2B4 Solutions and Solubility

Question 1

What is a solution?

Answer 1

A homogeneous mixture of two or more substances.

The components in a solution are uniformly distributed and cannot be easily separated by physical means.

Question 2

What are the two main components of a solution?

Answer 2

• Solvent
• Solute

The solvent dissolves the solute. For example, in a saltwater solution, water is the solvent, and salt is the solute.

Question 3

How does a solution differ from a heterogeneous mixture?

Answer 3

A solution is uniform; a heterogeneous mixture has distinct parts.

An example of a heterogeneous mixture is a salad, where you can see and separate the different ingredients.

Question 4

What is the solute in a solution?

Answer 4

The substance that gets dissolved in the solvent.

In a sugar-water solution, sugar is the solute, and water is the solvent.

Question 5

Fill in the blank:

The substance that dissolves the solute is called the ________.

Answer 5

solvent

Water is a common solvent because it dissolves many substances, such as sugar or salt.

Question 6

Define:

Dilute solution

Answer 6

A solution that contains a relatively small amount of solute.

Example: A small spoonful of sugar in a large glass of water.

Question 7

True or False:

A concentrated solution has a large amount of solute relative to solvent.

Answer 7

True

A thick syrup or concentrated juice is an example of a concentrated solution.

Question 8

What does v/v stand for in concentration calculations?

Answer 8

volume/volume

A 10% (v/v) solution means 10 mL of solute in 100 mL of solution.

Question 9

What does w/v stand for in concentration calculations?

Answer 9

weight/volume

A 5% (w/v) solution means 5 grams of solute in 100 mL of solution.

Question 10

What happens when the temperature of a saturated solution is increased?

Answer 10

The solution can dissolve more solute and may become supersaturated upon cooling.

Heating allows the solution to hold more solute. If cooled and excess solute stays dissolved, it becomes an unstable supersaturated solution.

Question 11

Define:

Supersaturated solution

Answer 11

A solution that temporarily holds more solute than it normally can at a given temperature.

If a supersaturated solution cools or is disturbed, the excess solute may crystallize out.

Question 12

What is a saturated solution?

Answer 12

A solution where no more solute can dissolve at a given temperature.

If you add sugar to tea and it starts to settle at the bottom, the solution is saturated.

Question 13

Fill in the blank:

A solution that can still dissolve more solute is called _________.

Answer 13

unsaturated

A glass of water can dissolve more salt until it reaches saturation.

Question 14

True or False:

A supersaturated solution is stable and will not precipitate out solute.

Answer 14

False

Supersaturated solutions are unstable. Any disturbance, such as shaking or adding a seed crystal, will cause the solute to crystallize rapidly.

Question 15

True or False:

A 10% (w/v) solution means 10 grams of solute in 100 mL of solution.

Answer 15

True

The unit (w/v) means weight per volume, so it is 10 grams of solute in 100 mL of solution.

Question 16

What happens if a supersaturated solution is disturbed?

Answer 16

The solute crystallizes rapidly.

Supersaturated solutions are unstable and can shock into precipitation when disturbed.

Question 17

True or False:

A solution that contains less solute than it can dissolve is called supersaturated.

Answer 17

False

A solution with less solute than it can dissolve is unsaturated. A supersaturated solution contains more solute than it can normally hold.

Question 18

What does molarity (M) measure?

Answer 18

The moles of solute per liter of solution.

Molarity is a concentration unit. For example, a 1 M solution contains 1 mole of solute dissolved in 1 liter of solution.

Question 19

How is molarity of a solution calculated?

Answer 19

Molarity = moles of solute / liters of solution.

For example, if 1 mole of NaCl is dissolved in 1 liter of water, the molarity is 1 M.

Question 20

How is the percent concentration by mass calculated?

Answer 20

(Mass of solute / Mass of solution) × 100%

For example, A 10% salt solution means 10 grams of salt in every 100 grams of solution.

Question 21

What is molality (m)?

