CHM 431 PHYSICAL CHEMISTRY
TITLE
: COLLOIDS CHEMISTRY
NAME
: NURFADHILAH BINTI JAAFAR
ID NUMBER
: 2016675256 2016675256
GROUP
: AS 246 3B
SUBMITION DATE
: 14
LECTURER’S NAME
: MADAM ZARILA MOHD SHARIFF
TH
NOVEMBER 2016
TITLE Colloids Chemistry OBJECTIVES a) To study the general properties of a ferric hydroxide sol, starch solution and some true solutions INTRODUCTION A colloid is a type of mixture and was first introduced by Thomas Graham (1861) which consists of dispersion phase and dispersion medium. There are 8 classes of colloidal system which are made up of solids, gases and liquid. The table shown below summarize the different type of colloids.
Sols are classified can be classified into two types which are lyophilic (liquid loving) and lyophobic (liquid hating). The particle size of the dispersed phase typically ranges from 1nm to 1000 micrometer because of the ability to pass through the filter paper but cannot pass through the animal or vegetable membrane. On the other hand the particles of colloids are smaller than the particles represents in the suspension. However, cellophane membrane, restrict the passage of dispersed colloidal particles more than they restricted the passage of dispersed of dissolved ions or molecules. Colloids exhibit physical properties such as Tyndall effect, electrical effect, and molecular collision effects which depend on the types of colloid experimented.
When the concentrated iron (III) chloride solution is heated, it will undergoes hydrolysis and gives off heat in exothermic reaction with the production of gas. The dark brown precipitate of insoluble iron (III) hydroxide forms. The hydrolysis process is reversible FeCl3(aq) +3H2O(l)
Fe(OH)3 (s) + 3HCl(aq)
After that, iron (III) chloride was added to the beaker of hot water, then a colloidal iron(III) oxide was formed with brown red in colour.
PROCEDURE A. Dialysis 1. 5 test tubes were cleaned and dried and filled with 5cm 3 with each of the following solutions: Test tube A: 5% starch solution Test tube B: sodium chloride solution 0.1M Test tube C: ferric hydroxide sol Test tube D: 10% sugar solution Test tube E: potassium chromate solution (K 2CrO4) 2. The mouths of all the test tubes were wrapped with pre-soak cellophane membrane and were fastening tightly with a thread. (Note: The cellophane membrane must be soaked in deionised water at least 24 hour prior to your experiment). 3. The test tubes were inverted and dipped in different small beakers containing deionised water. The test tubes were clamped and left for 1 hour. The water level in the beakers was always made sure were lower than the level of the solutions in test tubes. 4. 3 cm3 of the deionised water was taken from each beakers after 1 hour dialysis and were tested with a few drops of the following reagents: Starch solution: dilute iodine solution Chloride solution: silver nitrate solution Fe3+ ions solution: potassium hexacyanoferum (II) solution Sugar solution: Fehling solution (warm the mixture to about 60 oC in the water bath) Chromate ion solution: ethanol solution (add 4-6 drops of dilute H 2SO4 to the mixture in the water bath)
5. All the observations are recorded in the data sheet.
B. Stability of ferric hydroxide sol 1. 3 test tubes were cleaned and dried 2. All the test tubes were filled with 2 cm 3 of ferric hydroxide sol and was labelled as test tubes 1,2 and 3. 3. 2 cm 3 of an electrolyte were added to each of the test tube according to the table below: Test tube no
Type of electrolyte added
1
Sodium chloride, NaCl
2
Sodium sulphate, Na 2SO4
3
Sodium phosphate, Na 3PO4
4. The test tubes were shaken and left to stand for a few minutes. The observations were recorded in the data sheet.
C. Tyndall effect 1. 100 cm 3 beakers were cleaned and the beakers are labelled as A,B,C,D and E. 2. Each beaker was filled with about ½ full with the following solutions: Beaker A: 1% starch solution Beaker B: 5% starch solution Beaker C: ferric hydroxide sol Beaker D: 10% sugar solution Beaker E: potassium chromate solution (K 2CrO4) 3. The Tyndall effect was observed of each solution by using a narrow beam of light from a laser pointer. The observation was recorded. CHEMICALS 5% and 1% of Starch solution, Ferric hydroxide sol, 10% sucrose solution, potassium chromate solution, 0.1 M sodium chloride solution, 0.1 M sodium sulphate solution , 0.1 M sodium phosphate solution, iodine solution, silver nitrate solution, potassium hexacyanoferum (II) solution, Fehling solution, dilute sulphuric acid, deionised water
DISCUSSIONS
Colloid appears homogenous like solution, but they consist of comparatively large particles of one substance dispersed throughout the dispersion medium. In the first part of experiment we observed the dialysis of deionised water with a few solutions labelled as test tube A,B,C, D, E. In test tube A contain starch solution it change from colourless and change light brown. This is because; the starch solution cannot pass through the cellophane membrane due to its large particle, hence left with the remaining light brown iodine solution. Deionised water from Sodium chloride solution in test tube B was tested with silver nitrate solution change from colourless to cloudy solution with the presence of white precipitate. On the other hand, test tube C with ferric hydroxide sol changes the colourless deionized water to emerald green. Sugar solutions in the test tube D change from colourless to light blue with brick red precipitates. Also, potassium chromate solution in test tube E gives changes from bright yellow to dull light yellow. Both solution in test tube D and E gives changes to the small particles of the solutions. So when they are being soak in deionized water, it pass through the membrane thus, gives reaction and colour changes.
