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

One mole of any substance contains $6.022 \times 10^{23}$ particles.

Q: A fish tank contains $18.0$ grams of water. How many molecules of water are present? (Molar mass of $H_2O = 18.0$ g/mol)

$6.022 \times 10^{23}$ molecules

Q: If $2$ moles of oxygen gas ($O_2$) are present, how many oxygen molecules are there?

$1.2044 \times 10^{24}$ molecules

Question 1

Which of the following best describes the role of Avogadro's number in chemistry?

Accepted Answer

It is the number of atoms in one mole of a substance.

Question 2

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

Accepted Answer

$0.5$ moles

Question 3

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

Accepted Answer

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

Question 4

A chemist needs to prepare $0.25$ moles of sodium chloride ($NaCl$). What mass of $NaCl$ is required? (Molar mass of $NaCl = 58.44$ g/mol)

Accepted Answer

$14.61$ g

Question 5

Which of the following statements about the mole concept is correct?

Accepted Answer

One mole of any substance contains $6.022 	imes 10^{23}$ particles.

Question 6

A fish tank contains $18.0$ grams of water. How many molecules of water are present? (Molar mass of $H_2O = 18.0$ g/mol)

Accepted Answer

$6.022 	imes 10^{23}$ molecules

Question 7

Which of the following best explains why helium is used in balloons instead of hydrogen?

Accepted Answer

Helium is less reactive and does not form explosive mixtures with air.

Question 8

If $2$ moles of oxygen gas ($O_2$) are present, how many oxygen molecules are there?

Accepted Answer

$1.2044 	imes 10^{24}$ molecules

Question 9

A reaction requires $0.75$ moles of carbon dioxide ($CO_2$). What is the mass of $CO_2$ needed? (Molar mass of $CO_2 = 44.0$ g/mol)

Accepted Answer

$33.0$ g

Question 10

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.

Question 11

A student dissolves $5.0$ grams of glucose ($C_6H_{12}O_6$) in water. What is the number of moles of glucose present? (Molar mass of glucose $= 180$ g/mol)

Accepted Answer

$0.0278$ moles

Question 12

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

Accepted Answer

Molar mass is numerically equal to atomic mass but expressed in grams per mole.

Question 13

A medical case requires $0.1$ moles of potassium chloride ($KCl$) to be administered. What mass of $KCl$ should be given? (Molar mass of $KCl = 74.55$ g/mol)

Accepted Answer

$7.455$ g

Question 14

Which of the following is NOT a correct use of the mole concept in real-world chemistry?

Accepted Answer

Measuring the volume of a liquid directly in moles.

Question 15

A chemist has $12.0$ grams of helium gas. How many moles of helium does this represent? (Molar mass of $He = 4.00$ g/mol)

Accepted Answer

$3.00$ moles

Question 16

Which formula is used to calculate the number of particles in a given number of moles?

Accepted Answer

$N = n 	imes N_A$

Question 17

A historical event involved the use of $2.5$ moles of hydrogen gas ($H_2$) in a chemical reaction. How many grams of $H_2$ were used? (Molar mass of $H_2 = 2.02$ g/mol)

Accepted Answer

$5.05$ g

Question 18

Which of the following is the correct value for Avogadro's number?

Accepted Answer

$6.022 	imes 10^{23}$

Question 19

A solution contains $0.2$ moles of sodium ions ($Na^+$). How many sodium ions are present?

Accepted Answer

$1.2044 	imes 10^{23}$ ions

Atoms, Elements, and Chemical Quantities: Key Concepts in Introductory Chemistry

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