Students Assignment about solutions

1.Importance of phenomenon of solubility in pharmacy

2.Solubility of Liquid in Liquid

3.Solubility of Gas in Liquid

4.Solubility of Solid in Liquid

5.Colligative Properties of solutions and its application in Pharmacy

6.Electrolytes, Activity and Activity Coefficient

Colligative Properties of Electrolytes

  Since these properties depend on the number of particles dissolved, solutions of electrolytes (which dissociate in solution) should show greater changes than those of nonelectrolytes.

  However, a 1 M solution of NaCl does not show twice the change in freezing point that a 1 M solution of methanol does.

Diffusion

•Movement of molecules and ions from an area of higher concentration to an area of lower concentration

Osmosis in Cells

•If the solute concentration outside the cell is less than that inside the cell, the solution is hypotonic.

•

•Water will flow into the cell, and hemolysis results.

(a) A cell placed in an isotonic solution. The net movement of water in and out of the cell is zero because the concentration of solutes inside and outside the cell is the same.

Osmosis

•Movement of fluid from and area of lower solute concentration to an area of higher solute concentration

•Some substances form semipermeable membranes, allowing some smaller particles to pass through, but blocking other larger particles.

Colligative Properties

  Colligative Properties

1.  Boiling Point Elevation – The increase in boiling point of a solution relative to that of the pure solvent is directly proportional to the number of solute particles per mole of solvent molecules.  That is,

  DTb = i Kb m

where DTb = increase in boiling point relative to that of the pure solvent, Kb is called the molal boiling point elevation constant, and m = molality of the solution.

2.  Freezing Point Depression – Like the boiling point elevation, the decrease in freezing point of a solution relative to that of the pure solvent is directly proportional to the molality of the solute.  That is,                                    DTf = iKf  m

where DTf  = decrease in freezing point relative to that of the pure solvent, Kf is called the molal freezing point depression constant, and m = molality of the solution.

Boiling Point Elevation and Freezing Point Depression

  Nonvolatile solute-solvent interactions also cause solutions to have higher boiling points and lower freezing points than the pure solvent.

•Raises (elevates) the boiling point

•Definition - the temperature at which the vapor pressure of a liquid equals the atmospheric pressure

•More solute increases the temperature at which the vapor pressure equals the atmospheric pressure

•Directly proportional to solute concentration.

DTb = (Tb -Tb°) = i ·m ·kb

  Where, DTb = BP. Elevation 

  Tb = BP of solvent in solution

  Tb° = BP of pure solvent

   m = molality ,     kb = BP Constant

 

   

Raoult’s Law

PA = XAP°A

  where

•XA is the mole fraction of compound A

•P°A is the normal vapor pressure of A at that temperature

–

NOTE:  This is one of those times when you want to make sure you have the vapor pressure of the solvent.

•The lowering of the vapour pressure when a non-volatile solute is dissolved in a volatile solvent (A) can be described by Raoult’s Law:

•

  PA = cAP°A

PA = vapour pressure of solvent A above the solution

cA = mole fraction of the solvent A in the solution

P°A = vapour pressure of pure solvent A

Vapor Pressure

  Because of solute-solvent intermolecular attraction, higher concentrations of nonvolatile solutes make it harder for solvent to escape to the vapor phase.

  Therefore, the vapor pressure of a solution is lower than that of the pure solvent.

•Result of the escape of solvent molecules from the liquid to the gas phase

•Increases the amount (partial pressure) of the gas phase solvent molecules above the liquid

•If a closed system will reach equilibrium vapor pressure

Colligative Properties of solutions

Colligative properties depend on the number of particles rather than their nature

• Lowering of the vapor pressure (Raoult’s law)

• Elevation of the boiling point (“ebulioscopy”)

• Depression of the freezing point (“cryoscopy”)

• Osmotic pressure

•

•Changes in colligative properties depend only on the number of solute particles present, not on the identity of the solute particles.

•Among colligative properties are

ØVapor pressure lowering

ØBoiling point elevation

ØMelting point depression

ØOsmotic pressure