Concentration Units: Master Molarity, Molality, and Percent Composition

Question 1

Which unit of concentration expresses the number of moles of solute per kilogram of solvent?

Accepted Answer

Molality

Answer

Molarity

Answer

Percent composition

Question 2

Which of the following solutions has the lowest concentration of solute?

Accepted Answer

A 0.1 M solution

Answer

A 1 m solution

Answer

A 10% (w/v) solution

Question 3

Which of the following solutions has the highest freezing point?

Accepted Answer

Pure water

Answer

A 0.1 M NaCl solution

Answer

A 0.1 M glucose solution

Question 4

A solution is made by adding 50 g of KCl to 250 g of water. What is the percent composition of the solution on a mass basis?

Accepted Answer

16.7%

Answer

20%

Answer

25%

Question 5

Which of the following is a dimensionless unit for expressing concentration?

Accepted Answer

Percent by mass

Answer

Molarity

Answer

Molality

Question 6

A solution is prepared by dissolving 0.1 mole of NaCl in 1 liter of water. What is the molarity of the solution?

Accepted Answer

0.1 M

Answer

0.2 M

Answer

0.5 M

Answer

1.0 M

Question 7

What is the molality of a solution prepared by dissolving 1 mole of NaCl in 1 kg of water?

Accepted Answer

1 m

Answer

0.5 m

Answer

2 m

Answer

3 m

Question 8

Which of the following is the correct formula for calculating percent composition?

Accepted Answer

(Mass of solute / Mass of solution) x 100

Answer

(Mass of solute / Volume of solution) x 100

Answer

(Volume of solute / Mass of solution) x 100

Answer

(Volume of solute / Volume of solution) x 100

Question 9

What is the difference between molarity and molality?

Accepted Answer

Molarity is based on volume, while molality is based on mass.

Answer

Molality is based on volume, while molarity is based on mass.

Answer

Molarity and molality are the same thing.

Answer

Molarity is used for liquid solutions, while molality is used for gaseous solutions.

Question 10

What is the formula used to calculate molarity (M)?

Accepted Answer

Moles of solute per liters of solution

Answer

Moles of solute per kilograms of solution

Answer

Mass of solute per moles of solution

Answer

Volume of solution in liters per mass of solute

Question 11

A solution contains 0.25 moles of NaCl dissolved in 500 milliliters of water. What is the molarity of the solution?

Accepted Answer

0.25 M

Answer

0.125 M

Answer

0.5 M

Answer

1.0 M

Question 12

In chemistry, what is the definition of 'concentration' and why is it a crucial concept?

Accepted Answer

Concentration is the amount of solute dissolved in a given amount of solution.

Answer

Concentration is the speed at which a chemical reaction occurs.

Answer

Concentration is the physical state of a chemical substance.

Answer

Concentration is the color or shade of a solution.

Question 13

Which of the following is the IUPAC-recommended unit of concentration?

Accepted Answer

Molarity

Answer

Molality

Answer

Percentage Composition

Question 14

A solution is prepared by dissolving 1 mole of NaCl in 1 liter of water. What is the molarity of this solution?

Accepted Answer

1 M

Answer

0.1 M

Answer

10 M

Question 15

Which of the following is NOT a factor that affects the concentration of a solution?

Accepted Answer

Pressure

Answer

Temperature

Answer

Volume of the solution

Question 16

Which of the following expresses the concentration of a solution as a percentage of the total mass?

Accepted Answer

Percentage Composition

Answer

Molarity

Answer

Molality

Question 17

The SI unit of concentration is:

Accepted Answer

Moles per liter

Answer

Percent by mass

Answer

Grams per milliliter

Answer

Parts per million

Question 18

Which of the following factors does NOT affect the concentration of a solution?

Accepted Answer

Pressure

Answer

Amount of solute

Answer

Volume of solution

Answer

Temperature

Question 19

A 2 m molal solution means that:

Accepted Answer

There are 2 moles of solute per 1 kg of solvent

Answer

There are 2 moles of solute per 1 L of solution

Answer

There are 2 moles of solvent per 1 kg of solute

Answer

There are 2 kg of solvent per 1 mole of solute

Question 20

Which of the following solutions has the highest percent by mass of solute?

Accepted Answer

10 g of solute in 100 g of solution

Answer

10 g of solute in 200 g of solution

Answer

10 g of solute in 300 g of solution

Answer

10 g of solute in 400 g of solution

Question 21

The mole fraction of a solution that contains 3 moles of solute and 5 moles of solvent is:

Accepted Answer

0.4

Answer

0.2

Answer

0.6

Answer

0.8

Question 22

Which of the following concentration units is best suited for expressing the concentration of a gas?

Accepted Answer

Parts per million

Answer

Molarity

Answer

Molality

Answer

Percent by mass

Question 23

Which of the following is a colligative property?

Accepted Answer

Boiling point elevation

Answer

Density

Answer

Solubility

Answer

Viscosity

Question 24

What is the relationship between the concentration of a solution and its freezing point?

Accepted Answer

The freezing point decreases with increasing concentration

Answer

The freezing point increases with increasing concentration

Answer

The freezing point remains constant regardless of concentration

Answer

The relationship is not predictable

Question 25

Which of the following is the International System of Units (SI) unit of concentration?

