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

The number of particles equal to $$6.022 \times 10$$^{23}$$

Q: If $$21.5 cm$^3 of $$HCl is required to neutralize $$25 cm$^3 of $$sodium carbonate solution (prepared as above), what is the number of moles of HCl used? (HCl concentration is unknown)

$$n = C \times V = C \times 0.0215 (in $$litres)

Q: A student wants to prepare $$100 mL of$$ $$0.2 M $$NaCl solution. How many grams of NaCl are required? (Molar mass of NaCl = $$58.5 g/$$mol)

$$0.2 \times 0.1 \times 58.5 = 1.17 g$$

Q: Which calculation correctly converts grams to moles?

$$\text{moles} = \frac{\text{grams}}{\text{molar mass}}$$

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

$$\text{grams} = \text{moles} \times \text{molar mass}$$

Question 1

Which of the following best defines a mole in chemistry?

Accepted Answer

The number of particles equal to $$6.022 	imes 10$$^{23}$$

Question 2

If you have 1 gram of NaCl, how many moles of NaCl do you have? (Relative molar mass of NaCl = 58.5 g/mol)

Accepted Answer

$$0.017$$ moles

Question 3

A solution is prepared by dissolving $$3.65 g of $$HCl in $$1$$ litre of water. What is the molarity of the solution? (Molar mass of HCl = $$36.5 g/$$mol)

Accepted Answer

$$0.1$$ mol/L

Question 4

How many grams of sulfur are present in $$3.5$$ moles of sulfur? (Molar mass of sulfur = $$32 g/$$mol)

Accepted Answer

$$112 g$$

Question 5

You have $$500 g of $$iron. How many moles of iron do you have? (Molar mass of iron = $$56 g/$$mol)

Accepted Answer

$$8.93$$ moles

Question 6

In a titration, $$25 cm$^3 of $$NaOH is neutralized by $$20.3 cm$^3 of$$ $$0.1 M $$HCl. What is the molarity of the NaOH solution? (Reaction: $$\mathrm{NaOH} + \mathrm{HCl} \rightarrow \mathrm{NaCl} + \mathrm{H_2O})$$

Accepted Answer

$$0.0812 M$$

Question 7

Which of the following statements about molarity is correct?

Accepted Answer

Molarity is the number of moles of solute per litre of solution

Question 8

A chemist prepares a standard solution by dissolving $$1.35 g of $$sodium carbonate ($$\mathrm{Na_2CO_3}$$, molar mass $$= 106 g/$$mol) in $$250 cm$^3 of $$water. What is the concentration of this solution in mol/L?

Accepted Answer

$$0.051$$ mol/L

Question 9

If $$21.5 cm$^3 of $$HCl is required to neutralize $$25 cm$^3 of $$sodium carbonate solution (prepared as above), what is the number of moles of HCl used? (HCl concentration is unknown)

Accepted Answer

$$n = C 	imes V = C 	imes 0.0215 (in $$litres)

Question 10

Given the reaction $$\mathrm{Na_2CO_3} + 2\mathrm{HCl} \rightarrow 2\mathrm{NaCl} + \mathrm{CO_2$} + \mathrm{H_2O}$$, how many moles of HCl are required to react completely with $$0.01$$ moles of sodium carbonate?

Accepted Answer

$$0.02$$ moles

Question 11

Why do chemists prefer to use the mole as a unit when discussing the amount of substance?

Accepted Answer

Because it simplifies calculations involving extremely large numbers of particles

Question 12

A student wants to prepare $$100 mL of$$ $$0.2 M $$NaCl solution. How many grams of NaCl are required? (Molar mass of NaCl = $$58.5 g/$$mol)

Accepted Answer

$$0.2 	imes 0.1 	imes 58.5 = 1.17 g$$

Question 13

Which calculation correctly converts grams to moles?

Accepted Answer

$$	ext{moles} = \frac{	ext{grams}}{	ext{molar mass}}$$

Question 14

If $$0.1$$ moles of NaCl is dissolved in $$1$$ litre of water, what is the concentration of the solution?

Accepted Answer

$$0.1$$ mol/L

Question 15

A titration experiment uses $$25 cm$^3 of$$ $$0.051 M $$sodium carbonate solution to neutralize $$21.5 cm$^3 of $$HCl. What is the molarity of the HCl solution? (Reaction: $$\mathrm{Na_2CO_3} + 2\mathrm{HCl} \rightarrow 2\mathrm{NaCl} + \mathrm{CO_2$} + \mathrm{H_2O})$$

Accepted Answer

$$0.059 M$$

Question 16

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

Accepted Answer

$$	ext{grams} = 	ext{moles} 	imes 	ext{molar mass}$$

Question 17

Why is it important to scale down the preparation of solutions in the laboratory?

Accepted Answer

To reduce waste, cost, and safety risks while still working in moles per litre

Question 18

If $$1$$ mole of HCl is $$36.5 g$$, how many grams are in $$0.25$$ moles of HCl?

Accepted Answer

$$9.125 g$$

Question 19

A solution contains $$0.05$$ moles of solute in $$500 mL of $$solution. What is its molarity?

Accepted Answer

$$0.1$$ mol/L

Moles and Molarity: Foundations for Quantitative Chemistry

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