THE SOLUTIONS 

 UNIT 2:THE SOLUTIONS

1/A = solvent 2/B =solute

w= given mass m = molar mass

(random mass (its is always fixed/constant

decided to be taken for one mole of solute or solvent)

for experiment)

• METHODS OF EXPRESSING CONCENTRATION OF SOLUTIONS:

  a) mass percentage of A =wA/wA+wB*100

       mass percentage of B =wB/wA+wB*100

  b) volume percentage of A =vA/vA+vB*100

       volume percentage of B = vB/vA+vB*100

  c) molarity

  i) M =wB1000/MBVme = wB/MB*V2

  ii) M =nB/V

  iii) nB = M*V2 (for finiding number of moles if M and V is given )

  iv) M1V1 =M2V2 (for dilution)

  v) M = mass percentage *10*d/GMM

  vi) M3V3 =M1V1 +M2V2

  d) molality ( moles per kg)

       m = wB/MBMA(kg) = wB1000/MBwA (g)

  e) mole fractin (x)

     xa = na/na+nb xb = nb/na+nb

                           xa + xb = 1

    {{@@m = x2 * 1000/x1*molar mass of solvent@@{{

EFFECT OF PRESSURE ON SOLUBILITY OF GASES IN LIQUIDS :

HENRYS LAW :

At constant temperature , the quantity of gas absorbed by a given volume of solvent is proportional to pressure of gas over the solutions provided that the gas does not enter into chemical combinations with their solvent.

APPLICATIONS OF HENRYS LAW:

• Soft drinks ,soda water and other carbonated beverages contains dissolved carbondioxide
• Anoxia
• Bends

 In underwater diving:

Henrys lw has important consequences in SCUBA diving.

SCUBA tanks are filled with compressed purified air. This air contains about

                       21% of OXYGEN

                       78% of NITROGEN

                        01% of HELIUM

and if a diver rises to the surface at the right rate , the N2 can slowly and safely leave the body through the lungs. but if the diver rises too quickly, the N2 forms bubbles in the body . This can cause tissue and nerve damage. This condition is know as BENDS. To avoid this, divers uses oygen diluted with helium

HENRYS LAWW CONSTANTS (gases in water at 298.15k)

NITROGEN(N2) 1600

OXYGEN(O2) 770

HELIUM(He) 2700

HENRYS LAW:

P =Kh xB

for numericals

a) xB = P/KH (units should be same)

b) nB =P/KH *55.5 (for 1 liter of water)

           ( answer will be in mol/lit)

c) since nB = wB/mB so wB =nB*mB

                     =P/KH*55.5MB (answer will be in g/l)*

d)P1/m1 = P2/m2

RAOULTS LAW :

a)For solutions containing non-volatile solute

PA = PA xA

b) For solutions containing volatile solutions + volatile solvent

PT =PA xA +PB xB

P = (PA - PB)*A +PB

IDEAL SOLUTIONS

a) obey raoults law

b) /\ Hmix = 0

c) /\ Vmix = 0

d)/\ Smix = 0

e)/\ Gmix = 0

COLLIGATIVE PROPERTIES :

RELATIVE LOWERING OF VAPOUR PRESSURE

i) /\ P/PA =xB

ii) MB = wB*MA/wA (PA/ /\P)

ELEVATION IN BOILING POINT :

The boiling point of a liquid may be defined as the temperature at which its vapour pressure becomes equal to atmospheric pressure

/\TB is directly propotional to /\P

/\ TB is directly propotional to xB

/\TB =KxB =K wB*mA/mB*wA

$/\ TB = Kbm$

MB =wB Kb/wB /\Tb Kb = constant

                                                            /\Tb = collogative propertie

DEPRESSION IN FREEZING POINT :

i) In freezing point of substance in the temperature of which the solid and iquid phase of substance have the same vapour pressure

ii) or it may also be defined as the temperature at which a particular solution is in equilibrium with solid solvent

iii) The freezing point of any pure liquid is fixed

/\Tf is directly propotional to /\P

DEPRESSION IN FREEZING POINT:

i)/\ Tf =mKf

ii) MB =Kf*wB*1000/wA*/\Tf

TYPES OF SOLUTIONS :

i) Isotonic solution 2 solution having same osmotic pressure

pi1 =pi2 (at same temp)

ii) hyper tonic 1st if pi1 is greater than pi2 solution is hyper tonic w.r.t 2nd soltion

iii) hypo tonic 2nd solution hypo tonic w.r.t 1st solution

OSMOTIC PRESSURE:

i) pi =CRT

ii) mB =wB*RT/PI V

iii) pi 1/C1 = pi 2/C2

APPLICATIONS OF OSMOSIS :

i) improving throat condition through gargels

ii) pickles preservation

iii) absorption of water by plants

iv)shirveling of raw mangoes to pickels

v)dehydration of body by drinking sea water

AZEOTROPES:

many binary solutions at definate compositions behave like pure liquides because their vapours have the same composition of the components as in solutions . Azeotropes are defined as the mixture of liquids which boil at constant temperature like pure liquid and posses some compositions of components in liquid as well as in vapour phase.

RELATION OF O.P WITH C.P:

i) pi =/\P/PA * dRT/mB

ii)pi = /\ Tb * dRT/1000*Kb

iii)pi = /\ Tf * dRT/1000*Kf