Accepted Answer

Molarity (M)

Answer

Parts per million (ppm)

Answer

Mole percent (mol%)

Answer

Percent mass per volume (% m/v)

Question 26

A solution contains 2 moles of potassium chloride (KCl) in 1 kg of water. What is the molality of this solution?

Accepted Answer

1 m

Answer

0.5 m

Answer

2 m

Answer

3 m

Question 27

A solution is prepared by dissolving 10 grams of solute in 100 mL of solvent. What is the percent composition (m/v) of this solution?

Accepted Answer

10%

Answer

1%

Answer

15%

Answer

20%

Question 28

A 10% (m/v) solution is prepared by dissolving 10 grams of solute in 100 grams of solvent. What is the mass of the solvent used?

Accepted Answer

100 grams

Answer

50 grams

Answer

150 grams

Answer

200 grams

Question 29

What is the SI unit of molarity?

Accepted Answer

mol/L

Answer

mol/kg

Answer

g/L

Answer

ppm

Question 30

Which of the following solutions has the highest concentration?

Accepted Answer

1.0 M NH3

Answer

0.5 M NaCl

Answer

0.1 M NaOH

Answer

0.05 M HCl

Question 31

Define molality.

Accepted Answer

Moles of solute per kilogram of solvent

Answer

Moles of solute per liter of solution

Answer

Moles of solute per kilogram of solution

Answer

Grams of solute per liter of solution

Question 32

Which of the following solutions is the most concentrated in terms of percent composition?

Accepted Answer

40% HCl

Answer

10% NaCl

Answer

20% NaOH

Answer

30% NH3

Question 33

Which of the following is considered a dilute solution?

Accepted Answer

0.1 M NaCl

Answer

1.0 M NaOH

Answer

10% NH3

Answer

20% HCl

Question 34

What are the advantages of expressing concentration in units other than molarity, molality, and percent composition, such as parts per million (ppm) or parts per billion (ppb)?

Accepted Answer

ppm and ppb are particularly useful for expressing very dilute solutions.

Answer

ppm and ppb provide more precise measurements than molarity or molality.

Answer

ppm and ppb are simpler to calculate compared to molarity or molality.

Answer

ppm and ppb are rarely used in scientific research.

Question 35

Which concentration unit expresses the number of moles of solute per kilogram of solvent?

Accepted Answer

Molality (m)

Answer

Parts per million (ppm)

Answer

Molarity (M)

Answer

Percent composition (%)

Question 36

Which of the following is NOT a limitation of using percent composition as a concentration unit?

Accepted Answer

It can be used for both solids and liquids.

Answer

It can be affected by the presence of impurities.

Answer

It cannot be used for stoichiometric calculations.

Answer

It is temperature-dependent.

Question 37

Which of the following is a practical application of molarity?

Accepted Answer

Preparing solutions for chemical reactions.

Answer

Calculating the density of liquids.

Answer

Measuring the purity of water.

Question 38

What is the molarity of a solution prepared by dissolving 0.5 moles of NaCl in enough water to make 250 mL of solution?

Accepted Answer

2.0 M

Answer

0.5 M

Answer

0.25 M

Answer

1.0 M

Question 39

A solution contains 10 g of NaOH in 500 mL of solution. What is the mass percent of NaOH in the solution?

Accepted Answer

2.0%

Answer

5.0%

Answer

0.2%

Answer

10%

Question 40

How many grams of glucose (C6H12O6) are needed to prepare 1 L of a 0.5 M solution?

Accepted Answer

90 g

Answer

180 g

Answer

360 g

Answer

45 g

Question 41

What is the molality of a solution containing 0.2 moles of solute in 500 g of solvent?

Accepted Answer

0.4 m

Answer

0.1 m

Answer

0.2 m

Answer

1.0 m

Question 42

Which of the following units of concentration is NOT dependent on temperature?

Accepted Answer

Molality

Answer

Percent by volume

Answer

Percent by mass

Answer

Molarity

Question 43

A solution is prepared by dissolving 20 g of NaCl in 180 g of water. What is the mole fraction of NaCl in the solution?

Accepted Answer

0.036

Answer

0.100

Answer

0.111

Question 44

You have a 2.0 M solution of HCl and need to prepare 100 mL of a 0.5 M solution. How much of the stock solution should you use?

Accepted Answer

25 mL

Answer

200 mL

Answer

100 mL

Answer

50 mL

Question 45

What is the volume percent of ethanol in a solution prepared by mixing 25 mL of ethanol with enough water to make a total volume of 100 mL?

Accepted Answer

25%

Answer

50%

Answer

75%

Question 46

Which of the following concentration units is most appropriate for expressing the solubility of a gas in a liquid?

Accepted Answer

Molarity

Answer

Mole fraction

Answer

Mass percent

Answer

Molality

Question 47

A solution is prepared by dissolving 10 g of NaOH in water to make a final volume of 250 mL. What is the molarity of the solution? (Molar mass of NaOH = 40 g/mol)

Accepted Answer

1.0 M

Answer

0.1 M

Answer

0.25 M

Answer

4.0 M