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$_2$O contains 18.02 molecules. What is the error in this statement?

1 mole of H$_2$O contains $6.022 \times 10^{23}$ molecules, not 18.02.

Q: If you have 0.500 mol of glucose (C$_6$H$_{12}$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$_2$O. How many molecules of H$_2$O 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$_9$H$_8$O$_4$). 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)

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$_2$O contains 18.02 molecules. What is the error in this statement?

Accepted Answer

1 mole of H$_2$O 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$_6$H$_{12}$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$_2$O. How many molecules of H$_2$O 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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