Solution and Colligative Properties

Chapter - Solution and colligative properties

 In normal life we rarely come across pure substances.
The utility or importance of mixture containing two or more pure substance in life depends on their composition. 

For Example 

• The properties of brass (mixture of Cu & Zn ) are quite different from those of German silver (mixture of Cu, Zn & Ni on Bronze ('mixture of Cu & Sn)
• 1 ppm of fluoride ions in water prevents tooth decay, while 1.5 ppm causes the tooth to become mottled & high concentration of fluoride ions can be poisonous ( for Example , NaF is used in rat poison)
• Binary solution : consisting of two components.

Type of solution
gaseous solution: solvent must be gas  -  Ex. mixture of oxygen and nitrogen gases, camphor in nitrogen gas
liquid solution: solvent must be liquid  - Ex. oxygen dissolved in water, Glucose dissolved in water
solid solution: Solvent must be solid Solution in Hydrogen in palladium, Amalgam of mercury with Sodium, copper dissolved in gold
Expressing Concentration of solution: Composition of a solution can be described by expressing its concentration. There are Several ways by which we can describe the concentration of solution quantitatively.
(1) Mass percentage (w/w) : -It is defined as the part of solute dissolved in 100 part of solution.
mass % = mass of the component x100 /Total mass of the solution
(2). Volume percentage (V/V) :- volume percentage of a component  

 =   volume of the component x 100 / Total volume of solution 

• Ex-10 % ethanol means 10 mL of ethanol is dissolved in 100 mL water, 
• a 35% ( v/v)Solution of ethylene glycol, an antifreeze, is used in cars for c oohing the engine that lowers the freezing point of water to 255.4K K (17.6℃)

(3). Mass by volume percentage(w/v):-measures the mass of weight of solute in grams vs. the volume of solutions in ml.
(4). Mole fraction (x) :
       mole fraction of a component = no. of moles of the components / total no. of moles of all the components      

                 X_A = n_A  / n_A+ n_B         X_B =     n_B  / n_A+ n_B
we know that  X_A+ X_B= 1
(5)molarity(M):- defined as the number of moles of solute dissolved in one litre (or one cubic diameter) of solution. molarity (M) = moles of solute/Volume of solution in litre
(6). Molality(m):- defined as the no of moles of solute dissolved in one Kg solvent.
                              =moles of solute / mass of solvent in Kg  
Note:-Molarity depends on temperature but molality does not. since molarity depends on volume which varies by temperature.
Solubility of a solid in a liquid : - Every solid does not dissolved in a given liquid. 

• It is observed that polar solutes dissolve in polar solvents & non polar solutes in won polar solvents. ex- NaCl and sugar 
• In general, a solute dissolves in solvent if the intermolecular interactions are similar in the two substances as solute & solvents or we may say like dissolve like .
• solubility depends on - the physical & chemical properties of the solute & solvent as well as on temperature  & presence of other chemicals.
• Effect of temperature on the solubility of solid in a liquid  is significantly affected. It must follow Le Chateliors principle. In general, the dissolution process is endothermic , the solubility should increase with rise in temperature & It is exothermic the solubility should decrease
• pressure does not have any significant effect on solubility of solid in. liquids. it is so because solid & liquids are highly incompressible & practically remain unaffected by changes in pressure.

Dissolution-is the dissolving process of the solid solute while crystallisation is the opposite ,causing the solid solute to remain undissolved.

Saturated solution	Unsaturated solution	Supersaturated solution
Can not dissolve any more quantity of solute in a given amount of solvent at given temperature	Can dissolve more quantity of solute at given temperature	Contains more of the dissolved solute than could be dissolved by solvent under normal circumstances

Solubility of a gas in a liquid: -Many gases dissolve in water . Oxygen dissolves only to a small extent in water. The dissolved oxygen sustain all aquatic life.
The solubility of gases in liquid depends upon-
a). nature of gas & liquid
b).Temperature: solubility of gas in liquid decreases with increase of  temperature. Since K. E. of gas is proportional to temperature. so its escaping tendency will increase with increase of temperature
c). pressure : solubility of gas in liquid increases with increase of pressure. It is so because gas and liquid are compressible.
Henry's law: - Henry was the first to give a quantitatively relation relation between pressure & solubility of a gas in a solvent which is known as Henry's law.
     It states that the solubility of a gas in a liquid is directly proportional to the  partial pressure of the gas present above the surface of liquid or solution at a constant temperature.
           Dalton , a contemporary of Henry , also concluded independently that the solubility of gas in a liquid solution is a function of partial pressure of the gas.
        The most Commonly used form of Henry's law states that " The partial pressure of the gas in vapour phase(p) is proportional to the mole fraction of the gas(x) in the solution". is expressed as:
              p_gas α  x                                      ………..  (1)
              p_gas =K_H x                     ………..  (2)

              here K_H = the Henry’s constant

                      p_gas = partial pressure of the gas

                       x = Mole fraction of the gas

note: solubility of gas decreases with increase of Henry's constant K_H at given pressure .

Applications of Henry's law in industry & some biological phenomena : -

• To increase solubility of CO₂   in soft drinks, beverage, soda water etc.  by applying high pressure and bottles are sealed under high pressure .
• To avoid bends , the tank used scuba divers are filled with air diluted with helium (11.7%helium,56.2 % nitrogen & 32.1 % oxygen) .
• At high altitudes , the partial pressure of oxygen is less . This leads to low concentrations of oxygen in the blood & tissues of people living at high attitudes or climbers. low blood oxygen causes climbers to become weak & unable to think clearly , symptoms of condition known as anoxia.

limitation of Henry's law :- Henry's law is applicable only if the fallowing condition are satisfied -

• • The pressure should be low & temperature should be high i.e. gas should behave a Ideal gas .
  • The gas should not undergo compound formation with solvent or association of dissociation in the solvent .

Next - Vapour pressure of liquid solution, ideal and non-solutions

Next- Azeotropes (constant boiling mixture)- and types

Next-Elevation of boiling point (Ebullioscopy)

Next-Depression of freezing point (cryoscopy)

Next- Osmosis and osmotic pressure

Click here to see more about SOLUTIONS- important questions with answer

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Solution and colligative properties (MCQ ,matching and reason assertion type question) with answer PART -1

solution and colligative properties (MCQ ,numerical type question)