FACULTY OF APPLIED SCIENCES
LABORATORY REPORT
PHYSICAL CHEMISTRY (CHM 431) Title of Experiment
Properties Of Colloidal Dispersion
No. Experiment
7
Name of student
Ernie Najwa Najihah Binti Faidi
Student ID number
2017283562
Programme code
AS246
Partner’s name
Syeril Nurfatihah Binti Suhaimi
Date of experiment is done
6th May 2018
Date of lab report is submitted
27th May 2018
Lecturer’s name
Dr. Noraini Binti Hamzah
Instructor’s
name
Erma Hafiza
INTRODUCTION A colloid is a dispersion of particles of one substance throughout a dispersion medium made of another substance. The distributed substance is the disperse phase and the continuous substance is the dispersion medium. In colloidal solution, particles are dispersed or spread throughout the dispersion such as water. The size of colloid particles is intermediate between the coarse suspension and ordinary solution. Therefore, colloids are somewhere between a homogeneous solution and heterogeneous mixture. Random collisions keep them dispersed throughout the dispersion medium due to the small particle size and neither sinks to the bottom nor dissolves the solvent. The course particle suspension can be seen under a microscope and will settle under the action of gravity while the colloidal solution particle are not visible under microscope but instead, can be detected under an electron microscope. These particles of a colloidal solution may be very large single molecules or aggregates of small molecules, atom or ions.
OBJECTIVES 1. To study the general properties of a ferric hydroxide sol, starch solution and some true solutions.
APPARATUS 1. Beaker or conical flask (1dm3) 2. Test tube 3. Boiling tube 4. Teat pipette 5. Filter funnel and filter paper 6. Cellophane membrane 7. Hot water bath
CHEMICALS 1. Ferric hydroxide sol, Fe(O)3 2. Deionised water 3. 5% starch solution 4. 1% starch solution 5. 10% sucrose solution 6. 0.1M Sodium chloride solution, NaCl
7. Dilute iodine solution 8. 0.1M Silver nitrate solution, AgNO 3 9. 0.1M Sodium phosphate solution, Na 3PO4 10. 0.1M Sodium sulphate solution,Na 2SO4 11. Potassium chromate solution, K 2CrO4 12. Fehling solution 13. Dilute sulphuric acid, H2SO4 14. Potassium hexacyanoferrate (II) trihydrate, K 4Fe(CN)6.3H2O or Potassium hexacyanoferrate (III), K 3Fe(CN)6 or Potassium thiocyanate, KSCN.
PROCEDURE A. Dialysis
Five dry test tubes was cleaned and filled with 5cm3 each of the following solutions: Test tube A: 5% starch solution Test tube B: sodium chloride solution 0.1M Test tube C: Ferric hydroxide solution Test tube D: 10% sugar solution Test tube E: potassium chromate solution
The mouth of the test tubes was wrapped with pre – soaked cellophane membrane and fasten it tightly with a thread. It was then dipped in different small beakers containing deionised water and was clamped and leaved for one hour. The water level in the beaker was make sure is always lower9 than the level of the solutions in the test tubes. After one hour of dialysis, 3cm3 of the deionised water in each beakers was took and tested with a few drops of the following rea gents:
Starch solution : dilute iodine solution Chloride solution: silver nitrate solution Fe3+ ions solution: potassium hexacyanoferrate (II) trihydrate solution Sugar solution: Fehling solution (the mixture was warmed to about
60ºC in the water bath)
Chromate ion solution: ethanol solution (4 – 6 drops of dilute H2SO4
was added to the mixture and was then warmed in water bath at a temperature above 80ºC)
The observations was then recorded.
B. Stability Of Ferric Hydroxide Sol
Three test tube was cleaned and dried and was then filled with 2cm3 of ferric hydroxide sol, labelled as test tube 1,2 and 3. 2cm3 of an electrolyte was next added to each of the test tubes according to the table below: Test Tube
Type Of Electrolyte Added
1
Sodium Chloride, NaCl
2
Sodium Sulphate, Naso4
3
Sodium Phosphate, Na3PO4
The test tubes was then shook well after the addition of the electrolyte and was left to stand for a few minutes. The observation was then recorded.
C. Tyndall Effect
Five 100cm3 beakers was cleaned and dried, labelled as A, B, C, D and E. each beaker was then filled about ½ full with the following solutions:
Beaker A: 1% starch solution Beaker B: 5% starch solution Beaker C: ferric hydroxide solution Beaker D: 10% sugar solution Beaker E: potassium chromate solution
The Tyndall Effect of each of the solution was observed by using a narrow beam of light from a laser pointer and the observation was then recorded.
