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

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

Q: Which of the following is the correct molar mass calculation for $$H_2O$$?

$$2 \times 1.01\ \mathrm{g/mol} + 16.00\ \mathrm{g/mol} = 18.02\ \mathrm{g/mol}$$

Q: Which of the following conversions is correct for finding the number of molecules in a given mass of a compound?

$$\text{mass} \rightarrow \text{moles} \rightarrow \text{number of molecules}$$

Q: How many molecules are present in $$9.01\ \mathrm{g} of$$ $$H_2O$$? (Molar mass of $$H_2O is$$ $$18.02\ \mathrm{g/mol}$$, Avogadro's number $$= 6.022 \times 10$$^{23}$$)

$$3.011 \times 10$$^{23}$$ molecules

Q: A chemist has $$54.06\ \mathrm{g} of$$ $$H_2O. $$How many molecules does this represent? (Molar mass of $$H_2O is$$ $$18.02\ \mathrm{g/mol}$$, Avogadro's number $$= 6.022 \times 10$$^{23}$$)

$$1.81 \times 10$$^{24}$$ molecules

Q: If you have $$0.75$$ moles of $$H_2O$$, how many molecules do you have? (Avogadro's number $$= 6.022 \times 10$$^{23}$$)

$$4.52 \times 10$$^{23}$$ molecules

Question 1

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

Accepted Answer

The mass of 1 mole of molecules of a compound, expressed in grams per mole.

Question 2

Given the molar mass of water ($$H_2O) is$$ $$18.02\ \mathrm{g/mol}$$, what is the mass in grams of $$1.75$$ moles of water?

Accepted Answer

$$31.535\ \mathrm{g}$$

Question 3

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

Accepted Answer

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

Question 4

If you have $$36.04\ \mathrm{g} of $$water ($$H_2O$$), how many moles do you have? (Molar mass of $$H_2O is$$ $$18.02\ \mathrm{g/mol})$$

Accepted Answer

$$2.00$$ moles

Question 5

What is the mass of $$0.5$$ moles of $$H_2O$$? (Molar mass of $$H_2O is$$ $$18.02\ \mathrm{g/mol})$$

Accepted Answer

$$9.01\ \mathrm{g}$$

Question 6

Which of the following is the correct molar mass calculation for $$H_2O$$?

Accepted Answer

$$2 	imes 1.01\ \mathrm{g/mol} + 16.00\ \mathrm{g/mol} = 18.02\ \mathrm{g/mol}$$

Question 7

A student needs to prepare $$45.05\ \mathrm{g} of$$ $$H_2O. $$How many moles of water does this represent? (Molar mass of $$H_2O is$$ $$18.02\ \mathrm{g/mol})$$

Accepted Answer

$$2.50$$ moles

Question 8

Which of the following conversions is correct for finding the number of molecules in a given mass of a compound?

Accepted Answer

$$	ext{mass} ightarrow 	ext{moles} ightarrow 	ext{number of molecules}$$

Question 9

How many molecules are present in $$9.01\ \mathrm{g} of$$ $$H_2O$$? (Molar mass of $$H_2O is$$ $$18.02\ \mathrm{g/mol}$$, Avogadro's number $$= 6.022 	imes 10$$^{23}$$)

Accepted Answer

$$3.011 	imes 10$$^{23}$$ molecules

Question 10

A chemist has $$54.06\ \mathrm{g} of$$ $$H_2O. $$How many molecules does this represent? (Molar mass of $$H_2O is$$ $$18.02\ \mathrm{g/mol}$$, Avogadro's number $$= 6.022 	imes 10$$^{23}$$)

Accepted Answer

$$1.81 	imes 10$$^{24}$$ molecules

Question 11

Which of the following best describes a 'formula unit'?

Accepted Answer

The simplest ratio of ions represented in an ionic compound.

Question 12

If a student has $$0.25$$ moles of $$H_2O$$, what is the mass in grams?

Accepted Answer

$$4.505\ \mathrm{g}$$

Question 13

Which step is necessary to convert grams of a compound to number of molecules?

Accepted Answer

Divide by molar mass, then multiply by Avogadro's number.

Question 14

A sample contains $$3.5$$ moles of $$H_2O. $$What is its mass in grams?

Accepted Answer

$$63.07\ \mathrm{g}$$

Question 15

Which of the following is NOT a correct use of the mole concept?

Accepted Answer

Using moles to measure the volume of a liquid at STP.

Question 16

If you have $$0.75$$ moles of $$H_2O$$, how many molecules do you have? (Avogadro's number $$= 6.022 	imes 10$$^{23}$$)

Accepted Answer

$$4.52 	imes 10$$^{23}$$ molecules

Question 17

A student dissolves $$18.02\ \mathrm{g} of$$ $$H_2O in a $$beaker. How many moles of water are present?

Accepted Answer

$$1.00$$ mole

Question 18

Which of the following is the correct sequence for converting mass of a compound to number of molecules?

Accepted Answer

Mass $$\rightarrow$$ Moles $$\rightarrow$$ Number of molecules

Question 19

If you have $$2.5$$ moles of $$H_2O$$, how many grams do you have? (Molar mass of $$H_2O is$$ $$18.02\ \mathrm{g/mol})$$

Accepted Answer

$$45.05\ \mathrm{g}$$

Chemical Composition and Moles: Calculating Mass from Moles

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