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Ravela Da Cruz

HS-PS1-5

Colligative Properties Study Guide

Colligative qualities are those of a solution solely dependent on the concentration of solute molecules.

INTRODUCTION

Those in colder areas have seen the trucks spread salt on the roadways. Why? When flying in frigid weather, planes must be de-iced before take-off. Why is that the case? Pure solvents have different boiling and freezing points than solutions. All the colligative properties (like vapor pressure, boiling, and freezing temperature) and their values change by adding a solute to an existing solution.

plane-being-deiced Source

WHAT ARE COLLIGATIVE PROPERTIES?

  • Colligative qualities are those of a solution determined by the number of particles in a given volume of solvent (concentration) rather than the mass or nature of the solute particles.
  • The temperature has an impact on colligative characteristics as well.
  • Vapour pressure reduction, freezing point depression, osmotic pressure reduction, and boiling point elevation are colligative qualities.

VAPOR PRESSURE LOWERING

  • The pressure imposed by a liquid's gaseous form when vaporization and condensation happen at equal rates is known as the equilibrium vapor pressure: Liquid ⇌ gas
  • When a non-volatile chemical is dissolved in a volatile liquid, the vapor pressure of the liquid is reduced.
  • Solvent molecules have to be located at the solution's surface for it to evaporate.
  • The presence of a solute limits the accessible surface area for solvent molecules, lowering the rate of solvent vaporization.
  • Because the availability of a solute does not affect the rate of condensation, the vaporization-condensation equilibrium is attained with fewer solvent molecules in the vapor phase (i.e., at a lower vapor pressure).

Vapour pressure lowering Source

BOILING POINT ELEVATION

The temperature at which a liquid's vapor pressure equals ambient air pressure is its boiling point. Because the introduction of non-volatile solutes lowers a solution's vapor pressure, it logically follows that the solution's boiling point will rise as a result.

The elevation of the boiling point can be estimated using the equation: ΔTb = Kb*m

where,

Kb = ebullioscopy constant

m = molality of the solute

ΔT = Change in temperature

FREEZING POINT DEPRESSION

  • Solutions freeze at lower temperatures as compared to pure liquids. This phenomenon is used in "de-icing" schemes that employ salt, calcium chloride, or urea to melt the ice on streets and sidewalks and in the use of ethylene glycol as an "antifreeze" in car radiators.

  • The lowering in freezing point can be estimated by using:

                                 ΔT = i*Kf*m
    

where,

ΔT = Change in temperature

i = van 't Hoff factor

Kf = molal freezing point depression constant or cryoscopy constant

m = molality of the solute

CONCLUSION

  • Colligative qualities are those of a solution solely dependent on the concentration of solute molecules.
  • The four colligative properties are vapor pressure lowering, boiling point elevation, freezing point depression, and osmotic pressure.

FAQs:

1. What are the four colligative properties?

The four colligative properties are vapor pressure lowering, boiling point elevation, freezing point depression, and osmotic pressure.

2. Which are the Colligative properties?

Colligative characteristics are those of a solution determined only by the number of particles of the solute, such as ions or molecules, in a given quantity of the solvent rather than the type of the solute.

3. What are colligative properties? Give examples.

Compound attributes that are affected by the concentration of the substance present are known as colligative properties. The four primary colligative qualities are the boiling point, freezing point, vapor pressure, and osmotic pressureare the four primary colligative qualities.

We hope you enjoyed studying this lesson and learned something cool about Colligative Properties! Join our Discord community to get any questions you may have answered and to engage with other students just like you! Don't forget to download our app to experience our fun VR classrooms - we promise it makes studying much more fun! 😎

SOURCES

  1. Lumen Learning: https://courses.lumenlearning.com Accessed 26 Feb 2022
  2. Definition of Colligative Properties: https://www.thoughtco.com/definition-of-colligative-properties-604410 Accessed 26 Feb 2022
  3. Properties of Solutions: https://www.ck12.org/c/chemistry/freezing-point-depression/lesson/Properties-of-Solutions-MS-PS/?referrer=concept_details Accessed 26 Feb 2022