RESULTS A. Dialysis
Test Tube
Observation
A
No reaction
B
Colourless to cloudy
C
Blue black solution formed
D
Light blue to brick rich solution
E
Yellow to green solution
B. Stability Of Ferric Hydroxide Sol
Test Tube
Observation
1
No precipitate form
2
Precipitated formed
3
More precipitate formed (chalky)
C. Tyndall Effect
Beaker
Observation
A
Light less scattered
B
Light more scattered
C
Light slightly scattered
D
Light not scattered
E
Light not scattered
DISCUSSION Colloid dispersions exhibit several properties. Among these are the scattering of a light beam directed through a colloidal dispersion. This is known as the Tyndall effect and its magnitude is due to the size and number of particles present. When observed under ambient light, colloidal dispersions may appear translucent, opalescent or cloudy depending on the type of colloid and the degree of particle concentration and dispersion. The Tyndall effect is due to the scattering of light by colloidal particles. Since the dimensions of colloidal particles are comparable to the wavelength of ultraviolet and visible radiations, they scatter these and get illuminated. Tyndall effect may be defined as the scattering of light by colloidal particles
present in a colloidal solution. Tyndall effect is not exhibited by true solutions. This is because the ions or molecules present in a true solution are too small to scatter light. Thus, Tyndall effect can be used to distinguish a colloidal solution from a true solution. Tyndall effect also establishes the fact that colloidal systems are heterogeneous in nature. Next, dialysis is the process of separating the electrolytes in the colloidal state from those present in the true solution by means of diffusion through a semi-permeable membrane that is based on the fact that colloidal particles are retained by a semi - permeable membrane while the ions of the electrolyte pass through it. In the stability of sol experiment, the coagulation was shown where it is the irreversible collapse of the colloidal particles into bulk phase and settles as precipitate. Besides that, lyophilic sols are more stable and show greater resistance to coagulation than lyophobic sols because most of lyophilic sols are neutral. Lyophobic sols are stable due to repulsion between similarly changed particles. If this charge is removed by adding electrolytes, coagulation occurs. The particles come together to form larger masses, which settles under the action of gravity.
CONCLUSION To conclude, from this experiment, the general properties of a ferric hydroxide solution, starch solution as well as some true solution was determined and identified. The objectives of this experiment was successfully achieved.
QUESTIONS
1. With an appropriate example, explain the difference between true solution, suspension and colloid.
True Solution is a homogeneous mixture of two or more substances in which substance dissolved in solvent has the particle s ize of less than 10-9 m or 1 nm. Simple solution of sugar in water is an example of true solution. Particles of true solution cannot be filtered through filter paper and are not visible to naked eye. Suspension is a heterogeneous mixture in which particle size of one or more components is greater than 1000nm. Contrary to True solution, particles o f suspension are big enough to be seen with naked eye. Mud is an example of a s uspension. Colloidal is a heterogeneous mixture in which particle size of substance is intermediate of true solution and suspension between 1-1000 nm. Smoke from a fire is
example of colloidal system in which tiny particles of solid float in air. Just like true solutions, colloidal particles are small enough and cannot be seen through naked eyes.
2. What are gels and their types? For different type of gels explain their differences on dehydration and soaking properties.
Types of gel and their differences in term of dehydration and soaking properties. Elastic gel possessed elasticity properties. For its dehydration properties, the elastic gel turns to solid mass on dehydration which can again be converted into gel b y addition of water followed by heating and cooling. The second type of gel is non – elastic gel that turns to solid mass on dehydration but the solid mass cannot be converted again into gel after addition of water followed by heating and cooling. In soaking properties, the gel will absorbed water and swell when soaked into water while the water is not absorbed by the non – elastic gel and the size remains when soaked into water.
3. What kind of information can be obtained from light – scattering experiment on colloidal particles, in aqueous solutions? Explain your answer.
When light passes through a medium that contain no particles larger than about 10-9 m in diameter, the path of the light cannot be detected and the medium is said to be optically clear. When, colloidal particle is present, some of the light is scattered and the incident beam passed through weakened intensity. The scattering is called Tyndall effect. While, the path of the light through the medium, made visible as a result of scattering known as Tyndall beam. Analysis of the scattering as a function of the angles provides valuable information about the sizes and shapes of colloidal particles. When these are singles macromolecules, the technique is therefore useful in determining molar mass.
REFERENCE 1. Aniruddha R., (2010), Surface and Colloid Chemistry Principles and Applications, Retrieved from December 10, 2014 from https://www.scribd.com/doc/55436426/Surface-andColloid-ChemistryPrinciples-and-Applications
2. https://shankerdayal.wordpress.com/2014/07/14/difference-between-true-solutionsuspension-and-colloidal-solution/
