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solution is a homogeneous or heterogeneous mixture

RELATIVE PROPORTION OF SOLUTION:  HOW TO EXPLAIN ITS

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RELATIVE PROPORTION OF SOLUTION

INTRODUCTION

Solution is a homogeneous mixture of two or more substances which contains fixed amount of constituents as relative proportion in solution. The amount may vary time to time. The component present in greater amount is solvent. It dissolves the other component.  Most of the time it may be liquid or gaseous. The solution has same physical state as that of the solvent. The component of the solution present in lesser amount is solute. It easily mixes in solvent.

PROPERTIES OF A SOLUTION

  • Solution is always homogeneous in nature.
  • Particles of a solution  are very small in size , as less than 1nm. We cannot see these particles in naked eye.
  • Particles do not scatter a beam of light passing through the solution. So, we cannot see the path of light in the solution.
  • Solute particles do not settle down even in undisturbed state. So mixture is stable always.
  • We can not separate the solute particles by filtration.

CONCENTRATION OF A SOLUTION

We term concentration in relative proportion in solution as the amount of solute present in a given mass or volume of a solution. The relative proportion in solute and  solvent may vary. We classify the solution according to the amount of solute present in a given amount of solvent.

  • Saturated solution: In this mixture we cannot dissolve extra amount of solute at a given temperature. The amount of the solute present in the saturated solution at this temperature  we term as SOLUBILITY.

Solubility => {(mass of the solute)/ (mass of solvent)} X 100

  • Unsaturated solution : In this mixture, amount of solute is less than the saturation level.

Concentration of solution => {(amount of solute)/ (amount of solution)} X 100

SUSPENSION IN RELATIVE PROPORTION IN SOLUTION

It is a heterogeneous mixture in which solute particles do not dissolve. The particles are suspended through out the mixture.

PROPERTIES OF SUSPENSION

  • It is heterogeneous in nature.
  • We can notice the particles in naked eye.
  • Suspension can show Tyndall effect by passing the beam of light. In this way we can see the path of light.
  • The solute particles settle down when we keep the mixture undisturbed.
  • We can separate the particles by filtering.
  • In suspension the dissolving solvent we term as medium.

EXAMPLES

HOMOGENEOUS MIXTURE:  Sugar water mixture, Tincture of iodine, Soda water, Alloy etc.

HETEROGENEOUS MIXTURE: Mixture of chalk and water, Sand and water mixture, Smoke.

COLLOID

It is a mixture that is actually heterogeneous, but appears as homogeneous. Here particles spread uniformly throughout the mixture. Milk, Cheese, Shaving cream are the examples of colloidal sol.

PROPERTIES OF A COLLOID

  • It is a heterogeneous mixture.
  • The size of particles is very small, so we cannot see these in naked eyes.
  • Colloidal particles can scatter beam of light, so we can see the path of light.
  • Particles do not stable if kept undisturbed.
  •  Colloidal particles can pass through filter paper. Therefore, we cannot separate these through filter paper.
  • By centrifugation we can separate the particles.

COMMON EXAMPLES OF COLLOIDS

TYPES OF COLLOIDDISPERSED PHASEDISPERSION MEDIUMEXAMPLES
AerosolLiquidGASFog, cloud, mist
AerosolSolidGASSmoke, automobile exhaust.
FoamGasLIQUIDShaving cream.
EmulsionLiquidLIQUIDMilk, face cream.
SolSolidLIQUIDMilk of magnesia, mud.
FoamGasSOLIDFoam, rubber, sponge, pumice.
GelLiquidSOLIDJelly, cheese, butter.
Solid solsolidSOLIDMilky glass, colored gemstone.

 SHORT TYPE QUESTION ON MIXTURE IN RELATIVE PROPORTION IN SOLUTION

Qs1: Name the effect shown by suspension.

Ans1: Suspension shows the property of Tyndall effect because the particles are very large and scatter light.

Qs2: Why particles in a true solution we cannot see in naked eyes?

Ans2: Particles of a true solution are very small in size (1nm) , that is why we cannot see the particles in naked eyes.

Qs3: While diluting a solution of salt in water, a student by mistake added acetone (boiling point 56°C). Explain the technique by which we can separate acetone from water.

 Ans3:  We get back acetone from the solution by simple distillation. The boiling point of water is 100° C, while boiling point of acetone is 56°C. The difference between the boiling point of these two compounds is 44 K. if the difference is more than 25 K then we can separate these mixture by simple distillation method. In case of difference of less than 25 K then the process will be fractional distillation.

ANWER IN BRIEF

Qs4: All solutions are mixtures but all mixtures are not solutions. Justify.

Ans4: If a mixture of two or more substances is homogeneous in nature and their composition can be varied only within a certain limit, then the mixture we term as solution. Example common salt dissolved in water forms a solution .

However, a mixture may also be heterogeneous in nature, in which the composition is not uniform throughout and can be changed in any proportion. This type of mixture cannot be solution. Example a mixture of sand and sugar cannot be solution.

That is why, all solution are mixtures but all mixtures are not solutions as per relative proportion in solution.

Qs5: What is dispersion medium and dispersed phase of a colloidal solution?

Ans5: The medium in which the colloidal particles remain uniformly dispersed we term as dispersion medium.

The component of a colloidal solution which remain uniformly dispersed in the dispersion medium. This medium consists of particles with diameter ranging from 10-5 to 10-7 cm which we term as dispersion phase.

Example: In a gold sol, water is the dispersion medium while gold particles from the dispersed phase.

HIGHER ORDER THINKING SKILL

Qs6: Why do colloidal solutions formed by different methods exhibit different colors?

Ans6: The color of a colloidal solution depends on the wavelength of visible light scattered by the colloidal particles. The scattering of light depends on the size of colloidal particles formed is different for different methods. So, a colloidal solution exhibits different colors when formed by different methods.  

Qs7: What are alcosol and hydrosol?

Ans7: Colloids with alcohol as dispersion medium and having solids as dispersed phase we term as alcosol.

Colloids whose dispersed phases and dispersion medium are solid and water respectively we term as hydrosol.

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