Q: A sample contains $$50.0\ \mathrm{g} of $$magnesium ($$\mathrm{Mg}). $$How many magnesium atoms are present in the sample? ($$\mathrm{Molar\ mass\ of\ Mg} = 24.305\ \mathrm{g/mol})$$

$$3.71 \times 10$$^{24}$$ atoms

Q: What is Avogadro's number and what does it represent?

$$6.022 \times 10$$^{23}$$; the number of atoms in 12.00$$\ \mathrm{g}$$ of carbon-12

Q: If you have $$1000$$ atoms of magnesium ($$\mathrm{Mg}$$), what is their total mass? ($$\mathrm{Molar\ mass\ of\ Mg} = 24.305\ \mathrm{g/mol})$$

$$4.04 \times 10$$^{-20}$$\ \mathrm{g}$$

Q: A laboratory sample contains $$18.0\ \mathrm{g} of $$water. How many molecules of water are present in the sample? ($$\mathrm{Molar\ mass\ of\ H_2O} = 18.0\ \mathrm{g/mol})$$

$$6.02 \times 10$$^{23}$$ molecules

Q: If you have $$0.500\ \mathrm{mol} of $$aluminum ($$\mathrm{Al}$$), how many atoms of aluminum do you have?

$$3.01 \times 10$$^{23}$$ atoms

Question 1

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

Accepted Answer

The atomic mass in amu of a single atom is numerically equal to the molar mass in grams of one mole of those atoms.

Question 2

A sample contains $$50.0\ \mathrm{g} of $$magnesium ($$\mathrm{Mg}). $$How many magnesium atoms are present in the sample? ($$\mathrm{Molar\ mass\ of\ Mg} = 24.305\ \mathrm{g/mol})$$

Accepted Answer

$$3.71 	imes 10$$^{24}$$ atoms

Question 3

What is Avogadro's number and what does it represent?

Accepted Answer

$$6.022 	imes 10$$^{23}$$; the number of atoms in 12.00$$\ \mathrm{g}$$ of carbon-12

Question 4

If you have $$1000$$ atoms of magnesium ($$\mathrm{Mg}$$), what is their total mass? ($$\mathrm{Molar\ mass\ of\ Mg} = 24.305\ \mathrm{g/mol})$$

Accepted Answer

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

Question 5

Which of the following statements is TRUE regarding the mole concept?

Accepted Answer

A mole is a counting unit that allows chemists to relate the mass of a substance to the number of particles it contains.

Question 6

How many grams of hydrogen are present in $$100.0\ \mathrm{g} of $$water ($$\mathrm{H_2O}$$)? ($$\mathrm{Molar\ mass\ of\ H_2O} = 18.02\ \mathrm{g/mol}$$, $$\mathrm{Molar\ mass\ of\ H} = 1.008\ \mathrm{g/mol})$$

Accepted Answer

$$11.2\ \mathrm{g}$$

Question 7

What is the molar mass of gold ($$\mathrm{Au}$$)?

Accepted Answer

$$197\ \mathrm{g/mol}$$

Question 8

A chemist has $$6.09\ \mathrm{g} of $$iron ($$\mathrm{Fe}). If $$the molar mass of iron is $$55.85\ \mathrm{g/mol}$$, how many moles of iron are present?

Accepted Answer

$$0.109$$ moles

Question 9

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 small mass contains a very large number of them.

Question 10

What is the molecular weight of ethanol ($$\mathrm{C_2H_6O}) in $$amu?

Accepted Answer

$$46.08\ \mathrm{amu}$$

Question 11

A laboratory sample contains $$18.0\ \mathrm{g} of $$water. How many molecules of water are present in the sample? ($$\mathrm{Molar\ mass\ of\ H_2O} = 18.0\ \mathrm{g/mol})$$

Accepted Answer

$$6.02 	imes 10$$^{23}$$ molecules

Question 12

If you have $$0.500\ \mathrm{mol} of $$aluminum ($$\mathrm{Al}$$), how many atoms of aluminum do you have?

Accepted Answer

$$3.01 	imes 10$$^{23}$$ atoms

Question 13

Which conversion factor would you use to convert from grams of a substance to number of particles?

Accepted Answer

$$\frac{1\ \mathrm{mol}}{\mathrm{molar\ mass\ (g)}}$$ then $$\frac{6.022 	imes 10$$^{23}$$\ \mathrm{particles}}{1\ \mathrm{mol}}$$

Question 14

A student claims that $$1\ \mathrm{mol} of $$helium ($$\mathrm{He}) $$weighs $$4.00\ \mathrm{amu}. $$What is wrong with this statement?

Accepted Answer

The mass of $$1\ \mathrm{mol} of He $$should be in grams, not amu.

Question 15

How many moles of water are present in $$36.04\ \mathrm{g} of $$water? ($$\mathrm{Molar\ mass\ of\ H_2O} = 18.02\ \mathrm{g/mol})$$

Accepted Answer

$$2.00$$ moles

Question 16

Which of the following is the correct definition of molar mass?

Accepted Answer

The mass in grams of one mole of a substance.

Question 17

A sample contains $$1.00\ \mathrm{g} of $$carbon. How many atoms of carbon are present? ($$\mathrm{Molar\ mass\ of\ C} = 12.00\ \mathrm{g/mol})$$

Accepted Answer

$$5.02 	imes 10$$^{22}$$ atoms

Question 18

Which of the following best describes the significance of Avogadro's number in chemistry?

Accepted Answer

It allows chemists to count atoms and molecules by weighing macroscopic amounts of material.

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

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