Q: A sample contains $1.0272 \times 10^{20}$ atoms. If the molar mass of the element is $58.44 \ \mathrm{g/mol}$, what is the mass of the sample in grams? (Avogadro's number $N_A = 6.022 \times 10^{23}$)

$9.98 \times 10^{-3} \ \mathrm{g}$

Q: Which of the following is the correct definition of a mole in chemistry?

The amount of substance containing $6.022 \times 10^{23}$ particles

Question 1

Which of the following best describes the concept of atomic number in chemistry?

Accepted Answer

The number of protons in the nucleus of an atom

Question 2

A sample contains $1.0272 	imes 10^{20}$ atoms. If the molar mass of the element is $58.44 \ \mathrm{g/mol}$, what is the mass of the sample in grams? (Avogadro's number $N_A = 6.022 	imes 10^{23}$)

Accepted Answer

$9.98 	imes 10^{-3} \ \mathrm{g}$

Question 3

Which of the following statements about isotopes is correct?

Accepted Answer

Isotopes have the same atomic number but different mass numbers

Question 4

If a chemical reaction produces $0.0$ grams of product, which of the following is the most likely explanation?

Accepted Answer

The reaction did not occur or the limiting reactant was absent

Question 5

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

Accepted Answer

$n = \dfrac{N}{N_A}$

Question 6

A student is given a sample of silver containing $2.55 	imes 10^{22}$ atoms. How many moles of silver are present?

Accepted Answer

$0.0423$ moles

Question 7

Which of the following best explains why elements in the same group of the periodic table have similar chemical properties?

Accepted Answer

They have the same number of valence electrons

Question 8

A reaction requires $0.50$ moles of sodium chloride ($NaCl$). How many formula units of $NaCl$ does this represent? ($N_A = 6.022 	imes 10^{23}$)

Accepted Answer

$3.01 	imes 10^{23}$

Question 9

Which of the following is the correct definition of a mole in chemistry?

Accepted Answer

The amount of substance containing $6.022 	imes 10^{23}$ particles

Question 10

A chemist has $0.10$ moles of an unknown element. If the element is known to have a molar mass of $40.0 \ \mathrm{g/mol}$, what is the mass of the sample?

Accepted Answer

$4.0 \ \mathrm{g}$

Question 11

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

Accepted Answer

Atomic mass and molar mass are numerically equal but have different units

Question 12

A sample contains $3.00 	imes 10^{24}$ molecules of water. How many moles of water are present?

Accepted Answer

$4.98$ moles

Question 13

Which of the following is NOT a correct statement about Avogadro's number?

Accepted Answer

It is the number of grams in one mole of a substance

Question 14

A student dissolves $5.85 \ \mathrm{g}$ of $NaCl$ in water. What is the number of moles of $NaCl$ dissolved? (Molar mass of $NaCl = 58.5 \ \mathrm{g/mol}$)

Accepted Answer

$0.100$ moles

Question 15

Which of the following best explains why the mass of one mole of carbon-12 is exactly $12 \ \mathrm{g}$?

Accepted Answer

Because the atomic mass unit is defined based on carbon-12

Question 16

A sample of an element contains $1.20 	imes 10^{24}$ atoms. What is the number of moles present?

Accepted Answer

$1.99$ moles

Question 17

Which of the following is the correct formula for calculating the mass ($m$) of a sample given the number of moles ($n$) and molar mass ($M$)?

Accepted Answer

$m = n 	imes M$

Question 18

A chemist wants to prepare $0.25$ moles of $KCl$. What mass of $KCl$ is required? (Molar mass of $KCl = 74.6 \ \mathrm{g/mol}$)

Accepted Answer

$18.7 \ \mathrm{g}$

Question 19

Which of the following best describes the term 'limiting reactant' in a chemical reaction?

Accepted Answer

The reactant that determines the amount of product formed

Question 20

A reaction requires $2.00$ moles of oxygen gas ($O_2$). How many molecules of $O_2$ are needed?

Accepted Answer

$1.20 	imes 10^{24}$

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

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