🧪AP Chemistry
6 min read•Last Updated on June 18, 2024
Dalia Savy
Kanya Shah
Dalia Savy
Kanya Shah
We're back to solutions! Remember that solutions are homogeneous mixtures where the particles are evenly mixed and the solute is uniformly distributed within the solvent. The solute is the substance that is dissolved, while the solvent is the substance that does the dissolving.
We discussed how to calculate the concentration of a solute dissolved in a solvent, but what does this value depend on? Let's go over solubility!
To put it simply, solubility is the ability of a substance to dissolve in a solvent to form a homogeneous mixture. A substance that is soluble in a solvent will dissolve completely to form a solution, while a substance that is insoluble in a solvent will not dissolve and will remain in a separate phase.
The solubility of one substance in another depends on:
👉 Make sure to review intermolecular forces as they will constantly come back in this course!
There are a few solubility rules that will be helpful on the AP Exam and we will return back to these when we discuss precipitation reactions in unit four:
You can easily notice that many of the same ions (notably Ag, Hg2 2+, and Pb2+) are often exceptions to these solubility rules. However, do not try to memorize these completely! These, like things like polyatomic ions, are memorized implicitly through usage! That's why by the end of AP Chemistry, most students don't think about charts like these, they simply know them through doing a bajillion problems.
Every solution, no matter the solute and solvent, has something called a saturation point. Essentially, this is the point at which no more solute can be dissolved in the solvent.
It depends on three things: the temperature, the solvent, and the solute. At a higher temperature, more solute can be dissolved (for the majority of solutes). This can be seen in the following solubility curve:
Solubility curves are graphs that show the relationship between the solubility of a substance in a solvent and the temperature of that solvent. These curves are especially helpful when predicting the solubility of a substance at different temperatures.
When learning about a new type of graph, you always want to note the axes:
Take a look at the dark blue curve that represents the solubility of potassium chloride (KCl). At approximately 70 degrees Celcius, there will be almost 50 grams of KCl dissolved in the solution. This value specifically forms a saturated solution.
** Practice reading these graphs and ensuring you understand what information can be obtained from them, as well as what relationship is shown.**
A saturated solution is a solution in which the maximum amount of solute has been dissolved in a solvent at a specific temperature. You can also think about solubility as the amount of solute needed to form a saturated solution at any particular temperature.
Once you have reached the saturation point, any additional solute (at that temperature) will fall out of the solution and not dissolve. Essentially, with saturated solutions, you are on the solubility curve. ⚖️
Undersaturated solutions are what their name implies - a solution that has not yet reached saturation. ⬇️
With an undersaturated solution, you can add more solute and it will continue to dissolve (with the temperature remaining constant). Like saturated solutions, an undersaturated solution can be modeled using a solubility curve, representing a point below the solubility curve.
Supersaturated solutions are a type of solution where you have more solute than you can dissolve in the solvent. You have basically surpassed the saturation point. ⬆️
In order to accomplish this, a chemist heats up the solution and then adds enough solute to saturate it at that temperature. The chemist would then slowly cool the solution down to the temperature they desire. This creates a supersaturated solution that when agitated will produce crystals. These crystals are extra solutes coming out of the solution, allowing the supersaturated solution to return to its saturated state.
With this being said, you can identify when a solution will be supersaturated by looking above the solubility curve on a graph.
The solubility of a substance is influenced by several factors, including the temperature of the solvent, the concentration of the solvent, and the presence of other substances.
As mentioned before, the polarity of both the solvent and solutes has a huge effect on solubility. This concept can always be thought of as "like dissolves like." Nonpolar substances are more likely to dissolve in nonpolar solvents and polar substances are more likely to dissolve in polar solvents.
Pressure only affects the solubility of gases. At higher pressures, more gas can be dissolved in the solvent, while at lower pressures, less gas will dissolve. In other words, as pressure increases, solubility increases as well. This phenomenon explains why soda🥤 becomes flat over time.
This can also be seen using Henry's Law: C = kP, where...
For solids and liquids, pressure does not affect solubility. This is very important and you will have to start paying attention to the phase at which the compounds you are discussing are in.
As mentioned before when taking a look at solubility curves, as temperature increases, the solubility of solids and liquids increases as well. This is due to the increased kinetic energy of the solvent molecules at higher temperatures, allowing them to more effectively dissolve the solute. Remember, temperature can be thought of as the average kinetic energy of particles.
