There are many ways to measure the amount of solute present in a solution. Each method is useful for a different purpose in chemistry, so we're unfortunately stuck with the task of learning all of them. Without further ado, here they are:
Qualitative Concentrations
The amount of solute present in a solution can be described without numbers by one of the following terms:
- Unsaturated: "Unsaturated" refers to any solution that is still capable of dissolving more of a solute. For example, a glass of iced tea is not saturated with sugar if you've placed one tablespoon of sugar in it because it's still capable of dissolving more sugar. This term isn't very good for determining the exact quantity of solute present—for example, both a glass of water and a filled swimming pool would be said to be unsaturated salt solutions if there were one gram of salt dissolved in each.
- Saturated: These solutions have dissolved the maximum possible amount of solute. For example, if you keep adding sugar to a glass of Kool-Aid, it will eventually stop dissolving and settle to the bottom (little kids, however, refuse to believe this). This solution is said to be saturated.
- Supersaturated: These solutions are those that have dissolved more than the normal maximum possible amount of solute. These solutions are unusual and aren't very stable. For example, the addition of a small mote of dust to such a solution causes enough of a disturbance that crystals spontaneously form until the solution reaches a saturated state.
It's easy to tell if a solution is unsaturated, saturated, or supersaturated by adding a very small amount of solute. If the solution is unsaturated, the solute will dissolve. If the solution is saturated, it won't. If the solution is supersaturated, crystals will very quickly form around the solute you've added.
Molarity (M)
When reading the definitions of the following methods of determining concentration, pay close attention to whether the volume component asks for the weight or volume "of solution" or weight or volume "of solvent." When the weight or volume of the solution is specified, it means that you're interested in the amount of solution present after the solute has been added. If the weight or volume of the solvent is specified, this means that you're interested in the amount of solvent before the solute has been added.
Molarity is probably the most commonly used way of measuring concentration and is defined as the number of moles of solute per liters of solution.
Problem 1: What is the molarity of a solution with a volume of 3.0 liters that contains 120 grams of acetic acid (C2H3O2H)?
Let's say that we have made a solution by adding water to 40 grams (1.0 mole) of sodium hydroxide until the final volume of the solution is one liter (to review mole calculations, head back to The Mole). Because we have one mole of solute in one liter of solution, the molarity is equal to (1 mole)/(1 liter) = 1 M. We refer to a solution with a molarity of one as being a "one molar" solution.
Molality (m)
Molality is defined as the number of moles of solute per kilogram of solvent. For example, if we were to add two kilograms of water to 4 moles of sugar, the molality would be equal to 4 moles/2 kilograms = 2 m ("two molal"). When doing calculations with molality, note that because the density of water is 1.0 g/mL under standard conditions, the number of kilograms of water is equal to the number of liters of water.
Normality (N)
The normality of a solution is defined as the number of moles of a reactive species, usually referred to as "equivalents" per liter of solution. The use of "equivalents" will depend on the reaction being performed, so some knowledge of the specific chemical process in a reaction is necessary before computing normality. At least, that's the "normal" way of solving this problem. (I couldn't resist.)
Mole Fraction ()
Problem 2: What is the mole fraction of water in a solution made by mixing 4.5 moles of isopropanol with 15.0 moles of water?
The mole fraction is defined as the number of moles of one component in a solution divided by the total number of moles of all components in the mixture. In equation form, we can express the mole fraction of one component in a solution as being:
- A = moles of Amoles of A + moles of B + moles of C + …
where A refers to the first component, B refers to the second component, and C refers to the third component. As the "…" indicates, this calculation can be extended to include any number of components in the mixture.
Parts Per Million (ppm) and Parts Per Billion (ppb)
Both parts per million and parts per billion are units of concentration most frequently used in environmental analysis. Because the solvent used is most frequently water, the concentration of a solution in ppm can be found by dividing the number of mg (0.001 g) of solute by the number of liters of water. Parts per billion can be determined by dividing the number of g (10-6 g) of solute by the number of liters of water.
A Quick Summary of Units of Concentration
The following table includes all of the units of concentration we've mentioned in this section, as well as how to find them.
| molarity | M | moles of solute / liters of solution |
| molality | m | moles of solute / kilograms of solution |
| normality | N | "equivalents," which varies depending on the reaction being performed |
| mole fraction | moles of Amoles of A + moles of B + … | |
| parts per million | ppm | mg solute/L of water |
| parts per billion | ppb | g solute/L of water |
Excerpted from The Complete Idiot's Guide to Chemistry © 2003 by Ian Guch. All rights reserved including the right of reproduction in whole or in part in any form. Used by arrangement with Alpha Books, a member of Penguin Group (USA) Inc.
To order this book direct from the publisher, visit the Penguin USA website or call 1-800-253-6476. You can also purchase this book at Amazon.com and Barnes & Noble.
A solution is a liquid phase of matter that is formed by dissolving a solute in a solvent. A solution can be converted into a saturated solution by adding more solutes until no more solutes can be dissolved. A concentrated solution contains a considerably high amount of solutes, but that amount is not the maximum. The key difference between saturated and concentrated solution is that additional solutes cannot be dissolved in a saturated solution since it contains the maximum amount of solutes whereas additional solutes can be dissolved in a concentrated solution because it does not contain the maximum amount of solutes (not saturated with the solute).
