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Solutions

The two oceans that meet but don't mingle! The two oceans that meet but don't mingle! Ocean/sea is an aqueous solution containing dissolved salts. In the middle of Gulf of Alaska two water bodies come together but do not mingle with one another at all. A frothy foam which separates the two oceans clearly indicates this. One ocean has less concentration due to addition of fresh water from melting of icecaps. Due to the difference in concentration there is a difference in the density and surface tension of two water bodies. This surface tension acts as thin wall between the two layers and prevents mixing with each other.

Learning Objectives

After completing the topic, the student will be able to:

  • Define the terms solution, solute and solvent.
  • Differentiate solution, suspension and colloid.
  • Classify the colloids based on dispersion medium and phase.
  • Understand the solubility process and discuss the factors effecting solubility.
  • Classify the solutions based on the amount of solute and explain the effect of temperature and pressure on solubility.
  • Distinguish between ideal and non–ideal solutions.
  • Discuss colligative properties of electrolyte and non-electrolyte solutions.
  • Describe the phase diagrams and identify the invariant points.
Example of aqueous solution Example of aqueous solution Sea water is a complex aqueous solution. It consists of many dissolved substances, of which sodium chloride is in highest concentration.
Solutions

A solution is a homogeneous mixture of one substance dissolved in another so that the properties are the same throughout.

A solution is composed of a solute and the solvent. Solutions typically occur by the solute being dissolved into the solvent. The substance which is dissolved in a liquid to make a solution is called solute. The liquid in which solute is dissolved is known as solvent. Usually the substance present in lesser amount in a solution is considered as the solute, and the substance present in greater amount in a solution is considered as the solvent. The solute particles are also called ‘dispersed particles’ and solvents are also known as ‘dispersion medium’.

Examples: Sea–water, copper sulphate solution, alcohol and water mixture, petrol and oil mixture, soda water, soft drinks (Coca-cola, Pepsi etc.) and lemonade (which is a sweetened drink made from lemon juice or lemon flavoring). Salt solution is made by dissolving salt in water. So in salt solution, 'salt' is the solute and 'water' is the solvent. Similarly, the substances like sugar, ammonium chloride, copper sulfate and urea etc., which are dissolved in water to make solutions, are called 'solutes', whereas water is the 'solvent'. Solutions, suspensions and colloids differ in the size of solute particles (or dispersed particles), the size of particles being minimum in solutions and maximum in suspensions.

Copper sulfate dissolves in water to form copper sulfate solution Copper sulfate solution When blue colored copper sulfate crystals are added to a beaker containing water, it dissolves slowly. When stirred it completely dissolves to form a true solution.
Aqueous and non-aqueous solutions

Salt solution and sugar solution are true solutions (molecular solutions) because in these solutions, the particles of salt and sugar are mixed so well with water that we cannot distinguish one from the other. The substances like salt, sugar, etc., which dissolve in water completely are said to be 'soluble' in water. Only soluble substances form true solutions. Copper sulfate is soluble in water to form a true solution which is blue in color.

Water is the universal aqueous solvent. The organic liquids like alcohol, acetone, carbon tetrachloride, carbon disulphide and benzene are called non–aqueous solvents. The solutions made by dissolving various solutes in water are called aqueous solutions. On the other hand, the solutions made by dissolving solutes in organic liquids are called non–aqueous solutions.

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