Solutions 4 Flashcards
what are colligative properties
All these properties depend on the number of solute
particles irrespective of their nature relative to the total number
of particles present in the solution. Such properties are called
colligative properties
These are: (1) relative lowering of vapour
pressure of the solvent (2) depression of freezing point of the solvent
(3) elevation of boiling point of the solvent and (4) osmotic pressure of
the solution.
when does a liquid boil
the vapour pressure of a
liquid increases with increase of temperature. It boils at the
temperature at which its vapour pressure is equal to the atmospheric
pressure. For example, water boils at 373.15 K (100° C) because at
this temperature the vapour pressure of water is 1.013 bar (1
atmosphere).
what is the boiling point of the solution wrt to solute
The vapour pressure increases with temperature.
When a non volatile solute is added to a solvent to make a solution, its vapour pressure decreases.
IN order to make the solution boil, its temperature has to be raised to equal the vapour pressure to 1atm
so the boiling point of the solution is always greater than the solvent
for dilute
solutions the elevation of boiling point (∆Tb
) is
directly proportional to the molal concentration of
the solute in a solution.
what is Kb
Kb
is called Boiling Point
Elevation Constant or Molal Elevation Constant (Ebullioscopic
Constant). The unit of Kb
is K kg mol-1
It is the elevation in boiling point of a solution of unit molality.
when does a liquid freeze
The lowering of vapour pressure of a solution causes a lowering of the
freezing point compared to that of the pure solvent
the freezing point of a substance may be defined
as the temperature at which the vapour pressure
of the substance in its liquid phase is equal to its
vapour pressure in the solid phase. A solution
will freeze when its vapour pressure equals the
vapour pressure of the pure solid solvent
what is kf
The proportionality constant, Kf
, which depends on the nature of the
solvent is known as Freezing Point Depression Constant or Molal Depression Constant or Cryoscopic Constant. The unit of Kf
is K kg
mol-1
what are semipermeable membranes
Semipermeable membranes are those membranes which allow the passage of only certain molecules through it.
These membranes appear to
be continuous sheets or
films, yet they contain a
network of submicroscopic
holes or pores.
Small solvent molecules can pass through these but larger solute molecules cannot.
These membranes can be of
animal or vegetable origin
and these occur naturally
such as pig’s bladder or
parchment or can be
synthetic such as cellophane, cellulose acetate.
what is osmosis
The movement of solvent molecules from pure solvent to solution across a semi permeable membrane is called osmosis.
mvmnt of solvent molecules from a region of low conc of solution to high conc of solution
solvent molecules
always flow from lower concentration to higher concentration of solution.
what is osmotic pressure
it is the excess pressure that is applied to a solution in order to prevent osmosis or to prevent the entry of solvent molecules into it.
capital pi= CRT
C- concentration of soln in mol/L
R- 0.0821 Latm/mol K
T- absolute temp
Osmotic pressure is a
colligative property as it depends on the number
of solute molecules and not on their identity.
For dilute solutions, it has been found
experimentally that osmotic pressure is
proportional to the molarity, C of the
solution at a given temperature T.
outline thr advantages of osmotic pressure to other colligative properties
i)The osmotic pressure method has the advantage over
other methods as pressure measurement is around the room
temperature and the molarity of the solution is used instead of molality.
ii)As compared to other colligative properties, its magnitude is large
even for very dilute solutions. (of the order of 10^-3 atm)
ii)iThe technique of osmotic pressure for
determination of molar mass of solutes is particularly useful for
biomolecules( proteins, polymers other macromolecules) as they are generally not stable at higher temperatures
and polymers have poor solubility.
what is the limitation of osmotic pressure method
It has experimental difficulties
what is isotonic solutions
Two solutions having same osmotic pressure at a given
temperature are called isotonic solutions. When such solutions
are separated by semipermeable membrane no osmosis occurs
between them.
As osmotic pressures are qual, at the same temperature, the concentration will be equal.
give a real life example of isotonic solt=utions
m. For example, the osmotic pressure associated with
the fluid inside the blood cell is equivalent to that of 0.9% (mass/
volume) sodium chloride solution, called normal saline solution and
it is safe to inject intravenously. On the other hand, if we place the
cells in a solution containing more than 0.9% (mass/volume) sodium
chloride, water will flow out of the cells and they would shrink. Such
a solution is called hypertonic. If the salt concentration is less than
0.9% (mass/volume), the solution is said to be hypotonic. In this
case, water will flow into the cells if placed in this solution and they
would swell.
what are hyper/hypotonic solns
Hypotonic solution refers to a solution containing a lower amount of solute in comparison to the solute concentration in other solutions, across a semipermeable membrane.
gr
i)pickled mango
ii) wilted flowers
iii)shrivelled carrots
iv)mvmnt of water in plants
v)candied fruit
A raw mango placed in concentrated
salt solution loses water via osmosis and shrivel into pickle. Wilted
flowers revive when placed in fresh water. A carrot that has become
limp because of water loss into the atmosphere can be placed into the
water making it firm once again. Water will move into them through
osmosis.
Water movement from soil into
plant roots and subsequently into upper portion of the plant is partly
due to osmosis. The preservation of meat by salting and of fruits by
adding sugar protects against bacterial action. Through the process
of osmosis, a bacterium on salted meat or candid fruit loses water,
shrivels and dies.
what is edema
People taking a lot of salt or salty food experience water retention in
tissue cells and intercellular spaces because of osmosis. The resulting puffiness or swelling is called edema.
what is reverse osmosis
The direction of osmosis can be reversed if a pressure larger than the
osmotic pressure is applied to the solution side. That is, now the
pure solvent flows out of the solution through the semi permeable
membrane. This phenomenon is called reverse osmosis.
what is desalination of sea water
When pressure more than osmotic pressure is
applied, pure water is squeezed out of the sea
water through the membrane. A variety of
polymer membranes are available for this
purpose.
The pressure required for the reverse osmosis
is quite high. A workable porous membrane is a
film of cellulose acetate placed over a suitable
support. Cellulose acetate is permeable to water
but impermeable to impurities and ions present
in sea water. These days many countries use
desalination plants to meet their potable water
requirements.
what happens when ethanoic acid is placed in benzene
Molecules of ethanoic acid (acetic acid) dimerise in
benzene due to hydrogen bonding. This normally happens
in solvents of low dielectric constant. In this case the number
of particles is reduced due to dimerisation.
In this case, the molar mass will be odubled
what happens when kcl is put in water
KCL dissociated into K+ and Cl- ions so the Tf will be shown for twice the no of particles
Hence the molar mass will be halved
abnormal molar mass
a molar mass
that is either lower or higher than the expected or normal value is called
as abnormal molar mass.
In 1880 van’t Hoff introduced a factor i, known as the van’t Hoff
factor, to account for the extent of dissociation or association.
In
case of association, value of i is less than unity while for dissociation it
is greater than unity.
define vant hoff factor
it is the ratio of observed or experimental value of collimation property to the calculated/theoretical value of the colligative property. It is used to represent the extent of association or dissociation in a solution.