Answer 21

The number of moles of solute per kilogram of solvent.

Molality is particularly important when temperature changes are involved since it doesn’t depend on volume, unlike molarity.

Question 22

What is the unit of molality (m)?

Answer 22

mol/kg

For example, a 1 m solution contains 1 mole of solute dissolved in 1 kilogram of solvent.

Question 23

How is molality different from molarity?

Answer 23

Molality is moles per kg of solvent, molarity is moles per L of solution.

Molality is based on the mass of the solvent (kg) and is unaffected by temperature, while molarity depends on the volume of the entire solution (L) and can change with temperature.

Question 24

Fill in the blank:

A 5% (w/v) solution means there are _____ grams of solute per 100 mL of solution.

Answer 24

5

w/v stands for weight/volume, so it means 5 grams of solute in 100 mL of solution.

Question 25

What **unit** is used to measure the concentration of a solution in terms of moles per liter?

Answer 25

Molarity ## Footnote Molarity (mol/L) is the unit used to express the **concentration** of a solution in terms of moles of solute per liter of solution.

Question 26

# True or False: A 2 M solution of **NaOH** has 2 moles of NaOH dissolved in 2 liters of water.

Answer 26

False ## Footnote A 2 M solution means 2 moles of NaOH are dissolved in **1 liter** of solution, not 2 liters.

Question 27

If 4 moles of NaCl are dissolved in 2 liters of solution, what is the **molarity**?

Answer 27

2 M ## Footnote Molarity = 4 moles / 2 liters = 2 M.

Question 28

What **formula** is used for diluting a solution?

Answer 28

M₁V₁ = M₂V₂ ## Footnote Where: M₁ = the initial concentration of the stock solution. V₁ = the volume of the stock solution required. M₂ = the final desired concentration. V₂ = the final volume of the diluted solution. This dilution formula helps calculate the final concentration or volume of a solution after dilution.

Question 29

If 200 mL of a 6 M NaCl solution is diluted to 500 mL, what is the **new** concentration?

Answer 29

2.4 M ## Footnote Using the dilution formula: (6)(200) = (M₂)(500), so M₂ = 0.6 M.

Question 30

How much **water** is needed to dilute 100 mL of 10 M NaOH to 1 M?

Answer 30

900 mL ## Footnote Using M₁V₁ = M₂V₂: (10)(100) = (1)(V₂), so V₂ = 1000 mL. Thus, 900 mL of water is required.

Question 31

What does the dilution formula M₁V₁ = M₂V₂ help **calculate**?

Answer 31

The final concentration or volume after dilution. ## Footnote This equation ensures that the total amount of solute stays constant before and after dilution, meaning no solute is added or removed during the process.

Question 32

# True or False: When a solution is diluted, the total amount of solute remains the **same**.

Answer 32

True ## Footnote **Dilution** only adds solvent, reducing the concentration but not the solute amount.

Question 33

If 50 mL of a 4 M solution is diluted to a 1 M solution, how much **water** must be added?

Answer 33

150 mL ## Footnote Using the formula M₁V₁ = M₂V₂: (4)(50) = (1)(V₂), so V₂ = 200 mL. 150 mL of water is needed.

Question 34

What is the **molarity** of a solution made by dissolving 4 grams of NaOH in 200 mL of water?

Answer 34

0.5 M ## Footnote First, convert 4 grams of NaOH to moles using its molar mass, then divide by the volume in liters (0.2 L).

Question 35

How many **grams** of NaCl are needed to make 250 mL of a 2 M solution?

Answer 35

29.2 ## Footnote Molarity = moles / volume; 2 moles/L × 0.25 L = 0.5 moles. Since NaCl has a molar mass of 58.44 g/mol, 0.5 moles = 29.2 grams.

Question 36

What is a **polar** solute?

Answer 36

A **solute** with positive and negative ends. ## Footnote **Water** is an example of a polar solvent that dissolves polar solutes like salt, which dissociates into ions.

Question 37

What is a **nonpolar** solute?

