Q: Which of the following best describes a mole in chemistry?

A mole is the amount of substance that contains $$6.022 \times 10$$^{23}$$ atoms, molecules, or ions.

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 of a substance.

Question 1

Which of the following best describes a mole in chemistry?

Accepted Answer

A mole is the amount of substance that contains $$6.022 	imes 10$$^{23}$$ atoms, molecules, or ions.

Question 2

If you have 12 grams of carbon ($$C$$), how many moles of carbon do you have? (Atomic mass of $$C = 12 g/$$mol)

Accepted Answer

$$1$$ mole

Question 3

Which equation correctly relates the number of moles ($$n$$), mass ($$m$$), and molar mass ($$M) of a $$substance?

Accepted Answer

$$n = \frac{m}{M}$$

Question 4

A compound contains $$2$$ moles of hydrogen atoms and $$1$$ mole of oxygen atoms. What is the empirical formula of this compound?

Accepted Answer

$$H_2O$$

Question 5

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 of a substance.

Question 6

A sample contains $$3.01 	imes 10$$^{23}$$ molecules of CO_2$. How many moles of CO_2$ are present?

Accepted Answer

$$0.5$$ moles

Question 7

Which of the following is the correct molar mass of water ($$H_2O$$)? (Atomic masses: $$H = 1 g/$$mol, $$O = 16 g/$$mol)

Accepted Answer

$$18 g/$$mol

Question 8

A chemist needs $$0.25$$ moles of sodium chloride ($$NaCl) $$for an experiment. What mass of $$NaCl$$ should be weighed out? (Molar mass of $$NaCl = 58.5 g/$$mol)

Accepted Answer

$$14.625 g$$

Question 9

Which of the following best explains why the mole is a useful unit in chemistry?

Accepted Answer

It allows chemists to count atoms, molecules, or ions by weighing macroscopic amounts of material.

Question 10

A reaction requires $$2$$ moles of $$H_2$$ and $$1$$ mole of $$O_2 to $$produce water. If you start with $$4$$ moles of $$H_2$$ and $$2$$ moles of $$O_2$$, how many moles of water can be produced?

Accepted Answer

$$4$$ moles

Question 11

Which formula is used to calculate the number of particles ($$N) in a $$given number of moles ($$n$$)?

Accepted Answer

$$N = n 	imes N_A$$

Question 12

A student has $$36$$ grams of water ($$H_2O). $$How many moles of water does the student have? (Molar mass of $$H_2O = 18 g/$$mol)

Accepted Answer

$$2$$ moles

Question 13

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

Accepted Answer

To measure the temperature of a substance.

Question 14

If $$1$$ mole of $$O_2$$ gas occupies $$22.4 L at $$STP, how many liters will $$3$$ moles of $$O_2$$ occupy at STP?

Accepted Answer

$$67.2 L$$

Question 15

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

Accepted Answer

$$2$$ moles

Question 16

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

Accepted Answer

The mass of one mole of a substance, expressed in grams per mole ($$g/mol).$$

Question 17

A medical laboratory needs $$0.1$$ moles of glucose ($$C_6H_{12}O_6$) for a test. What mass of glucose should be used? (Molar mass of C_6H$$_{12}$$O_6 = 180$ g/mol)

Accepted Answer

$$18 g$$

Question 18

Which of the following best describes the relationship between the number of moles and the number of particles in a sample?

Accepted Answer

The number of particles is equal to the number of moles multiplied by Avogadro's number.

Question 19

A historical event involved the synthesis of ammonia ($$NH_3) $$from nitrogen and hydrogen gases. If $$1$$ mole of $$N_2$$ reacts with $$3$$ moles of $$H_2$$, how many moles of $$NH_3$$ are produced?

Accepted Answer

$$2$$ moles

Question 20

Which of the following is the correct formula for calculating the mass ($$m) of a $$substance if you know the number of moles ($$n) $$and the molar mass ($$M$$)?

Accepted Answer

$$m = n 	imes M$$

Chemical Composition and Quantities in Chemical Reactions: Study Notes

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