This trend is different for gases: as temperature increases, the solubility of the gas decreases.
👉This will be discussed in greater depth when we go over unit seven later in this course.
The solubility of a substance generally increases as the concentration of the solvent increases. This is due to the increased number of solvent molecules present, which allows for more solute to dissolve.
The solubility of a substance can be influenced by the presence of other substances, such as electrolytes or solutes. The presence of these substances can affect the solubility of the solute by altering the chemical nature of the solvent or by competing for the same binding sites on the solvent molecules.
The solubility of a substance is generally influenced by the surface area of the solute. A smaller solute particle size will generally increase the solubility of the substance, as it allows for a greater surface area to be exposed to the solvent.
Concentration refers to how much solute is present compared to solvent. In other words, it's a measure of how much of one substance (the solute) is dissolved in another (the solvent).
Term 1 of 17
Concentration refers to how much solute is present compared to solvent. In other words, it's a measure of how much of one substance (the solute) is dissolved in another (the solvent).
Term 1 of 17
Concentration refers to how much solute is present compared to solvent. In other words, it's a measure of how much of one substance (the solute) is dissolved in another (the solvent).
Term 1 of 17
Solute is the substance that gets dissolved in a solution.
Solvent: The substance that does the dissolving in a solution.
Concentration: The measure of how much solute is present per unit volume or mass of solvent or solution.
Molarity: A way to express concentration; it's defined as moles of solute per liter of solution.
A solvent is a substance that dissolves a solute (a chemically different liquid, solid or gas), resulting in a solution.
Solute: This is what gets dissolved by the solvent - like our party guests.
Solution: The result when a solute is fully dissolved in a solvent - the successful party.
Concentration: How much solute is dissolved in the solvent - akin to how many guests are at our party.
Solubility is the maximum amount of a solute that can be dissolved in a solvent at a given temperature.
Solvent: A substance, usually liquid, capable of dissolving another substance (solute).
Saturated Solution: A solution in which no more solute can be dissolved at a specific temperature and pressure.
Supersaturated Solution: A state of a solution that contains more of the dissolved material than could be dissolved by the solvent under normal circumstances.
A homogeneous mixture is a type of mixture in which the components are uniformly distributed throughout, and cannot be visually distinguished from one another.
Solution: A type of homogeneous mixture formed when one substance (the solute) dissolves into another (the solvent).
Colloid: A type of homogeneous mixture where tiny particles are dispersed in another substance but do not settle out.
Suspension: Unlike a homogeneous mixture, this is a heterogeneous mixture where visible particles settle out over time.
These are the forces that occur between molecules. They're weaker than intramolecular forces but still crucial for determining properties like boiling and melting points.
London Dispersion Forces: These are weak intermolecular attractions resulting from instantaneous changes in electron density in a molecule.
Dipole-Dipole Interactions: These occur when polar molecules align such that positive and negative ends line up with each other.
Hydrogen Bonds: A special type of dipole-dipole interaction involving hydrogen atom bonded to highly electronegative elements like oxygen or nitrogen.
The saturation point refers to the stage at which no more solute can be dissolved into a solvent at a given temperature. Any additional solute will simply remain undissolved.
Solubility: The maximum amount of solute that can be dissolved in a solvent at a given temperature.
Supersaturation: A state where more solute is dissolved in a solvent than normally possible under stable conditions. It's like squeezing more passengers onto an already full bus!
Unsaturated Solution: A solution that contains less solute than the maximum amount it can dissolve at a given temperature. It's like a bus with empty seats, ready for more passengers!
A solubility curve is a graphical representation that illustrates the amount of a substance (solute) that can be dissolved in a solvent at various temperatures.
Solvent: This is the substance in which another substance (the solute) is dissolved. It's like the forest through which you're hiking.
Solute: This is the substance that gets dissolved in another substance. It's like your backpack - it goes wherever you go, but it becomes part of your overall experience.
Supersaturated Solution: This is when more solute has been dissolved in a solution than would normally be possible under stable conditions. It's like overpacking for your hike - sure, you might be able to carry everything for awhile, but eventually something's going to have to give!
Potassium chloride is an ionic compound often used as a source of potassium in fertilizers and medicine. Its chemical formula is KCl.
Ionic Compound: These are compounds formed by ions bonding together through electrostatic forces. They're like actors and actresses coming together to make a movie – they each bring their unique characteristics and combine them to create something new.
