Experiment- 1

Aim:

Determine the surface tension of a given liquid at room temp using

stalgmometer by drop number method

Requirements:

Stalgmometer, specific gravity bottle, a small rubber tube with a screw pinch

cork, distilled water, experimental liquid.

Theory:

In the drop number method, the number of drops formed by equal volumes

of two liquid is counted. If m1 and m2 is the mass of one drop of each of the

liquid having densities d1 and d2 respectively. If n1 and n2 is the number of

drops formed by volume v of the two liquids, then their surface tensions are

related as

¥1/¥2= (d1/d2)*(n2/n1)

One of the liquid is water its surface tension and density are known.Then te

surface tension of the given liquid can be calculated.

Procedure:

1. Clean the stalgmometer with chromic acid mix, wash with water and dry

it

2. Attach a small piece of rubber tube having a screw pinch cock at the

upper end of the stalgmometer.

3. Immerse the lower end of the stalgmometer in distilled water and suck the

water 1-2cm above mark A. adjust the pinch cork so that 10-15 drops fall per

minute

4.Clamp the stalgmometer allow the water drops to fall and start counting

the number of drops when the meniscus crosses the upper mark A and stop

counting when the meniscus passes mark B

5. Repeat the exercise to take three to four readings

6. Rinse the stalgmometer with alcohol and dry it

7. Suck the given liquid in the stalgmometer and count the drops as in case

of water

8. Take a clean dry weighing bottle weighs it with water as well as with

liquid.

9. Note the temp of water taken in a beaker.

Observations:

Room temp=t0C

Density of water=dw

Surface tension of water=¥ dynes/cm

No of drops From a Fixed Volume Mean

Liquid 1…. 2…… 3….. nl=

Water 1…. 2……. 3…… nw=

Weight of empty specific gravity bottle=w1gram

Weight of specific gravity bottle+water=w2 gram

Weight of empty sp.gravity bottle+liquid=w3gram

Weight of water= (w2-w1)gram

Weight of liquid= (w3-w1)gram

Calculations:

Density of the liquid

Dl= (w3-w1)/(w2 –w1) *dw

Surface tension of liquid=

¥l/¥w = (dl/dw)*(nw/nl)* ¥w

Result

The surface tension of liquid is ………dynes/cm.

Experiment-2

Aim- Determine the surface tension of a given liquid by means of

stalgmometer using drop weight method.

Requirements- Stalgmometer , wide mouthed weighing bottle , a small

rubber tube with screw pinch cork, distilled water, experimental liquid.

Theory-

The size of the drop of liquid forming on a capillary end depends upon the

surface tension of the liquid. The drop falls when the total surface 2πr¥ is

equal to its weight (w)

i.e. w= mg= 2πr¥

if two liquids having surface tension ¥1 and ¥2 are allowed to fall through

the same capillary then

w1/w2 = m1/m2 = ¥1/¥2

Procedure-

1. Clean the stalagmometer with chromic acid mixture , wash with water

then with alcohol and dry it.

2. Attach a small piece of rubber tube having a screw pinch cork at the

upper end of the stalgmometer.

3. Immerse the lower end of the stalgmometer in distilled water and suck

the water 1-2cm above the mark A. Adjust the pinch cork so that 10-

15 drops fall per minute.

4. Clamp the stalgmometer and allow 10 drops of water to fall into the

pre-weighed wide mouthed weighing bottle.

5. Weigh the weighing bottle along with 10 drops of water. Repeat the

experiment three to four times.

6. Rinse the stalgmometer with the given liquid, dry it. Fill it with the

experimental liquid and the repeat the above steps.

Observations-

Room temperature = toC\

Density of water = dw

Surface tension of water= ¥w

Weight of empty weighing bottle=w1g

Weight of weighing bottle+ 10 drops of water=w2 gram

Weight of bottle+ 10 drops of liquid=w3gram

Weight of water= (w2-w1)gram

Weight of liquid= (w3-w1)gram

Calculations-

¥l/¥w= (w3-w1)/(w2- w1)

Result-

The surface tension of the given liquid is …………………. Dynes/cm

EXPERIMENT 3

Aim: To determine the viscosity of a given unknown liquid with respect

to water, at laboratory temperature, by viscometer. Requirements: Ostwald viscometer, rubber tube with screw pinch cock, stand, beaker, unknown liquid, distilled water. specific gravity bottle

Theory: The force of friction which one part of the liquid offers to another

part of the liquid is called viscosity. For measuring the viscosity coefficient,

Ostwald viscometer method is used which is based on Poiseuille’s law.

According to this law, the rate of flow of liquid through a capillary tube

having viscosity coefficient, , can be expressed as

r 4tP

8vl where, v= vol. of liquid (in ml)

t= flow time (in sec.) through

capillary r= radius of the

capillary (in cm)

l= length of the capillary (in cm)

P= hydrostatic pressure (in dyne/sq.cm) = viscosity coefficient (in poise). Since, the hydrostatic pressure (the driving force) of the liquid is given by P

= dg h (where h is the height of the column and d is the density of the

liquid);

P t ; or, d g h t

If, 1 and 2 are the viscosity coefficients of the liquids under study, d1, d2

, are their densities and t1 and t2 are their times of flow of equal volume of

liquids through the same capillary respectively, then

1 d1 g h t1 and 2

d2 g h t2

Hence,

1

d1t1

2 d 2t2

Here, usually the viscosity of given liquid is measured with respect to water

whose viscosity is known very accurately at different temperatures. The SI

physical unit of viscosity is the pascal-second (Pa·s), (i.e., kg·m−1

·s−1

). This

means: if a fluid with a

viscosity of one Pa·s is placed between two plates, and one plate is pushed

sideways with a shear stress of one pascal, it moves a distance equal to the

thickness of the layer between the plates in one second. The cgs unit for the

same is the poise (P), (named after J. L. Marie Poiseuille). It is more

commonly expressed, as centipoise (cP). [1 cP = 0.001 Pa·s]. Water at 20

°C has a viscosity of 1.0020 cP.

