Determination of surface tension of given liquid by drop count method
Aim
To determine
the surface tension of a given liquid by drop count method.
Requirement
- Stalagmometer
- 100ml beaker
- Burette stand
- Distilled water.
Principle
The surface
tension is defined as force in dynes acting along the surface of the liquid at
right angle to any line in 1 cm length. In CGS system the unit is dynes/cm
(dynes cm-1). In SI system the unit is newton/ meter (Nm-1).
The surface tension of a liquid can be determine by using stalagmometer by drop count method. The surface tension of a liquid sample is calculated by following formula.
γ2= n1ρ2/n2ρ1 × γ1
Where,
γ2 =
Surface tension of a given liquid sample in dynes/cm
γ1 = Surface tension of a given liquid water is 72.75 dynes/cm
n2 =
Number of drops of liquid sample
n1 =
Number of drops of water
ρ2 =
Density if liquid sample in g/ml
ρ1
= Density of water ( 0.9998 g/ml)
The surface tension is determined by using stalagmometer. The density of water and density of liquid sample can be determined by using specific gravity bottle.
Procedure
1. Take a clean
stalagmometer and rinse with acetone then dry it in a hot air oven.
2. Fix the
stalagmometer to the stand firmly in a hot vertical position and tipped the
stalagmometer in a beaker of water and suck water to flow down and stop the
counting of drops after the water meniscus passes from upper mark to lower
mark.
3. If the
number of drops in between the 15 – 20 drops
per minute, go to repeat in the stop mentioned above when the water pass the
lower mark, stop the counting and note the number of drops of water.
4. Remove the
water drops, clean the stalagmometer then repeat the procedure for counting the
drops of sample by following the above mentioned procedure surface tension of
the given sample was found to be
γ2= n1ρ2/n2ρ1 × γ1
Note : Density of water is 0.9998 g/ml
Surface tension of water is 72.75
dynes/cm
Calculations:
i ) Determination of Density of given liquid sample
Room
temperature = ---------- °C
Weight of
empty specific gravity bottle (W1) = -------------------g
Weight
of specific gravity bottle and
water (W2) = -------------------g
Weight of
specific gravity bottle and liquid sample
(W3) = -------------------g
Mass/
weight of Water = W2 – W1
= -------------------------
= ------------------------- g
Mass/ weight
of liquid sample = W3 – W1
= -------------------------
= ------------------------- g
Density of liquid sample = Mass of
liquid sample / Mass of water ×Density of water
= ---------------------------
= --------------------------
= -------------------------- g/ml
ii ) Determination of Surface tension of given liquid sample
S.No |
Number of drops of water(n1) |
Number of drops of sample (n2) |
|
1 |
|
|
|
2 |
|
|
|
3 |
|
|
Average |
|
|
Surface tension of a given liquid sample (γ2)
= --------------------- ?
Surface tension of a given liquid water (γ1) = 72.75 dynes/cm
Number of
drops of liquid sample (n2) = ----------------------- drops
Number of
drops of water (n1) = ------------------------
drops
Density if
liquid sample (ρ2) = ------------------------ g/ml
Density of
water (ρ1) = ------------------------- g/ml
Surface tension of a given liquid sample γ2= n1ρ2/n2ρ1 × γ1
=
-------------------------------
=
-------------------------------
= ------------------------------- dynes / cm
Report
The surface
tension of the given liquid sample by drop count method was found to be ----------------------- dynes/cm.
){kind=link}
0 Comments