Answer 37

A solute **without** distinct positive or negative charges, which does not dissolve well in polar solvents. ## Footnote Examples include oils, which dissolve in nonpolar solvents but not in polar ones like water.

Question 38

# True or False: Oil **dissolves** easily in water.

Answer 38

False ## Footnote Oil is *nonpolar* and does not mix with water, which is polar.

Question 39

# Fill in the blank: A substance like **hexane** is a \_\_\_\_\_\_\_\_ solvent.

Answer 39

nonpolar ## Footnote Hexane, a nonpolar solvent, *dissolves* nonpolar substances like oils but does not dissolve ionic or polar compounds like salt.

Question 40

# True or False: Nonpolar solutes **dissolve** well in polar solvents.

Answer 40

False ## Footnote Nonpolar solutes like grease do not dissolve in polar solvents such as water, as there are no attractive forces between them.

Question 41

What are the **factors** that affect the rate of dissolving?

Answer 41

* Temperature * Pressure * Surface area * Stirring ## Footnote Increasing temperature or surface area and stirring can speed up the rate of dissolving. Higher pressure increases gas solubility but has little effect on solids and liquids.

Question 42

# Fill in the blank: The rate of dissolving **increases** when the surface area of the solute is \_\_\_\_\_\_\_\_\_.

Answer 42

increased ## Footnote A larger surface area **allows** more solute particles to interact with the solvent.

Question 43

How does **temperature** affect the rate of dissolving?

Answer 43

Higher temperatures generally **increase** the rate of dissolving. ## Footnote Heat provides more kinetic energy, causing solute particles to dissolve faster. This effect is especially noticeable for solid solutes in liquid solvents.

Question 44

What **happens** in a solution when it reaches **equilibrium** between dissolving and crystallization?

Answer 44

Dissolving and crystallization rates are equal. ## Footnote At this point, the solution is saturated, meaning it can no longer dissolve any more solute at the current temperature and pressure. The amount of solute in the solution remains constant as the rates of dissolving and crystallization balance each other out.

Question 45

# True or False: Increasing the pressure significantly **speeds** up the dissolving of solid solutes.

Answer 45

False ## Footnote Pressure affects the **solubility** of gases in liquids but has *minimal* effect on solid solutes.

Question 46

How does **stirring** affect the rate of dissolving?

Answer 46

By **spreading** solute particles. ## Footnote It ensures fresh solvent molecules interact with the solute, speeding up the process.

Question 47

# True or False: Crushing sugar into smaller grains increases its **surface area**, making it dissolve faster.

Answer 47

True ## Footnote Smaller pieces **expose** more particles to the solvent for quicker dissolution.

Question 48

What does **solubility** measure?

Answer 48

The **maximum** amount of solute that can dissolve in a solvent at a specific temperature and pressure. ## Footnote Solubility depends on temperature, pressure, and the nature of the solute and solvent.

Question 49

# True or False: The solubility of most solid solutes **decreases** with increasing temperature.

Answer 49

False ## Footnote For most solids, solubility increases as temperature rises.

Question 50

What is a **solubility curve**?

Answer 50

A **graph** showing solubility vs. temperature. ## Footnote It visually represents how much solute can dissolve in a solvent at different temperatures.

Question 51

What **happens** to the solubility of gases in water as **temperature** increases?

Answer 51

It decreases. ## Footnote Higher temperatures give gas molecules more energy, causing them to escape from the solution.

Question 52

# True or False: Solubility curves only apply to **solid solutes** in water.

Answer 52

False ## Footnote Solubility curves can also be used for gases and other solvents, illustrating how solubility changes with temperature.

Question 53

What **type** of solvent dissolves polar solutes?

Answer 53

Polar solvents ## Footnote Water, a polar solvent, easily dissolves substances like salts and sugars because of its partial charges that interact with other polar molecules.

Question 54

What **type** of solvent dissolves nonpolar solutes?

