext{ mol H}_2	ext{O}}$$

Counting Particles by Weighing Them: The Mole, Avogadro’s Number, and Molar Mass

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