Cation: This is a positively charged ion. It's like the popcorn – it's what you're really there for.
Anion: This is a negatively charged ion. It's like the salt – it enhances the overall experience, but too much can be overwhelming.
A saturated solution is one in which no more solute can be dissolved at a given temperature and pressure.
Unsaturated Solution: This is when less than the maximum amount of solute has been dissolved in a solution. It's like an under-booked concert - there's still plenty of room for more attendees!
Solubility: This refers to the ability of a substance to dissolve in another substance. It’s like how popular or well-known the band playing at the concert is - if they're very popular, they'll attract more fans (dissolve more solute).
Precipitate: When a solution becomes supersaturated, any extra solute will form solid particles that fall out of solution, known as precipitate. It’s like if too many people show up for the concert and some are forced to leave, creating a crowd outside.
An undersaturated solution is a solution that contains less solute than the maximum amount it can dissolve at a given temperature.
Solute: The substance that gets dissolved in a solution.
Solvent: The substance that does the dissolving in a solution.
Saturation Point: The point at which no more solute can be dissolved in a solvent at a given temperature.
A supersaturated solution is one where more solute is dissolved than would normally be possible under normal conditions. It's unstable and can often lead to rapid precipitation of the solute when disturbed.
Precipitation Reaction: A chemical reaction where an insoluble solid (precipitate) forms and separates from the liquid mixture.
Solubility Equilibrium: The equilibrium between an undissolved solute and an ionic compound in a saturated solution.
Crystallization Process: The process by which crystals form from a supersaturated solution when it cools or evaporates.
Concentration refers to how much solute is present compared to solvent. In other words, it's a measure of how much of one substance (the solute) is dissolved in another (the solvent).
Molarity: A unit of concentration, defined as the number of moles of solute per liter of solution.
Solubility: The maximum amount of solute that can dissolve in a solvent at a given temperature.
Dilution: The process by which the concentration of a solution is reduced, usually by adding more solvent.
This refers to the effect that other substances in a reaction mixture can have on the rate of a chemical reaction. These substances may act as catalysts or inhibitors, speeding up or slowing down the reaction.
Catalyst: A substance that increases the rate of a chemical reaction without itself undergoing any permanent chemical change.
Inhibitor: A substance that slows down or prevents a particular chemical reaction.
Reaction Rate: The speed at which reactants are converted into products in a chemical reaction.
Polarity refers to the distribution of electric charges in a molecule, leading to regions of positive and negative charge. It determines how molecules interact with each other.
Nonpolar Molecules: These are molecules where electrons are shared equally by the atoms, resulting in no charge separation.
Dipole Moment: This is a measure of the overall polarity of a molecule.
Hydrogen Bonding: A type of intermolecular force that occurs when a hydrogen atom bonded to an electronegative atom interacts with another electronegative atom. It's stronger due to polarity.
Pressure is defined as force per unit area applied in a direction perpendicular to the surface of an object.
Atmospheric Pressure: This refers to the force exerted by air weight on all surfaces around us. It's like being at sea level where there are many 'layers' of air above us applying pressure.
Pascal (Pa): This is the standard unit of pressure in International System of Units (SI). It's equivalent to one newton per square meter.
Boyle’s Law: Boyle’s law states that for any gas at constant temperature, its volume inversely proportional to its pressure - just like how squeezing an inflated balloon decreases its volume while increasing its internal pressure.
Henry's Law states that at a constant temperature, the amount of a given gas that dissolves in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid.
Solubility: The maximum amount of solute that can dissolve in a solvent at a given temperature.
Partial Pressure: The individual pressure contribution each gas makes within a mixture.
Gas-Liquid Equilibrium: The state where no net change occurs in amounts of gaseous and dissolved phases under constant conditions such as temperature or pressure.
In chemistry, surface area refers to the total area that the surface of an object occupies. It's important in reactions as it can affect how quickly a reaction occurs.
Reaction Rate: How fast or slow a chemical reaction takes place. Like how long it takes for your popcorn to pop in microwave!
Catalyst: A substance that increases the rate of a chemical reaction without being consumed by the reaction itself. Like a cheerleader at a game who helps boost team spirit but doesn't play in game!
Reactant: A substance that undergoes change during a reaction. Think about baking cookies - flour, sugar, and butter are your reactants!