Unsaturated Solutions

Unsaturated Solutions - Types and Examples of Unsaturated Solutions

Solute, Solvent, and Solution:

A solute is the component of a solution that is present in smaller quantities by weight in the solution.

A solvent is a component of a solution that is present in larger quantities by weight in the solution. It may be a solid, liquid or a gaseous substance which can dissolve any other solid, liquid or gaseous substance. This results in a solution that will be soluble in a certain amount of solvent.

A solution is a homogenous mixture that will be composed of two or more substances and can be a mixture of solids, gases or liquids.

Solute + solvent = solution

Types of solutions:

There are three types of solutions, they are as follows:

A solution is said to be saturated which cannot dissolve any more of the substance that is mixed into it. So, when a saturated solution is kept in contact with any extra amount of solute it will not get dissolved. A solution is said to be unsaturated in which all the solute dissolves into the solvent and the solvent can be either liquid or gas. It is the solution that has not reached the saturation point into which more solute can be included. A solution is said to be supersaturated when there is more dissolved solute as compared to a saturated solution. By precipitation or crystallization, the solute can easily fall out of the solution and so special conditions will be required in order to supersaturate a solution. In order to increase the solubility, more solute can be added as it helps in heating a solution. By having scratches free containers, it can help the solute from falling out of the solution.The remains of any dissolved material in a supersaturated solution can act as nucleation sites for crystal growth.

Example of unsaturated solutions:

Take sugar and water in a container. When water is added to sugar, it gets dissolved completely. The complete dissolution of sugar in the water is called dissolution. This kind of dissolution happens when water is added to sugar because here, the saturation point has not reached and as long as the sugar gets dissolved, the solution is said to be the unsaturated solution. But when the solution reaches the saturation point, even if sugar is added further, no more sugar dissolves in water.

The same thing happens in the case of salt and water. Since the salt gets completely dissolved in water, the resulting solution is called as the unsaturated solution. Few other examples like juice powders and tea powders when mixed with water and protein powder mixed with milk get dissolved completely forming an unsaturated solution.

Facts of the unsaturated solution:

  • • From the above examples, it is clear that the unsaturated solution can dissolve more solute into it until it reaches its saturation point. No more solute will get dissolved in the solvent when the solution reaches the saturation point and this solution will be called a saturated solution. Hence, all the solutions are initially unsaturated in nature and eventually, it gets converted to a saturated solution by adding a solute to it.

  • • A component of a solution that gets dissolved in solvent and present in a lesser amount in solution is called a solute. The component of a solution that is present in a greater amount and dissolves the solute in it is called the solvent. From the above example: In the case of a solution with sugar and water, sugar acts as solute and water as a solvent and the solution in which water is the solvent is called as aqueous solutions.

  • • Based on various parameters, the solution is also of various types. Based on the physical states of solutes and solvents, the solutions can be differentiated as a solid solution, liquid solution, and gaseous solution.

  • Properties of unsaturated solutions:

  • • Generally, unsaturated solutions are highly reactive than saturated solutions. For example, linseed oil, olive oil that is triglycerides, with a high amount of unsaturated fatty acids deposit quickly than those with a high amount of saturated fatty acid deposits like coconut fat.

  • • A fatty acid with a double or triple bond in a long chain of carbons will cause a curve in the chain of carbons.

  • • Some of the hydrocarbons prevent rotation of the atoms about the bond by locking them into specific structural formations.

  • Factors affecting saturation:

    With an increase in temperature, the solubilities of ionic solutions increase with the expectations of compounds containing anions.

    In order to have greater solubilities, the solids must be finely divided.

    Concentration builds at the surface of the solute causing higher crystallization in a still solution so by maximizing the net dissolving rate, stirring the solution prevents the build up.

    Depending primarily on the temperature, the rate of crystallization will depend on the concentration of the solute at the crystal surface in contrast to the solubility rate.

    The solution will be saturated and the dynamic equilibrium can be reached if the solubility and crystallization rates are the same. Dissolving rate minus the crystallization rate is defined as the net dissolving rate.

    Degrees of Unsaturation:

    The compounds which contain double bonds are said to be unsaturated organic compounds and the compounds that contain no multiple bonds are said to be the saturated organic compounds. The saturated molecules have both sigma and pi-bond and thus due to the presence of pi- bond is the unsaturation.

    Usually, in olefins that with a double bond, acetylenes with triple bonds, and cyclic molecules unsaturation occurs. In the presence of catalysts, unsaturated compounds will be able to react with hydrogen.

    Saturation is shown with the presence of a single bond in a molecule whereas the unsaturation is introduced by the presence of multiple bonds and the degree of unsaturation will show the number of Pi- bonds.

    Example: In ethane (C2H6), which comes under alkanes contains only sigma bond and it is shown below:

  • 1. Alkanes:

  • It is saturated and contains seven single sigma bonds with molecular formula C2H6.

  • 2. Alkenes:

  • In ethane (C2H4), the presence of one double bond and four sigma bonds can be shown by the structure of ethane which is represented below.

    As each double bond has one pi- bond and one sigma bond, the presence of even one pi- bond will make the molecule of ethane an unsaturated one. They have different shapes, they can form branched chains or straight chains or rings. Alkenes having different shapes are called isomers but have the same atoms. Larger alkenes have lower melting and boiling points where smaller alkenes have high melting and boiling points and so at room temperature, they are gaseous in nature.

  • 3. Alkynes:

  • In ethyne (C2H2) which comes under alkynes, it contains one triple bond and two single bonds. It is depicted below:

    The ethyne triple bond has one sigma bond and two pi- bonds and thus this represents the unsaturation. Since there are two pi- bonds in alkynes, it introduces two degrees of unsaturation. They are also referred to as acetylene and they can form either branched or straight chains and they rarely happen in ring shapes.

    The number of hydrogen atoms decreases by two when each new pi- bond is introduced in the molecule.

    Cyclic molecule:

    In cyclic molecules like cyclopropane, its chemical formula is C3H6 which is like propene's formula C3H6. Here, there is no pi- bond and so it is introduced to one-degree unsaturation.

    Below are the representation of cyclopropane and propene respectively, which are similar in structure:

    The formula to calculate the degree of unsaturation:

    For a molecule, the degree of unsaturated can be calculated using the formula given below:

    The degree of unsaturation = number of total double bonds + (2 × number of total triple bonds) + ( total number of rings)
    When it comes to isomers that have the same molecular formula will have the same degree of unsaturation of a particular molecule’s isomers. In this case, the degree of unsaturation can be calculated by:

    Degree of unsaturation = [2 + {2 × number of carbon molecules} + number of nitrogen molecules – number of hydrogen molecules – number of halogen molecules]/ 2

    As per the formula, ethane has one degree of unsaturation. Because here, the number of carbon molecules = 3and the number of hydrogen molecules = 6

    Hence, [2 + {2 ×} – 6]/ 2 = 1 is the degree of unsaturation.

    Unsaturated Hydrocarbons:

    The unsaturated hydrocarbons are those, aliphatic hydrocarbons where there is a double or triple bond between the carbon atoms. Because of the incompletely filled valence of carbon, they are called unsaturated.

    In order to give saturated molecules, they can undergo an addition reaction with atoms or groups. In alkenes and alkynes, the carbon atom is sp²/ sp hybridized. The structure of alkyne is linear and the structure of alkene is trigonal. Examples of unsaturated hydrocarbons are acetylene, ethylene, isobutene etc.