Q: A sample contains 10.8 g of solid CO$$_2. $$How many CO$$_2$$ molecules are present? (Molar mass of CO$$_2 = 44.01 g/$$mol, Avogadro's number = $$6.022 \times 10$$^{23}$$ molecules/mol)

$$1.48 \times 10$$^{23}$$ molecules

Q: Which of the following is the correct conceptual plan for converting grams of a compound to number of molecules?

$$\text{grams} \rightarrow \text{moles} \rightarrow \text{molecules}$$

Q: A student claims that 1 mole of H$$_2O $$contains 18.02 molecules. What is the error in this statement?

1 mole of H$$_2O $$contains $$6.022 \times 10$$^{23}$$ molecules, not 18.02.

Q: If you have 0.500 mol of glucose (C$$_6H$_{12}O$_6$$), how many molecules of glucose do you have?

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

Q: Which of the following is the correct formula for calculating the number of moles from a given mass?

$$\text{moles} = \frac{\text{mass (g)}}{\text{molar mass (g/mol)}}$$

Q: A chemist has 5.00 g of H$$_2O. $$How many molecules of H$$_2O $$are present? (Molar mass = 18.02 g/mol, Avogadro's number = $$6.022 \times 10$$^{23}$$ molecules/mol)

$$1.67 \times 10$$^{23}$$ molecules

Q: A patient is prescribed 500 mg of a medication. The molar mass of the medication is 250 g/mol. How many molecules of the medication does the patient receive? (Avogadro's number = $$6.022 \times 10$$^{23}$$ molecules/mol)

$$1.20 \times 10$$^{21}$$ molecules

Question 1

Which of the following best describes the process for determining the number of molecules in a given mass of a compound?

Accepted Answer

Convert grams to moles using molar mass, then convert moles to molecules using Avogadro's number.

Question 2

A sample contains 10.8 g of solid CO$$_2. $$How many CO$$_2$$ molecules are present? (Molar mass of CO$$_2 = 44.01 g/$$mol, Avogadro's number = $$6.022 	imes 10$$^{23}$$ molecules/mol)

Accepted Answer

$$1.48 	imes 10$$^{23}$$ molecules

Question 3

An aspirin tablet contains 325 mg of acetylsalicylic acid (C$$_9H$_8O$_4). $$What is the first step to determine the number of molecules in the tablet?

Accepted Answer

Convert 325 mg to grams.

Question 4

Which equation correctly relates the number of molecules ($$N$$), the number of moles ($$n$$), and Avogadro's number ($$N_A$$)?

Accepted Answer

$$N = n 	imes N_A$$

Question 5

If you have $$3.55 	imes 10$$^{22}$$ molecules of H_2$O, what is the mass of this sample? (Molar mass of H_2$O = 18.02 g/mol, Avogadro's number = 6.022$$ 	imes $$10^{23}$$ molecules/mol)

Accepted Answer

1.06 g

Question 6

A chemist needs to prepare a sample containing exactly $$1.00 	imes 10$$^{24}$$ molecules of CO_2$. What mass of CO_2$ should be weighed out? (Molar mass of CO_2$ = 44.01 g/mol, Avogadro's number = 6.022$$ 	imes $$10^{23}$$ molecules/mol)

Accepted Answer

Question 7

Which of the following is the correct conceptual plan for converting grams of a compound to number of molecules?

Accepted Answer

$$	ext{grams} ightarrow 	ext{moles} ightarrow 	ext{molecules}$$

Question 8

A student claims that 1 mole of H$$_2O $$contains 18.02 molecules. What is the error in this statement?

Accepted Answer

1 mole of H$$_2O $$contains $$6.022 	imes 10$$^{23}$$ molecules, not 18.02.

Question 9

Which real-world scenario best illustrates the use of molar mass and Avogadro's number in a medical context?

Accepted Answer

Calculating the number of acetylsalicylic acid molecules in an aspirin tablet to ensure proper dosage.

Question 10

If you have 0.500 mol of glucose (C$$_6H$_{12}O$_6$$), how many molecules of glucose do you have?

Accepted Answer

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

Question 11

A sample of dry ice (CO$$_2) $$weighs 22.0 g. How many moles of CO$$_2$$ are present? (Molar mass of CO$$_2 = 44.01 g/$$mol)

Accepted Answer

0.500 mol

Question 12

Which of the following is the correct formula for calculating the number of moles from a given mass?

Accepted Answer

$$	ext{moles} = \frac{	ext{mass (g)}}{	ext{molar mass (g/mol)}}$$

Question 13

A chemist has 5.00 g of H$$_2O. $$How many molecules of H$$_2O $$are present? (Molar mass = 18.02 g/mol, Avogadro's number = $$6.022 	imes 10$$^{23}$$ molecules/mol)

Accepted Answer

$$1.67 	imes 10$$^{23}$$ molecules

Question 14

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

Accepted Answer

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

Question 15

A patient is prescribed 500 mg of a medication. The molar mass of the medication is 250 g/mol. How many molecules of the medication does the patient receive? (Avogadro's number = $$6.022 	imes 10$$^{23}$$ molecules/mol)

Accepted Answer

$$1.20 	imes 10$$^{21}$$ molecules

Question 16

Which step is NOT necessary when converting from molecules to grams?

Accepted Answer

Convert grams to liters using molar volume.

Molar Mass as a Conversion Factor

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