Procedure: 1. Note the laboratory temperature. 2. Wash the specific gravity bottle with distilled water and dry. 3. Take the weight of the empty & filled (with distilled water) specific

gravity bottle (with stopper). Then, weigh the filled with specific gravity

bottle h unknown given liquid. Use the data for measuring the densities. 4. Clean and rinse the viscometer properly with distilled water. Fix the

viscometer vertically on the stand and filled with specific amount (say 20ml)

of mixture (every time take the same volume). 5. Time of flows were recorded for each solutions (water and the given

liquid). 6. Take 3 to 4 readings. Observations: 1. Laboratory temperature=….

C

2. Density measurement:

Weight of empty R.D.bottle (w1) =…g.

Weight of R.D.bottle with water (w2) =…g.

Weight of R.D. bottle with liquid (w3) =…g.

So, weight of water (ww) = (w2-w1) =…g.

Sl no. Flow times (sec)

t1 t2 t3 mean

1

2

3

4

Calculations: 1. Determination of the density of the liquid (dl):

Density of liquid

(dl) Density of water

(dw)

Density of liquid (dl )

wl

d w ww

= Weight of liquid

(wl) Weight of water (ww)

(Take density of water =1.0g/ml at

25

2. Determination of the viscosity of the liquid (l )

Viscosity of the

liquid,

tl dl

l

w

tw

d w

Result: The viscosity of the given liquid with respect to water at laboratory

temperature was found to be ……..cP.

______

Experiment-4 Aim- To verify Beer Lambert’s law for dichromate solution. Theory-The primary objective of this experiment is to determine the concentration of an unknown K2 Cr2 O7 solution. The K2 Cr2 O7 solution used in this experiment has a blue color, so Colorimeter users will be instructed to use the red LED. A higher concentration of the colored solution absorbs more light (and transmits less) than a solution of lower concentration.

You will prepare five of known concentration (standard solutions). Each solution is transferred to a small, rectangular cuvette that is placed into the Colorimeter or Spectrometer. The amount of light hat pene ra es the s lution and strikes the photocell is used to compute the absorbance of each solu on. When you graph absorbance vs. concentration for the standard solutions, a direct relationship should result. The direct relationship between absorbance and concentration for a solution is known s Beer’s law. You will determine the concentr tion of n unknown K2 Cr2 O7 solution by

measuring its absorbance. By locating the absorba nce of the unknown on

the vertical axis of the graph, the corresponding concentration can be found on the horizontal axis. The concentration of the unknown can a so be found using the slope of the Beer’s law curve.

REQUIREMENTS Colorimeter cuvette five 20 × 150 mm test tubes two 10 mL pipets or graduated cylinders two 100 mL beakers 0. 01M K2 Cr2 O7 solution distilled water test tube rack stirring rod tissues (preferably lint-free)

PROCEDURE 1. Obtain small volumes of 0. 01M K2 Cr2 O7 solution and distilled water in

separate beakers. 2. Label five clean, dry, test tubes 1–5. Use pipets to prepare five standard

solutions according to the chart below. Thoroughly mix each solution with a stirring rod. Clean and dry the stirring rod between uses.

Test 0.01M

K2 Cr2 O7 . Distilled H2O Concentration

Tube (mL) (mL) (M)

1 2 8 0.002

2 4 6 0.004

3 6 4 0.006

4 8 2 0.008

5 ~10 0 0.0100 4. Prepare a blank by filling a cuvette 3/4 full with distilled water. To correctly

use cuvettes, remember: Wipe the outside of each cuvette with a lint-free tissue. Handle cuvettes only by the top edge of the ribbed sides. Dislodge any bubbles by gently tapping the cuvette on a hard surface. Always position the cuvette so the light passes through the clear sides.

You are now ready to collect absorbance-concentration data for the five standard

solutions.

a. Using the solution in Test Tube 1, rinse the cuvette twice with ~1 mL amounts and then fill it 3/4 full. Wipe the outside with a tissue and place it in the device (Colorimeter or Spectrometer). Close the lid on the Colorimeter. b. When the absorbance readings stabilize, c. Discard the cuvette contents as directed. Using the solution in Test Tube 2, rinse and fill the cuvette 3/4 full. Wipe the outside and place the cuvette in the device (close the lid of the Colorimeter). When the absorbance readings stabilize,

d. Repeat the procedure for Test Tubes 3 and 4. Trial 5 is the original 0.01M K2 Cr2 O7 solution. Note: Do not test the unknown solution until Step 9. e. When you have finished testing the standard solutions f.

10. Determine the absorbance value of the unknown K2 Cr2 O7 solution.

a. Obtain about 5 mL of the unknown K2 Cr2 O7 in another clean, dry, test tube. Record the number of the unknown in your data table. b. Rinse the cuvette twice with the unknown solution and fill it about 3/4 full. Wipe the outside of the cuvette, place it into the device. (Close the lid of the Colorimeter.)

c. Read the absorbance value displayed in the meter. When the displayed absorbance value stabilizes, record its value as Trial 6 in your data table.

d. Select Interpolate from the Analyze menu. Find the absorbance value that is closest to the absorbance reading you obtained in Step c above. Determine the concentration of your unknown K2 Cr2 O7 solution and record the concentration in your data table.

e. Dispose of any of the remaining solutions as directed. DATA TABLE

Trial Concentration (mol/L) Absorbance

1 0.002

2 0.004

3 0.006

4 0.008

5 0.010

6

Unknown number ____