The second part of the experiment involves the stability of ferric hydroxide sol which was added to 3 test tubes. Test tube 1 was added with sodium chloride and it change from dark brown to clear light brown solution. When added sodium sulphate to Test tube 2 it give colour changes of dark brown ferric hydroxide sol to 2 layer of solution consists of clear light orange solution on the top and orange deposits at the bottom layer. Next, sodium phosphate was added to test tube 3 and change from brown to cloudy creamy orange solution. The deposits or precipitate of varying quantities were formed on each test tube. These are the reactions involved in each test tube:
Fe(OH)3+ 3NaCl ----> Fe(Cl)3+ 3NaOH 2Fe(OH)3+ 3Na2SO4 ----> Fe2(SO4)3+ 6NaOH Fe(OH) 3+ Na3PO4 ----> Fe(PO4) + 3NaOH
The charges of the ions that will attach the Fe will contribute to the quantity of the precipitate formed. Among the electrolytes, PO 4 is the most electronegative among the others and it yielded the most prominent precipitates. SO 4 comes next while Cl - has the least amount or precipitate.
Colloidal dispersion of one liquid in another are called emulsions. The next part of the experiment is related to Tyndall Effect which light are scattering by colloidal dispersion. The Tyndall effect was observed with 5 different solutions in beakers were labelled A,B, C, D and E. 1% of starch solution in beaker A shows that light can be dispersed while 5% of starch solution in beaker B shows that more light that can be dispersed due to the higher concentration. Even with a beam of light is focused on the dilute starch, the path of the beam is revealed by the light scattered to the side. For solution in beaker C, D and E with ferric hydroxide sol, sugar solution and potassium chromate respectively does not form the Tyndall effect. It can be seen that the light beam slightly dispersed through the solutions. It is proven that starch solution has the larger particle that cause the light beam to pass through, while the solutions for beaker C, D and E has smaller particles which cause only a little light dispersed through it.
CONCLUSIONS
In conclusion, the general properties of a ferric hydroxide sol, starch solution and some true solution can be identified through the experiment conducted. In dialysis experiment on part A, it shows that sugar solution and potassium chromate solution has the smaller particles compared to other solutions which allowed them to pass through the cellophane membrane thus gives the colour changes. Stability of ferric hydroxide solution is discovered with different electrolytes. It shows that PO4 produces higher amount of precipitate followed by SO 4 and Cl - produce the least amount of precipitate due to its low electronegative. Lastly, from the last part of experiment and theoretically it shows that starch solution exhibit the Tyndall effect through the dispersion of light beam while others does not exhibit the Tyndall effect due to the smaller particles which does not allowed the dispersion of light.
QUESTIONS
1. With appropriate examples, explain the difference between true solution, suspension and colloid.
True solutions is a homogenous mixture of two or more substance in which substance dissolved in solvent has the particle size of less than 10-9 m or 1nm. The solution cannot be filtered out but can be separated using the process of distillation. Simple solution of sugar in water is an example of true solution. A suspension is cloudy and heterogeneous and the component is greater than 1000nm which allows them to be filtered. The particles solution of suspension is big enough to see with naked eyes. When the suspension is allowed to stand the particles will separate out. The example of solution is the suspension of settled muddy water. Colloidal Solution is a heterogeneous mixture in which particle size of substance is intermediate of true solution and suspension between 1-1000 nm. While a suspension will separate out a colloid will not. Colloidal particles are small enough and cannot be seen through naked eye. They easily pass through filter paper but colloidal particles are big enough to be blocked by parchment paper or animal membrane.
2. What are gels and their types? For different type of gels explain their differences on dehydration and soaking properties.
Gels are classified into elastic gels and non elastic gels. The elastic gel turns to solid mass on dehydration which can again be converted into gel by addition of water followed by heating and cooling. The elastic gel that contact with water will absorb water and swell. This property is known as imbibitions. The non elastic gel turns to solid mass on dehydration but the solid mass cannot be converted again into gel after addition of water cooling. absorbed by the gel and the size remains when soaked into water.
The water is not
3. What kind of information can be obtained from light scattering experiment on colloidal particles in aqueous solutions? Explain your answer.
It distinguishes between true solutions and colloids as colloidal particles scatter light. If a beam of light such as flashlight or laser passes through the colloid, the light scattered by the colloidal particles and the path of the light therefore can be observed. When a beam of light passes through a true solution there is so little scattering of the light that the path of the light cannot be seen and the small amount of scattered light cannot be detected except by very sensitive instruments.
REFERENCES 1. Sullivan, R. (2012, June 3). Fehling Test. Retrieved November 11, 2016, from http://chemdemos.uoregon.edu/demos/Fehling-Test 2. P. Keusch, Demonstration Experiments on Video, "Fehling's Test." University of Regensburg, 6/3/11. http://www.uniregensburg.de/Fakultaeten/nat_Fak_IV/Organische_Chemie/Di ... 3. Leonard, M. (2014, March 12). Colloids. Retrieved November 11, 2016, from http://chemistry.tutorvista.com/physical-chemistry/colloids.html
