When is a solution saturated

Suppose that you have a beaker of water to which you add some salt, stirring until it dissolves. So you add more and that dissolves.

You keep adding more and more salt, eventually reaching a point that no more of the salt will dissolve no matter how long or how vigorously you stir it. On the molecular level, we know that action of the water causes the individual ions to break apart from the salt crystal and enter the solution, where they remain hydrated by water molecules.

What also happens is that some of the dissolved ions collide back again with the crystal and remain there. Recrystallization is the process of dissolved solute returning to the solid state. At some point the rate at which the solid salt is dissolving becomes equal to the rate at which the dissolved solute is recrystallizing. When that point is reached, the total amount of dissolved salt remains unchanged.

Solution equilibrium is the physical state described by the opposing processes of dissolution and recrystallization occurring at the same rate.

The solution equilibrium for the dissolving of sodium chloride can be represented by one of two equations. While this shows the change of state back and forth between solid and aqueous solution, the preferred equation also shows the dissociation that occurs as an ionic solid dissolves.

If the molecule or ion happens to collide with the surface of a particle of the undissolved solute, it may adhere to the particle in a process called crystallization. Dissolution and crystallization continue as long as excess solid is present, resulting in a dynamic equilibrium analogous to the equilibrium that maintains the vapor pressure of a liquid.

We can represent these opposing processes as follows:. Although the terms precipitation and crystallization are both used to describe the separation of solid solute from a solution, crystallization refers to the formation of a solid with a well-defined crystalline structure, whereas precipitation refers to the formation of any solid phase, often one with very small particles.

The maximum amount of a solute that can dissolve in a solvent at a specified temperature and pressure is its solubility. Even for very soluble substances, however, there is usually a limit to how much solute can dissolve in a given quantity of solvent. In general, the solubility of a substance depends on not only the energetic factors we have discussed but also the temperature and, for gases, the pressure.

A solution with the maximum possible amount of solute is saturated. If a solution contains less than the maximum amount of solute, it is unsaturated. Using the value just stated, a saturated aqueous solution of NaCl, for example, contains We can prepare a homogeneous saturated solution by adding excess solute in this case, greater than Because the solubility of most solids increases with increasing temperature, a saturated solution that was prepared at a higher temperature usually contains more dissolved solute than it would contain at a lower temperature.

Like a supercooled or superheated liquid, a supersaturated solution is unstable. Consequently, adding a small particle of the solute, a seed crystal, will usually cause the excess solute to rapidly precipitate or crystallize, sometimes with spectacular results.

In contrast, adding a seed crystal to a saturated solution reestablishes the dynamic equilibrium, and the net quantity of dissolved solute no longer changes. Needle crystal is truly wonderful structures. The amount of heat released is proportional to the amount of solute that exceeds its solubility.

The interactions that determine the solubility of a substance in a liquid depend largely on the chemical nature of the solute such as whether it is ionic or molecular rather than on its physical state solid, liquid, or gas. We will first describe the general case of forming a solution of a molecular species in a liquid solvent and then describe the formation of a solution of an ionic compound.

The London dispersion forces, dipole—dipole interactions, and hydrogen bonds that hold molecules to other molecules are generally weak. Even so, energy is required to disrupt these interactions. As described in Section Consequently, the only way they can interact with a solvent is by means of London dispersion forces, which may be weaker than the solvent—solvent interactions in a polar solvent. It is not surprising, then, that nonpolar gases are most soluble in nonpolar solvents.

As a result, nonpolar gases are less soluble in polar solvents than in nonpolar solvents. This is precisely the trend expected: as the gas molecules become larger, the strength of the solvent—solute interactions due to London dispersion forces increases, approaching the strength of the solvent—solvent interactions.

Virtually all common organic liquids, whether polar or not, are miscible. If the predominant intermolecular interactions in two liquids are very different from one another, however, they may be immiscible. Just because two liquids are immiscible, however, does not mean that they are completely insoluble in each other. For example, mg of benzene dissolves in mL of water at Only the three lightest alcohols methanol, ethanol, and n-propanol are completely miscible with water.

Study Materials. Why use Doubtnut? Instant Video Solutions. Request OTP. Updated On: Share This Video Whatsapp. All rights reserved. Understanding Saturated Solutions So what is a saturated solution? Elements that affect a solution's saturation include: the solution's temperature warmer solution is more soluble the solution's pressure the chemical makeup of substances involved the concentration and amount of solute You can create a saturated solution by: adding solute to liquid until dissolving stops evaporating a solvent from a solution until the solute begins to crystallize or precipitate adding seed crystals to a solution that is supersaturated Once the solute stops dissolving, the solution is saturated.

Everyday Examples of Saturated Solutions There are saturated solution examples all around you! Saturated Solution Examples in the Home Have you ever added too much chocolate powder to your chocolate milk?

Outdoor Saturated Solution Examples Like all elements of nature, outdoor solutions tend to find balance in their natural state. A few examples of saturated solutions in nature are: seawater - seawater is already saturated with salt; additional salt forms solid salt crystals instead of dissolving soil - the Earth's soil is saturated with nitrogen freshwater - most elements and metals, including potassium, can saturate freshwater air - the air we breathe is saturated with moisture; when there is excess moisture, it becomes dew or mist The outdoor temperature can affect the solubility of these solutions.

Unsaturated Solutions and Supersaturated Solutions Solutions that aren't saturated are either unsaturated solutions or supersaturated solutions.

These solutions can be defined in the following ways: unsaturated solutions - dissolved solute is below the saturation point for example, water with just a pinch of salt or coffee with only one packet of sugar supersaturated solutions - dissolved solute is more than the saturation point for example, water with a cup of salt added or coffee with ten packets of sugar A bottle of soda is a good way to visualize unsaturated, saturated and supersaturation solutions.