Join our community

Learn Morecaret down

caret down

Join our community

Fiveable Community students are already meeting new friends, starting study groups, and sharing tons of opportunities for other high schoolers. Soon the Fiveable Community will be on a totally new platform where you can share, save, and organize your learning links and lead study groups among other students! 🎉

group of students
group of students

ap chem study guides

🌀  Unit 3 - Intermolecular Forces and Properties

👟  Unit 5 - Kinetics

🔥  Unit 6 - Thermodynamics

⚖️  Unit 7 - Equilibrium

  Unit 9 - Applications of Thermodynamics

🤺  AP Chemistry Essentials

3.10 Solubility and Solubility Rules

#solubility

#saturation

#solubilityrules

⏱️  3 min read

written by

kanya shah

Dalia Savy

dalia savy

Dylan Black

dylan black

(editor)


What is Solubility?

The amount of solute needed to form a saturated solution at any particular temperature is the solubility of that solute at that temperature🌡️.

The solubility of one substance in another depends on:

  • The tendency of systems to become more random (by becoming more dispersed in space)

  • The relative intermolecular solute-solute energies compared with solute-solvent interactions. 

Polar and ionic solutes tend to dissolve in polar solvents, and non-polar solutes tend to dissolve in non-polar solvents. (Remember “like dissolves like”!)

There are a few solubility rules that will be helpful on the AP Exam (though all but few of these are necessary to commit to memory):

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2Fezgif.com-webp-to-jpg.jpg?alt=media&token=011b5093-84e9-46e1-9787-707d6478dd83

Image Courtesy of Quizlet

💡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.

Saturation of Solutions

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:

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2FLdZ2muX2SNaXsOuZSuJ7_Screen%20Shot%202014-10-14%20at%2012.31.04%20AM.png?alt=media&token=5ed3b6ba-cac1-4e79-9da4-23204a6cf1a7

Image Courtesy of Dynamic Science

For example, looking at a saturated solution (note, saturated is important here, we'll get to that in a moment) of 100g H2O and KCl at approximately 70C, there will be around 50g KCl dissolved in the solution.

Saturated Solutions⚖️

A saturated solution is a solution in which all possible solute has been dissolved in a solution. Once you have reached the saturation point, any additional solute (at that temperature) will fall out of solution and not dissolve. Essentially, with saturated solutions, you are on the solubility curve.

Undersaturated Solutions⬇️

Undersaturated solutions are what their name implies - a solution that has not yet reached saturation. With an undersaturated solution, you can add more solute at the current temperature that still dissolves. Like saturated solutions, an undersaturated solution can be modeled using a solubility curve, representing a point below the solubility curve.

Supersaturated Solutions⬆️

Supersaturated solutions are a type of solution where you have more solute than you can dissolve in the solvent. In order to accomplish this, a chemist heats up the solution and then adds enough solute to saturate it at that temperature, and then slowly cools it down to the temperature they need. This accomplishes a supersaturated solution that when agitated will produce crystals as the extra salt falls out of solution.

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2FIncompleteDimwittedAfricangoldencat-size_restricted.gif?alt=media&token=f1c717fd-ed39-423b-aed9-20caa60c2887

A supersaturated solution of CH3COONa, GIF Courtesy of Gyfcat

Factors Affecting Solubility

Polarity

As mentioned before, polarity has a huge effect on solubility. 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

Pressure only affects the solubility of gases. As pressure increases, solubility increases as well. This phenomenon explains why soda🥤 becomes flat overtime.

This can also be seen using Henry's Law: C = kP, or (solubility of gas in M) = (k Constant) (Partial pressure of [g] above solution). This equation is just an extra piece of information - not necessary for the AP.

For solids and liquids, pressure does not affect solubility.

Temperature

For gases only: as temperature increases, the solubility of the gas decreases. As mentioned before, as temperature increases, the solubility of liquids and solids increase as well.

👉More about this: Unit 7 later in the course!

continue learning

Slide 1 of 15
Fiveable

Join Our Community

Fiveable Community students are already meeting new friends, starting study groups, and sharing tons of opportunities for other high schoolers. Soon the Fiveable Community will be on a totally new platform where you can share, save, and organize your learning links and lead study groups among other students!🎉

Fiveable Logo

2550 north lake drive
suite 2
milwaukee, wi 53211

92% of Fiveable students earned a 3 or higher on their 2020 AP Exams.

*ap® and advanced placement® are registered trademarks of the college board, which was not involved in the production of, and does not endorse, this product.

© fiveable 2020 | all rights reserved.