Q: Which of the following statements about Avogadro's number is correct?

Avogadro's number is $$6.022 \times 10$$^{23}$$ and represents the number of particles in one mole.

Q: If you have 3.0 moles of water ($$H_2O$$), how many molecules of water do you have?

$$3.0 \times 6.022 \times 10$$^{23}$$ = 1.81 \times 10$$^{24}$$ molecules

Q: A chemist needs to prepare 0.5 moles of sodium chloride ($$NaCl). $$What mass of $$NaCl is $$required? (Molar mass of $$NaCl = 58.44 g/$$mol)

$$0.5 \times 58.44 = 29.22$$ grams

Q: A sample contains $$1.204 \times 10$$^{24}$$ atoms of magnesium (Mg$). How many moles of magnesium are present?

$$\frac{1.204 \times 10$$^{24}$$}{6.022 \times 10$$^{23}$$} = 2.00$$ moles

Q: A medical laboratory needs 0.25 moles of glucose ($$C_6H_{12}O_6$) for a test. What mass of glucose should be weighed out? (Molar mass of C_6H$$_{12}$$O_6 = 180.16 g/$$mol)

$$0.25 \times 180.16 = 45.04$$ grams

Q: A reaction requires 0.75 moles of calcium chloride ($$CaCl_2). $$What is the mass needed? (Molar mass of $$CaCl_2 = 110.98 g/$$mol)

$$0.75 \times 110.98 = 83.24$$ grams

Question 1

Which of the following best describes the relationship between grams and moles for a given substance?

Accepted Answer

The number of grams is equal to the number of moles multiplied by the molar mass.

Question 2

A student has 24.0 grams of carbon (C). What is the number of moles present? (Atomic mass of C = 12.01 g/mol)

Accepted Answer

$$\frac{24.0}{12.01} = 2.00$$ moles

Question 3

Which of the following statements about Avogadro's number is correct?

Accepted Answer

Avogadro's number is $$6.022 	imes 10$$^{23}$$ and represents the number of particles in one mole.

Question 4

If you have 3.0 moles of water ($$H_2O$$), how many molecules of water do you have?

Accepted Answer

$$3.0 	imes 6.022 	imes 10$$^{23}$$ = 1.81 	imes 10$$^{24}$$ molecules

Question 5

A chemist needs to prepare 0.5 moles of sodium chloride ($$NaCl). $$What mass of $$NaCl is $$required? (Molar mass of $$NaCl = 58.44 g/$$mol)

Accepted Answer

$$0.5 	imes 58.44 = 29.22$$ grams

Question 6

Which of the following best explains why the concept of the mole is important in chemistry?

Accepted Answer

It allows chemists to count atoms and molecules by weighing them.

Question 7

A sample contains $$1.204 	imes 10$$^{24}$$ atoms of magnesium (Mg$). How many moles of magnesium are present?

Accepted Answer

$$\frac{1.204 	imes 10$$^{24}$$}{6.022 	imes 10$$^{23}$$} = 2.00$$ moles

Question 8

Which calculation would you use to convert 10.0 grams of oxygen gas ($$O_2) to $$moles? (Molar mass of $$O_2 = 32.00 g/$$mol)

Accepted Answer

$$\frac{10.0}{32.00}$$

Question 9

A medical laboratory needs 0.25 moles of glucose ($$C_6H_{12}O_6$) for a test. What mass of glucose should be weighed out? (Molar mass of C_6H$$_{12}$$O_6 = 180.16 g/$$mol)

Accepted Answer

$$0.25 	imes 180.16 = 45.04$$ grams

Question 10

Which of the following is the correct way to convert from moles to number of particles (atoms, molecules, or ions)?

Accepted Answer

Multiply the number of moles by Avogadro's number.

Question 11

A reaction requires 0.75 moles of calcium chloride ($$CaCl_2). $$What is the mass needed? (Molar mass of $$CaCl_2 = 110.98 g/$$mol)

Accepted Answer

$$0.75 	imes 110.98 = 83.24$$ grams

Question 12

Which of the following best describes the term 'molar mass'?

Accepted Answer

The mass of one mole of a substance, expressed in grams per mole.

Question 13

A sample of iron ($$Fe) $$weighs 55.85 grams. How many moles of iron are present? (Atomic mass of $$Fe = 55.85 g/$$mol)

Accepted Answer

$$\frac{55.85}{55.85} = 1.00$$ mole

Question 14

Which of the following is a correct real-life application of the mole concept?

Accepted Answer

Determining the amount of medication to administer based on the number of molecules required for efficacy.

Question 15

A chemist has 0.10 moles of sulfuric acid ($$H_2SO_4). $$How many molecules of $$H_2SO_4$$ does this represent?

Accepted Answer

$$0.10 	imes 6.022 	imes 10$$^{23}$$ = 6.022 	imes 10$$^{22}$$ molecules

Question 16

Which of the following best explains why the atomic mass of chlorine is not a whole number?

Accepted Answer

Because chlorine exists as a mixture of isotopes with different masses.

Question 17

A student needs to prepare 0.20 moles of ammonia ($$NH_3) $$for a laboratory experiment. What mass of $$NH_3 is $$required? (Molar mass of $$NH_3 = 17.03 g/$$mol)

Accepted Answer

$$0.20 	imes 17.03 = 3.41$$ grams

Question 18

Which of the following is the correct sequence of steps to convert from grams of a substance to number of molecules?

Accepted Answer

Divide grams by molar mass to get moles, then multiply by Avogadro's number.

Question 19

A sample of calcium carbonate ($$CaCO_3) $$contains 0.50 moles. How many formula units are present?

Accepted Answer

$$0.50 	imes 6.022 	imes 10$$^{23}$$ = 3.011 	imes 10$$^{23}$$ formula units

Quantities in Chemical Reactions: Converting Grams to Moles and Atomic Mass Calculations

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