Chemistry Project Report on
“Effect of Impurities on the
Boiling Point and Freezing Point of A liquid”
I, ____________ student of ___________________ is doing
project report entitled “Effect of Impurities on the
Boiling Point and Freezing Point of A liquid” being submitted to
___________________is an original piece of work done by me.
Effect of Impurities on the
Boiling Point and Freezing Point of A liquid
Boiling Point and Freezing Point : Generally, on
cooling a liquid its temperature falls gradually till it starts freezing. At
this point the temperature remains constant till whole of the liquid changes
temperature at which a certain liquid freezes, is termed as its freezing
point." Freezing point of water is 00C or 273 K.
In the same manner,
on heating a liquid its temperature rises gradually till a stage comes when
the temperature does not rise further and the liquid starts boiling. The fixed
temperature at which a certain liquid boils is termed as the boiling point of
liquid. The boiling point of water is 1000C or 373 K.
In terms of vapour
pressure (pressure exerted by the vapours of solution) Boiling point of a
liquid is the temperature at which vapour pressure of the liquid becomes equal
to the atmospheric pressure.
Freezing point of a substance is the
temperature at which the solid and the liquid forms of substance have same
Effect of impurities on Boiling Point
When an impurity is
added its boiling point is elevated i.e. its boiling point is increased.
The elevation in
boiling point increases with increase in concentration of the solute because
on adding the solute vapour pressure of the solution becomes lower than pure
solvent. Thus the solution has to be heated more to make the vapour pressure
equal to atmospheric pressure. Thus the boiling point gets elevated.
For example boiling
point of water is 100oC under normal atmospheric pressure. If we
add sugar or salt to this water its vapour pressure becomes lower and boiling
Generally, when 1 mole of any non
electrolyte is dissolved in 1 litre of water the elevation of boiling point is
AIM :- To determine the effect
of impurities on the freezing point of water.
APPARATUS REQUIRED : - 500 ml
beaker, boiling tubes, 1100 thermometer with 0.10C calibration,
cork, iron stand, stirrer.
MATERIAL REQUIRED :- Glucose,
ice, water and KNO3.
1) Take three clean and dry
boiling tubes and label them as 1,2,3.
2) Take 20ml distilled water
in each boiling tube. Add 1g of glucose to boiling tube no.2 and 2g of glucose
to boiling tube no. 3. Shake till the glucose is dissolved.
3) Put a mixture of ice and
KNO3 in a beaker and fix test tube no. 1 in it and dip a stirrer.
Insert a thermometer in a bored cork and fix in a stand in such a way that its
bulb dips in water in the boiling tube.
4) Water is stirred in the
boiling tube and watch the temperature which is falling gradually. Note the
temperature when it remains constant and water starts freezing. This is the
freezing point of the pure water.
5) Take away boiling tube no.
1 from the beaker and replace it by the boiling tube no. 2. Repeat the
experiment and note the freezing point of glucose solution (it is 5% since 1g
is dissolved in 20ml water).
6) Now place boiling tube no.
3 in position and repeat the experiment to note its freezing point. (10%
1) Freezing point of water
decreases due to the presence of dissolved glucose.
2) Depression in the freezing point increases
as the quantity of dissolved glucose increase.
:- To determine the effect of impurities on the boiling point of water.
: - Three boiling tubes each fitted with cork with two holes, 1100 thermometer
with 0.10C calibration, sand bath, burner, iron stand.
:- Glucose, water.
1) Take three clean
and dry boiling tubes fitted with a cork with two holes (each) one for the
thermometer and other for a delivery tube.
2) Take 20ml
distilled water in each boiling tube. Add 1g of glucose to boiling tube no.2
and 2g of glucose to boiling tube no.3. Shake till the glucose is dissolved.
3) Fit boiling tube
no. 1 with a thermometer, keeping its bulb above the level of water. Fit it
with a delivery tube, fit it in an iron stand and start heating it on a sand
4) Heat and watch the
temperature which rises gradually and note it when becomes constant, i.e. when
water starts boiling. This is the boiling point of pure water.
5) Now fit the
boiling tube no. 2 in the above described manner and heat it. Note the boiling
point of 5% glucose solution.
6) Similarly, note the boiling point
of 10% glucose solution.
1) Boiling point of
water increases due to the presence of dissolved glucose.
2) Elevation in the boiling point
increases as the quantity of dissolved glucose increase.
Boiling Point &
Freeezing Point as Colligative Property :
In the expression of Boiling
Point i.e. D Tb = Kbm it is clear that the elevation in boiling point depends
on modality i.e. the number of moles of solute dissolved in 1000 g of the
solvent and not upon the nature of solute.
Hence a colligative property.
Same in case of freezing
Application of Depression in
Freezing Point :
The running of a car in sub zero whether even
when the radiator is full of water (which freezes below 273 K) has been
possible due to fact that depression in freezing point of water takes place
when appropriate amount of a suitable solute (usually ethylene glycol) called
antifreeze is dissolved in water.
Effect of impurities
on freezing point
When an impurity is added its
freezing point is lowered i.e. its freezing point decreases.
The depression in freezing
point increases with the increase in concentration of the solute because on
adding the solute the vapour pressure of solution becomes lower than that of
pure solvent. Since freezing point is the temperature at which vapour pressure
of liquid and solid phase are equal, therefore, for the solution, this will
occur at a lower-temperature.
For example freezing point of
water is OoC under normal atmospheric pressure. If we add sugar or
salt to this water its vapour pressure lowers and freezing point decreases.
Generally, when 1 mole of any non-electrolyte is dissolved in 1 litre of
water the depression in freezing point of water is 1.860C.
1) The impurities present in a
liquid pull its two fixed points away from each other i.e. the freezing point
is lowered while the boiling point is raised.
2) The depression in freezing point and the
elevation in boiling point increases with increase in the concentration of the
solute or impurity i.e. these are the colligative properties that depends only
on the no. of moles of the solute. They are independent of the nature of the
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