2B4 Solutions and Solubility Flashcards
Describe how solutions and their solubility depend on concentration, temperature, and the nature of solutes and solvents.
What is a solution?
A homogeneous mixture of two or more substances.
The components in a solution are uniformly distributed and cannot be easily separated by physical means.
What are the two main components of a solution?
- Solvent
- Solute
The solvent dissolves the solute. For example, in a saltwater solution, water is the solvent, and salt is the solute.
How does a solution differ from a heterogeneous mixture?
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.
What is the solute in a solution?
The substance that gets dissolved in the solvent.
In a sugar-water solution, sugar is the solute, and water is the solvent.
Fill in the blank:
The substance that dissolves the solute is called the ________.
solvent
Water is a common solvent because it dissolves many substances, such as sugar or salt.
Define:
Dilute solution
A solution that contains a relatively small amount of solute.
Example: A small spoonful of sugar in a large glass of water.
True or False:
A concentrated solution has a large amount of solute relative to solvent.
True
A thick syrup or concentrated juice is an example of a concentrated solution.
What does v/v stand for in concentration calculations?
volume/volume
A 10% (v/v) solution means 10 mL of solute in 100 mL of solution.
What does w/v stand for in concentration calculations?
weight/volume
A 5% (w/v) solution means 5 grams of solute in 100 mL of solution.
What happens when the temperature of a saturated solution is increased?
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.
Define:
Supersaturated solution
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.
What is a saturated solution?
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.
Fill in the blank:
A solution that can still dissolve more solute is called _________.
unsaturated
A glass of water can dissolve more salt until it reaches saturation.
True or False:
A supersaturated solution is stable and will not precipitate out solute.
False
Supersaturated solutions are unstable. Any disturbance, such as shaking or adding a seed crystal, will cause the solute to crystallize rapidly.
True or False:
A 10% (w/v) solution means 10 grams of solute in 100 mL of solution.
True
The unit (w/v) means weight per volume, so it is 10 grams of solute in 100 mL of solution.
What happens if a supersaturated solution is disturbed?
The solute crystallizes rapidly.
Supersaturated solutions are unstable and can shock into precipitation when disturbed.
True or False:
A solution that contains less solute than it can dissolve is called supersaturated.
False
A solution with less solute than it can dissolve is unsaturated. A supersaturated solution contains more solute than it can normally hold.
What does molarity (M) measure?
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.
How is molarity of a solution calculated?
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.
How is the percent concentration by mass calculated?
(Mass of solute / Mass of solution) × 100%
For example, A 10% salt solution means 10 grams of salt in every 100 grams of solution.
What is molality (m)?
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.
What is the unit of molality (m)?
mol/kg
For example, a 1 m solution contains 1 mole of solute dissolved in 1 kilogram of solvent.
How is molality different from molarity?
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.
Fill in the blank:
A 5% (w/v) solution means there are _____ grams of solute per 100 mL of solution.
5
w/v stands for weight/volume, so it means 5 grams of solute in 100 mL of solution.
What unit is used to measure the concentration of a solution in terms of moles per liter?
Molarity
Molarity (mol/L) is the unit used to express the concentration of a solution in terms of moles of solute per liter of solution.
True or False:
A 2 M solution of NaOH has 2 moles of NaOH dissolved in 2 liters of water.
False
A 2 M solution means 2 moles of NaOH are dissolved in 1 liter of solution, not 2 liters.
If 4 moles of NaCl are dissolved in 2 liters of solution, what is the molarity?
2 M
Molarity = 4 moles / 2 liters = 2 M.
What formula is used for diluting a solution?
M₁V₁ = M₂V₂
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.
If 200 mL of a 6 M NaCl solution is diluted to 500 mL, what is the new concentration?
2.4 M
Using the dilution formula: (6)(200) = (M₂)(500), so M₂ = 0.6 M.
How much water is needed to dilute 100 mL of 10 M NaOH to 1 M?
900 mL
Using M₁V₁ = M₂V₂: (10)(100) = (1)(V₂), so V₂ = 1000 mL. Thus, 900 mL of water is required.
What does the dilution formula M₁V₁ = M₂V₂ help calculate?
The final concentration or volume after dilution.
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.
True or False:
When a solution is diluted, the total amount of solute remains the same.
True
Dilution only adds solvent, reducing the concentration but not the solute amount.
If 50 mL of a 4 M solution is diluted to a 1 M solution, how much water must be added?
150 mL
Using the formula M₁V₁ = M₂V₂: (4)(50) = (1)(V₂), so V₂ = 200 mL. 150 mL of water is needed.
What is the molarity of a solution made by dissolving 4 grams of NaOH in 200 mL of water?
0.5 M
First, convert 4 grams of NaOH to moles using its molar mass, then divide by the volume in liters (0.2 L).
How many grams of NaCl are needed to make 250 mL of a 2 M solution?
29.2
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.
What is a polar solute?
A solute with positive and negative ends.
Water is an example of a polar solvent that dissolves polar solutes like salt, which dissociates into ions.
What is a nonpolar solute?
A solute without distinct positive or negative charges, which does not dissolve well in polar solvents.
Examples include oils, which dissolve in nonpolar solvents but not in polar ones like water.
True or False:
Oil dissolves easily in water.
False
Oil is nonpolar and does not mix with water, which is polar.
