Unsaturated Solutions: Solubility, Types, Properties, Examples

Unsaturated Solutions refers to those chemical solutions where the concentration of the dissolved solute is less than the solubility equilibrium (saturation point of solvent at that specific temperature gradient). If the amount of dissolved solute is the same as the solvent’s saturation point, it is said to be a saturated solution. 

Keyterms: Solutions, dissolved solute, solubility equilibrium, saturation point, solvent, saturated solution, homogeneous mixture, solvent

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What is a Solution?

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A Solution is a kind of homogeneous mixture in which the distribution of the components is uniform (evenly distributed). For instance, saltwater is a solution, because the dissolved salt is evenly distributed throughout the entire saltwater sample. 

Components of a Solution

Generally, Solutions have two types of constituents: solvent and solute. The component which is dissolved in another component is called a solute, and the component which dissolves the solute is called a solvent. 

Mostly the solvent is present in a major proportion than the solute, and the amount of solute is lesser than the solvent. Both solute and solvent of a solution exist in any one of the three states (or phases) of matter i.e. solid, liquid, and gas. To understand much better let us look at the examples of solute and solvents in some solutions below: 

• Air around us is a homogenous mixture of gases because both the solvent and the solute in it are gases.
• Lemon water is a solution in which lemon juice is dissolved in water. Here, water is said to be the solvent, and lemon juice is said to be the solute. 
• Tincture of Iodine is a solution of Iodine in alcohol. Iodine is the solute whereas alcohol is the solvent.
• Coffee is a solution of coffee powder, sugar, and milk. In this coffee powder and sugar are solutes, and milk is the solvent. 
• Water is said to be the "universal solvent" as it can dissolve more substances than any other liquid available on Earth.

Solubility of a Solution

The amount of solute that can be dissolved in a solvent is called its solubility. In other words, the ability of a substance to dissolve is called its solubility. Solids such as sugar and salt are more or quickly soluble in hot water than in cold water. However, gases such as carbon dioxide and oxygen are more soluble in cold water than in hot water.

For solutions with components in the same phase, the substances present in lower concentrations are solutes, while the substance present in the highest abundance is the solvent. If we take air as an example, oxygen and carbon dioxide gases are solutes, while nitrogen gas is the solvent.

Saturation of a Solution

The term Saturation of a solution can be defined as the maximum point at which a solvent can dissolve no more of solute. This saturation point (the point of maximum concentration), depends on the temperature present in the liquid as well as the chemical nature of the substances that take part. 

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Unsaturated Solution

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An unsaturated solution is a type of solution that completely dissolves, leaving no remaining substances. They have less solute than the solvent. 

For instance, adding a salt or sugar solute into water (solvent) and stirring it, forms an unsaturated or saturated, or supersaturated solution, depending on the quantity (or amount) of solute that is added to the solvent. When a small amount of solute is added into the solvent until it is dissolved completely, then it forms an unsaturated solution. 

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Examples of Unsaturated Solutions

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If a spoonful of sugar is added to a hot cup of coffee or tea, it produces an unsaturated solution

Vinegar is nothing but an unsaturated solution of acetic acid in water. 

Mist is an unsaturated solution of water vapor in the air.

0.01 M HCl is an unsaturated solution of hydrochloric acid in water.

Iced coffee is an unsaturated solution of ice, sugar, coffee granules, and milk 

Tea and the sugar solution is a good example of an unsaturated solution.

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Properties of Unsaturated Solutions

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• Unlike saturated solutions, unsaturated solutions are highly reactive. 
• A fatty acid with a double or triple bond can cause a curve in the long carbon chain.
• For example, with a high amount of unsaturated fatty acids, linseed oil, triglyceride olive oil is rapidly deposited, when compared to those with a high amount of saturated fatty acid deposits such as coconut fat.
• Some Hydrocarbons prevent the rotation of the atoms about the bond by locking them into specific structural formations.

The concentration or percentage of solute in an unsaturated solution is much lower than its solubility equilibrium. 

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Factors Affecting Saturation

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There are varieties of factors that show the effect on the saturation of a solution. 

The amount of solute that can be dissolved in a solvent to form a saturated solution depends on a variety of factors. The most important factors are:

Temperature 

With the rise of temperature, the solubility of solvent increases. For example, salt can be dissolved in hot water much more than in cold water.

Pressure

By increasing the pressure in the solution, more amount of solute can be added to a solvent. This process is more widely used to remove liquid gases.

Chemical Composition

Solubility depends on the nature of the solute and solvent and the action of other impurities in a solution. For instance, in water, you can dissolve much more sugar than salt. Ethanol (a colorless and volatile flammable liquid) and water are mutually completely soluble.

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Things to Remember

• Unsaturated Solutions are Chemical Solutions where the amount of dissolved solute is lower than the saturation point of the solvent. 
• A Solution is a kind of homogeneous mixture where the components are distributed evenly. 
• A Solution is made of a Solute and a Solvent
• The amount of solute that can be dissolved in a solvent is called its solubility.
• The term Saturation of a solution can be defined as the maximum point at which a solvent can dissolve no more of solute.
• An unsaturated solution is a type of solution that completely dissolves, leaving no remaining precipitate.
• Some unsaturated solutions are highly reactive.
• The factors that affect Saturation are: Temperature, Pressure and Chemical Composition. 

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Previous Year Questions

1. To observe an elevation of boiling point of 0.05^oC, the amount of solute (Mol. Wt.=100) to be added to 100g of water (Kb=0.5) is
2. If vapour pressure of pure water is p1∘1 the vapour pressure of solution is
3. The temperature at which osmotic pressure is measured, is (R is gas constant)
4. Which of the following statement is true ?
5. The ionic strength of a solution containing 0.1 mole/kg of KCl and 0.2 mole/kg of CuSO4 is​
6. Solubility of which among the following solids in water changes slightly with temperature ?​
7. How many gram-equivalents of NaOH are required to neutralise 25cm3 of a decinormal HCl solution?​
8. Identify the correct statement regarding the elevation of boiling point (b.pt) of the resulting solutions.
9. What is the mole fraction of toluene in vapour phase when 117g of benzene is mixed with 46g of toluene ?
10. The volumes of two HCl solutions A(0.5 N) and B(0.1 N) to be mixed for preparing 2 L of 0.2 N HCl solution are​
11. If the coordination number of aluminium in �X � is 6, the correct formula of X is
12. Dissolving 120g of a compound (mol. wt =60) in 1000g of water gave a solution of density 1.12gmL−1. The molarity of solution is​
13. Equal weights of NaCl and KCl are dissolved separately in equal volumes of solutions. Molarity of the two solutions will be :
14. Which of the following solutions is an example of negative deviation from Raoult’s law?​
15. Which of the following sets of solutions of urea (mol. mass 60gmol−1) and sucrose (mol. mass 342gmol−1) is isotonic?​
16. What is the mole fraction of the solute in 2.5 molal aqueous solution?…..[AMUEEE 2015]
17. Boiling point of pure benzene =80.1∘C and Kb=2.53Kmol−1kg….[JKCET 2017]
18. What will be the freezing point of 1% solution of glucose in water, given that molal depression constant for water is 1.84Kmol−1….[JKCET 2013]
19. When a solution containing non-volatile solute is diluted with water…...[JKCET 2011]
20. Which of the following is an example of Maximum boiling azeotrope?..[AMUEEE 2011]​