Answer 54

Nonpolar solvents ## Footnote Nonpolar solvents, such as hexane, dissolve nonpolar solutes like oils due to similar intermolecular forces.

Question 55

# Fill in the blank: **Water** is a \_\_\_\_\_\_\_\_ solvent.

Answer 55

polar ## Footnote Water’s uneven charge distribution allows it to dissolve polar and ionic substances like salt and sugar.

Question 56

What does the phrase "**like dissolves like**" mean?

Answer 56

Substances with **similar** polarities dissolve in each other. ## Footnote For example, polar solvents like water dissolve polar solutes like salt, while nonpolar solvents like hexane dissolve nonpolar solutes like oils.

Question 57

# True or False: Nonpolar molecules **dissolve** well in water.

Answer 57

False ## Footnote Water, a polar solvent, doesn’t dissolve nonpolar substances like oil because they don’t interact with its dipoles.

Question 58

What type of solvent would you use to dissolve **iodine** (I₂)?

Answer 58

A **nonpolar** solvent. ## Footnote Iodine is a nonpolar molecule and dissolves best in nonpolar solvents like hexane.

Question 59

# Define: Electrolyte

Answer 59

A substance that **produces** ions in solution, enabling electrical conductivity. ## Footnote For example, NaCl dissociates into ions, allowing electrical conduction.

Question 60

Why does **NaCl** in water conduct electricity?

Answer 60

NaCl **dissociates** into Na⁺ and Cl⁻ ions. ## Footnote These free ions carry electrical charge through the solution, enabling **conductivity**.

Question 61

# True or False: Sugar is an example of a **nonelectrolyte**.

Answer 61

True ## Footnote Sugar dissolves in water but does not dissociate into ions, so it doesn’t conduct electricity.

Question 62

What property of solutions is **affected** by electrolytes?

Answer 62

Electrical conductivity. ## Footnote **Electrolytes** increase conductivity because they release ions into the solution that move freely and carry charge.

Question 63

# True or False: The boiling point of a solution **increases** when nonvolatile solutes are added.

Answer 63

True ## Footnote Adding solutes lowers the solvent’s vapor pressure, raising the boiling point and requiring more heat to boil.

Question 64

How does adding a **solute** to a solvent affect the boiling point?

Answer 64

It **raises** the boiling point. ## Footnote The solute particles reduce the solvent’s vapor pressure, which increases the temperature needed to reach boiling.

Question 65

# Fill in the blank: An **electrolyte** solution \_\_\_\_\_\_\_\_ electrical current.

Answer 65

conducts ## Footnote Electrolytes dissociate into ions, which move freely and allow the solution to conduct electricity.

Question 66

What is **freezing point depression**?

Answer 66

The **lowering** of a solvent’s freezing point by adding a solute ## Footnote Adding salt to water, for example, lowers the water's freezing point, which is why salt is spread on roads in winter to prevent ice formation.

Question 67

How does freezing-point depression **relate** to electrolytes?

Answer 67

Electrolytes **lower** the freezing point of solutions. ## Footnote Electrolytes lower the freezing point by *disrupting* the formation of solid phases, requiring lower temperatures to freeze.

Question 68

# True or False: Freezing point depression only **applies** to water.

Answer 68

False ## Footnote Freezing point depression applies to **all solvents**, but the extent of depression depends on the amount of solute added.

Question 69

What is **boiling point elevation**?

Answer 69

The **rise** in a solvent’s boiling point when a nonvolatile solute is added. ## Footnote For example, adding salt to water increases its boiling point, meaning it will boil at a higher temperature.

Question 70

# True or False: Boiling point elevation applies only to **water**.

Answer 70

False ## Footnote Boiling point elevation **applies** to any solvent when a nonvolatile solute is added.

Question 71

What is the **relationship** between solute concentration and boiling point elevation?

Answer 71

**Higher** solute concentration = **greater** boiling point elevation. ## Footnote As solute particles increase, they lower the solvent’s vapor pressure, making it require more heat to reach the boiling point.