Honey is a fascinating solution, made up of approximately 70% sugar and 20% water. Honey contains more sugars than what would normally dissolve at room temperature, and it is considered a supersaturated solution!
So, if you are interested in learning about unsaturated, saturated, and supersaturated solutions, you came to the right place!
- This article is about saturated, unsaturated and supersaturated solutions.
- First, we will look at the basics of solubility and state the definitions of saturated, unsaturated, and supersaturated solutions.
- Then, we will learn how to tell whether a solution is saturated, unsaturated, and supersaturated based on solubility curves.
- Next, we will make a table showing the differences between these three types of solutions.
- Lastly, we will explore some examples of saturated, unsaturated, and supersaturated solutions.
Saturated Unsaturated and Supersaturated Solutions Definition
Let's start our journey into the world of saturated, unsaturated, and supersaturated solutions by reviewing the term solubility.
Solubility is referred to as the amount of solute that can dissolve in a solvent at a given temperature.
When a solute dissolves in a solvent due to the attraction between their particles, a solution is formed.
$$ \text{Solute + Solvent} \longrightarrow \text{Solution} $$
Chemists rely on solubility to determine a solute's ability to dissolve in a solvent, and the most important rule in solubility is that "like dissolves like". But, what does this mean? Let's find out!
If we had a polar solvent like water (H2O), we would expect polar solutes (ex. sugars) or ionic solutes (such as ionic salts) to be able to dissolve and form a homogenous mixture (solution). On the other hand, nonpolar solutes like fats and oils cannot dissolve in polar solvents, and is the reason we see separate layers when we add oil to water! Nonpolar solutes can only dissolve into nonpolar solvents like hexane (C6H6) because they lack charge and therefore cannot mix with ionic and polar substances.
- Nonpolar solvents include fats, steroids, waxes, benzene, hexane, and toluene.
- Polar solvents include sugar, inorganic salts, water, small alcohols, and even acetic acid.
- Nonpolar solvents dissolve nonpolar solutes.
- Polar solvents dissolve polar solutes.
For an in-depth explanation on polar and non polar solutes, check out "Solubility"!
Solutions are classified into saturated, unsaturated, and supersaturated based on the amount of solute added to a solvent, and whether all the solute was dissolved in the solvent. So, let's dive into saturated, unsaturated, and supersaturated solutions and look at their definitions!
The first type of solution we will talk about are unsaturated solutions.
In unsaturated solutions, less than the max. amount of solute is dissolved into the solvent.
When you have an unsaturated solution, it means that you added an amount of solute that is less than the maximum amount that is able to dissolve in the solvent, and then if you decided to add more solute to it, it will still dissolve, up to a certain point.
For example, the solubility of sodium chloride (NaCl) in water (H2O) is around 36 grams of NaCl per 100 grams of water at 30 °C. So, if you have 100 grams of water, and you add less than 36 grams of the solute NaCl to it, then it will be considered an unsaturated solution!
Now, if you added exactly 36 grams of NaCl to 100 grams of H2O, then you would have a saturation solution in front of you.
A saturated solution is a solution that possesses the maximum amount of solute that can be dissolved per given amount of solvent at a certain temperature.
The third type of solution is a supersaturated solution, and it involves increasing a solution's temperature and then cooling it down in order to dissolve more than the maximum amount of solute in it.
A supersaturated solution is referred to as a solution that contains more than the maximum amount of solvent dissolved in a certain amount of solute.
Supersaturated solutions are very unstable, and with time, crystals may form.
Sometimes, the solubility of a solution can change (increase or decrease) depending on temperature. For many solids dissolved in water, the solubility increases as temperature increases. Increasing the temperature increases the kinetic energy (K.E.) of both the solute and the solvent molecules, allowing the solvent molecules to break apart the solute molecules so that the solute molecules can dissolve more readily.
For gases, on the other hand, solubility decreases with increasing temperature. The image below shows the solubility curve for some solutes in 100 grams of H2O.
Figure 2. Solubility curve graph, Isadora Santos - Vaia Originals.
How to Tell if a Solution is Saturated, Unsaturated, or Supersaturated?
There is an easy way to tell if a solution is saturated, unsaturated, or supersaturated based on the solubility curve (figure 2).