CONTENTS
1. Overview and Key Difference
2. What is Saturated Solution
3. What is Concentrated Solution
4. Similarities Between Saturated and Concentrated Solution
5. Side by Side Comparison – Saturated vs Concentrated Solution in Tabular Form
6. Summary
What is Saturated Solution?
A saturated solution is a chemical solution containing the maximum concentration of a solute dissolved in the solvent. Additional solutes cannot be dissolved in a saturated solution since it contains the maximum amount of solutes. The opposite form of the saturated solution is the unsaturated solution. The unsaturated solution is not saturated with the solute. An unsaturated solution can be either a concentrated solution or a dilute solution.
There are several factors that affect the saturation of a solution. These factors affect the dissolution of solutes in the solvent.
- Temperature – The solubility of solid compounds increases with increasing the temperature of the solvent. Therefore, more solutes can be dissolved in the hot solvent rather than in the cold solvent.
- Pressure – More solutes can be forces to get dissolves in the solvent by applying pressure. Hence, the dissolution of solutes can be increased by increasing the pressure of the system. Ex: Gases.
- Chemical composition – If some other solutes are already present in the solution, it affects the solubility of solutes.
A saturated solution can be produced by adding a solute to the solvent until no more solutes are dissolving. Or else, it can be done by evaporating the solvent of solution until solute starts to form crystals. Another method, though not that much common is to add seeds of crystals to a supersaturated solution. A supersaturated solution contains many solutes that stay dissolved even if the solution is cooled. When seeds of crystals are added to this supersaturated solution, the solutes starts to crystallize, giving a saturated solution.
Figure 01: Sparkling Juices are Saturated Solutions
Some examples of saturated solutions include carbonated water (saturated with carbon), saturated sugar solutions (no more sugar can be dissolved), beer or sparkling juices are saturated with carbon dioxide, etc.
What is Concentrated Solution?
A concentrated solution is a chemical solution containing a high amount of a solute dissolved in the solvent. Additional solutes can be dissolved in a concentrated solution because it does not contains the maximum amount of solutes (not saturated with the solute). The opposite form of the concentrated solution is dilute solution. A dilute solution contains a relatively low amount of solutes dissolved in a solvent.
Figure 02: A concentrated solution (right) has a strong colour compared to a diluted solution (left)
The concentrated solutions of acids or bases are recognized as strong acids or strong bases. In contrast, dilute acids or bases are weak acids or bases. The term concentrated is used to give a quantitative idea about a solution. A concentrated solution can be formed by dissolving more solutes into a solution or by evaporating a solution until a considerable amount of solvent is evaporated leaving solutes in the solution. The concentration of a solution can be given as below. There the concentration is given by the unit mol/L.
Concentration = number of moles of solutes / volume of the solution
What are the Similarities Between Saturated and Concentrated Solution?
- Both Saturated and Concentrated Solution are solutions containing a high amount of solutes
- Both Saturated and Concentrated Solution terms express a quantitative idea about solutions.
What is the Difference Between Saturated and Concentrated Solution?
| A saturated solution is a chemical solution containing the maximum concentration of a solute dissolved in the solvent. | A concentrated solution is a chemical solution containing a high amount of a solute dissolved in the solvent. |
| Amount of Solutes | |
| Saturated solution contains the maximum amount of solutes that it can hold. | Concentrated solution contains a considerably high amount of solutes. |
| Addition of More Solutes | |
| Additional solutes cannot be dissolved in a saturated solution since it contains the maximum. | Additional solutes can be dissolved in a concentrated solution because it does not contains the maximum amount of solutes (not saturated with the solute). |
| Opposite Form | |
| The opposite form of saturated solution is unsaturated solution. | The opposite form of concentrated solution is dilute solution. |
| Examples | |
| Some examples of saturated solutions include carbonated water, saturated sugar solutions, beer or sparkling juices are saturated with carbon dioxide, etc. | Some examples of concentrated solutions include concentrated acids and concentrated bases used in laboratories. |
A saturated solution is a form of a concentrated solution, but it contains the maximum amount of solutes that can hold. The difference between saturated and concentrated solution is that additional solutes cannot be dissolved in a saturated solution since it contains the maximum amount of solutes whereas additional solutes can be dissolved in a concentrated solution because it does not contain the maximum amount of solutes (not saturated with the solute).
Reference:1.“13.2: Saturated Solutions and Solubility.” Chemistry LibreTexts, Libretexts, 8 Oct. 2017. Available here 2.“How to Concentrate a Solution.” Sciencing. Available here
3.Helmenstine, Anne Marie, D. “Saturated Solution Definition and Examples.” ThoughtCo, Jun. 20, 2017. Available here
Image Courtesy:1.’2980956′ by Nicole_80 (Public Domain) via pixabay
2.’RiboflavinSolution’By Sbharris – Own work, (CC BY-SA 3.0) via Commons Wikimedia