Q: Which of the following best describes Avogadro's number, and what is its value?

The number of atoms in one mole of a substance; $6.022 \times 10^{23}$

Q: Which of the following statements about the mole is correct?

A mole is $6.022 \times 10^{23}$ particles of a substance.

Q: Which of the following best describes the relationship between mass, moles, and molar mass?

$\text{Moles} = \dfrac{\text{Mass (g)}}{\text{Molar Mass (g/mol)}}$

Question 1

Which of the following best describes Avogadro's number, and what is its value?

Accepted Answer

The number of atoms in one mole of a substance; $6.022 	imes 10^{23}$

Question 2

A sample contains $4.5$ grams of helium gas ($He$). Given that the molar mass of helium is $4.0$ g/mol, how many atoms of helium are present in the sample?

Accepted Answer

$1.13 	imes 10^{24}$ atoms

Question 3

Which of the following statements about the mole is correct?

Accepted Answer

A mole is $6.022 	imes 10^{23}$ particles of a substance.

Question 4

If you have $22.4$ liters of oxygen gas ($O_2$) at standard temperature and pressure (STP), how many moles of $O_2$ do you have?

Accepted Answer

$1$ mole

Question 5

A student dissolves $53$ grams of sodium chloride ($NaCl$) in water. The molar mass of $NaCl$ is $58.5$ g/mol. How many moles of $NaCl$ are present?

Accepted Answer

$0.91$ moles

Question 6

Which of the following best explains why the atomic mass of chlorine is approximately $35.5$ u (atomic mass units)?

Accepted Answer

It is the average of the masses of all isotopes of chlorine, weighted by their natural abundance.

Question 7

A chemical reaction requires $2.0$ liters of a $1.0$ M solution of hydrochloric acid ($HCl$). How many grams of $HCl$ are needed to prepare this solution? (Molar mass of $HCl = 36.5$ g/mol)

Accepted Answer

$73$ grams

Question 8

Which of the following is the correct balanced chemical equation for the combustion of methane ($CH_4$) in oxygen?

Accepted Answer

$CH_4 + 2O_2 \rightarrow CO_2 + 2H_2O$

Question 9

A patient receives an intravenous solution containing $0.9\%$ sodium chloride ($NaCl$) by mass. If the patient receives $500$ mL of this solution, how many grams of $NaCl$ does the patient receive?

Accepted Answer

$4.5$ grams

Question 10

Which of the following best describes the relationship between mass, moles, and molar mass?

Accepted Answer

$	ext{Moles} = \dfrac{	ext{Mass (g)}}{	ext{Molar Mass (g/mol)}}$

Question 11

A balloon contains $2.0$ moles of nitrogen gas ($N_2$) at STP. What is the volume of the gas in liters?

Accepted Answer

$44.8$ L

Question 12

Which of the following is a correct statement about isotopes?

Accepted Answer

Isotopes of an element have the same number of protons but different numbers of neutrons.

Question 13

A chemist needs to prepare $250$ mL of a $0.5$ M solution of potassium chloride ($KCl$). What mass of $KCl$ (molar mass $= 74.5$ g/mol) is required?

Question 14

Which of the following best explains why $CO_2$ is considered a compound and not a mixture?

Accepted Answer

Because $CO_2$ consists of two or more elements chemically bonded in a fixed ratio.

Question 15

A $2.0$ L solution contains $0.5$ moles of glucose ($C_6H_{12}O_6$). What is the molarity of the solution?

Accepted Answer

$0.25$ M

Question 16

Which of the following is the correct electron configuration for a neutral neon atom ($Ne$, atomic number $= 10$)?

Accepted Answer

$1s^2 2s^2 2p^6$

Question 17

A reaction produces $4.9 	imes 10^{22}$ molecules of water ($H_2O$). How many moles of water is this?

Accepted Answer

$0.081$ moles

Question 18

Which of the following best describes a chemical change?

Accepted Answer

A process in which new substances with different properties are formed.

Question 19

A $45$ g sample of a compound contains $15$ g of carbon, $5$ g of hydrogen, and $25$ g of oxygen. What is the percent by mass of oxygen in the compound?

Accepted Answer

$55.6\%$

Question 20

Which of the following is a physical property of matter?

Accepted Answer

Melting point

Atoms, Elements, and Chemical Quantities: Key Concepts and Calculations

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