For example, the solubility curve for potassium chloride (KCl) tells us that the solution is saturated along the line. At 50 °C, the solubility of KCl is 43 grams per 100 grams of water (H2O). Therefore, if less than 43 grams of KCl was added to water at 50 °C, then we would consider it an unsaturated solution! Likewise, adding more than 43 grams of KCl will make it a supersaturated solution!
Figure 3. Solubility curve of KCl, Isadora Santos - Vaia Originals.
Let's look at a problem!
1) If you added 100.0 grams of KNO3 to 100 grams of H2O at 60.0 °C, would the solution be saturated, unsaturated, or supersaturated?
If you go back and look at figure 2 showing the solubility curve of different salts, notice that at 60 °C, more than 100.0 grams of KNO3 is needed to make a saturated solution. Therefore, this solution would be considered unsaturated.
2) How many grams of KNO3 would be needed to make a saturated solution in 300 grams of H2O at 20.0 °C?
At 20.0 °C, around 35 grams of KNO3 are required to saturate 100 grams of H2O. So, to saturate 300 grams of water, we would need 105 grams of KNO3.
$$ \frac{300\text{ g H}_{2}\text{O }\times \text{ 35 g KNO}_{3}}{100\text{ g H}_{2}\text{O}} = 105 \text{ g KNO}_{3} $$
Difference between Saturated Unsaturated and Supersaturated Solutions
The best way to look at the difference between saturated, unsaturated and supersaturated solutions is by making a table.
Unsaturated Solution | Saturated Solution | Supersaturated Solution |
When the solute dissolved in the solvent at a certain temperature is less than the maximum amount. | A solution containing the maximum amount of solute dissolved in the solvent at a particular temperature. | A solution containing more solute than the maximum amount dissolved in a solvent at a given temperature. |
In a solubility curve, unsaturated solutions are found below the solubility curve line. | In a solubility curve, saturated solutions are found within the line. | In a solubility curve, supersaturated solutions are found above the saturated line. |
Saturated Unsaturated and Supersaturated Solutions Venn Diagrams
Now that we know the difference between these types of solutions, let's make a venn diagram to compare and contrast saturated and unsaturated solutions.
Figure 4: Venn diagram showing saturated and supersaturated solutions, Isadora Santos - Vaia Originals.
Saturated Unsaturated and Supersaturated Solutions Examples
Lastly, let's explore some examples of these solutions. Perhaps the most common example is the addition of sugar to water when making lemonade! When you start adding sugar, the sugar will dissolve, until it reaches a point where it no longer dissolves and the solution becomes saturated.
Other examples of saturated solutions include adding protein powder to milk, tea, or water until not more powder dissolves in the solvent!
But, what about unsaturated solutions? Unsaturated solutions can be formed by dissolved salt or sugar in water below the saturation point! Mist (water vapor solution) is also an example of an unsaturated solution in air.
Supersaturated solutions contain more solute than the solubility allows. Carbonated water (soda water) is an example of a supersaturated solution because carbon dioxide is present in higher amounts than usually dissolved in water due to the elevated pressure in the bottle.
Now, I hope that you feel confident in your understanding of saturated, unsaturated and supersaturated solutions!
Saturated Unsaturated and Supersaturated - Key takeaways
- Solubility is used to describe the amount of solute that can dissolve in a given solvent at a given temperature.
- An unsaturated solution is a solution that has less than the max. amount of solute dissolved in the solvent.
- A saturated solution is a solution that possesses the max. amount of solute dissolved per given amount of solvent at a certain temperature.
- A supersaturated solution is referred to as a solution that contains more than the max. amount of solvent dissolved in a certain amount of solute.
- We can tell if a solution is saturated, unsaturated, or supersaturated based on its solubility curve.
References
- Zumdahl, S. S., Zumdahl, S. A., & Decoste, D. J. (2019). Chemistry. Cengage Learning Asia Pte Ltd.
- Theodore Lawrence Brown, Eugene, H., Bursten, B. E., Murphy, C. J., Woodward, P. M., Stoltzfus, M. W., & Lufaso, M. W. (2018). Chemistry : the central science (14th ed.). Pearson.
- Swanson, J. (2021). Everything you need to ace chemistry in one big fat notebook. Workman.
- Post, R. (2020). Chemistry : Concepts and Problems, a Self-Teaching Guide. Wiley & Sons, Incorporated, John.
- Moore, J. T., & Langley, R. (2021a). McGraw Hill : AP chemistry, 2022. Mcgraw-Hill Education.
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