Fill in the blank:
A substance like hexane is a ________ solvent.
nonpolar
Hexane, a nonpolar solvent, dissolves nonpolar substances like oils but does not dissolve ionic or polar compounds like salt.
True or False:
Nonpolar solutes dissolve well in polar solvents.
False
Nonpolar solutes like grease do not dissolve in polar solvents such as water, as there are no attractive forces between them.
What are the factors that affect the rate of dissolving?
- Temperature
- Pressure
- Surface area
- Stirring
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.
Fill in the blank:
The rate of dissolving increases when the surface area of the solute is _________.
increased
A larger surface area allows more solute particles to interact with the solvent.
How does temperature affect the rate of dissolving?
Higher temperatures generally increase the rate of dissolving.
Heat provides more kinetic energy, causing solute particles to dissolve faster. This effect is especially noticeable for solid solutes in liquid solvents.
What happens in a solution when it reaches equilibrium between dissolving and crystallization?
Dissolving and crystallization rates are equal.
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.
True or False:
Increasing the pressure significantly speeds up the dissolving of solid solutes.
False
Pressure affects the solubility of gases in liquids but has minimal effect on solid solutes.
How does stirring affect the rate of dissolving?
By spreading solute particles.
It ensures fresh solvent molecules interact with the solute, speeding up the process.
True or False:
Crushing sugar into smaller grains increases its surface area, making it dissolve faster.
True
Smaller pieces expose more particles to the solvent for quicker dissolution.
What does solubility measure?
The maximum amount of solute that can dissolve in a solvent at a specific temperature and pressure.
Solubility depends on temperature, pressure, and the nature of the solute and solvent.
True or False:
The solubility of most solid solutes decreases with increasing temperature.
False
For most solids, solubility increases as temperature rises.
What is a solubility curve?
A graph showing solubility vs. temperature.
It visually represents how much solute can dissolve in a solvent at different temperatures.
What happens to the solubility of gases in water as temperature increases?
It decreases.
Higher temperatures give gas molecules more energy, causing them to escape from the solution.
True or False:
Solubility curves only apply to solid solutes in water.
False
Solubility curves can also be used for gases and other solvents, illustrating how solubility changes with temperature.
What type of solvent dissolves polar solutes?
Polar solvents
Water, a polar solvent, easily dissolves substances like salts and sugars because of its partial charges that interact with other polar molecules.
What type of solvent dissolves nonpolar solutes?
Nonpolar solvents
Nonpolar solvents, such as hexane, dissolve nonpolar solutes like oils due to similar intermolecular forces.
Fill in the blank:
Water is a ________ solvent.
polar
Water’s uneven charge distribution allows it to dissolve polar and ionic substances like salt and sugar.
What does the phrase “like dissolves like” mean?
Substances with similar polarities dissolve in each other.
For example, polar solvents like water dissolve polar solutes like salt, while nonpolar solvents like hexane dissolve nonpolar solutes like oils.
True or False:
Nonpolar molecules dissolve well in water.
False
Water, a polar solvent, doesn’t dissolve nonpolar substances like oil because they don’t interact with its dipoles.
What type of solvent would you use to dissolve iodine (I₂)?
A nonpolar solvent.
Iodine is a nonpolar molecule and dissolves best in nonpolar solvents like hexane.
Define:
Electrolyte
A substance that produces ions in solution, enabling electrical conductivity.
For example, NaCl dissociates into ions, allowing electrical conduction.
Why does NaCl in water conduct electricity?
NaCl dissociates into Na⁺ and Cl⁻ ions.
These free ions carry electrical charge through the solution, enabling conductivity.
True or False:
Sugar is an example of a nonelectrolyte.
True
Sugar dissolves in water but does not dissociate into ions, so it doesn’t conduct electricity.
What property of solutions is affected by electrolytes?
Electrical conductivity.
Electrolytes increase conductivity because they release ions into the solution that move freely and carry charge.
True or False:
The boiling point of a solution increases when nonvolatile solutes are added.
True
Adding solutes lowers the solvent’s vapor pressure, raising the boiling point and requiring more heat to boil.
How does adding a solute to a solvent affect the boiling point?
It raises the boiling point.
The solute particles reduce the solvent’s vapor pressure, which increases the temperature needed to reach boiling.
Fill in the blank:
An electrolyte solution ________ electrical current.
conducts
Electrolytes dissociate into ions, which move freely and allow the solution to conduct electricity.
What is freezing point depression?
The lowering of a solvent’s freezing point by adding a solute
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.
How does freezing-point depression relate to electrolytes?
Electrolytes lower the freezing point of solutions.
Electrolytes lower the freezing point by disrupting the formation of solid phases, requiring lower temperatures to freeze.
True or False:
Freezing point depression only applies to water.
False
Freezing point depression applies to all solvents, but the extent of depression depends on the amount of solute added.
What is boiling point elevation?
The rise in a solvent’s boiling point when a nonvolatile solute is added.
For example, adding salt to water increases its boiling point, meaning it will boil at a higher temperature.
True or False:
Boiling point elevation applies only to water.
False
Boiling point elevation applies to any solvent when a nonvolatile solute is added.
What is the relationship between solute concentration and boiling point elevation?
Higher solute concentration = greater boiling point elevation.
As solute particles increase, they lower the solvent’s vapor pressure, making it require more heat to reach the boiling point.
