Experiment Experiment No. 5 Colloids Cuizon, Marc Christian Dizon, Tristan Gabriel Maglasang, Glenn Michael Taotao, Anna Group 5, Chem 14.1, WEG1, Prof. Ralph Julius Mendoza March 18, 2009 Experime Experiment nt 5 is divided into three parts. The first part is the preparatio preparation n of two types of colloids, a sol and an emulsion. The second part consists of the preparation of the Alexander’s Patriotic Tube, which also has another type of colloidal suspension, a gel. The properties of different colloids are also observed after their preparation by observing the Tyndall effect and the amount of precipitation formed when added with different substances. Keywords: colloid, sol, emulsion, dispersion, lyophilic, lyophobic, Tyndall Tyndall Effect, precipitate, patriotic tube, coagulation
Introduction Colloids are kinds of chemical mixtures whe where a subst ubstan anc ce is disp isperse rsed eve evenly nly througho throughout ut another another.. This is one advantag advantage e of colloi colloids, ds, becaus because e colloi colloid d partic particles les are bigg bigger er than in a solution. solution. They are very tiny that is why they are easy to be dispersed evenly and thus, maintaining homogenous homogenous appearance. appearance. But also, they are also big enough to scatter light and not be dissolved. dissolved. Because of of these properties they they are important not only in the field of chemistry but also for the development of the standards in our daily living. Colloids have been of outstanding importance for the progress of the different products and process for a long time. The experi experimen mentt aims aims to discov discover er the variou various s characteristics of colloids – its properties, types and uses in the field of chemistry through the diff iffere erent pro procedur edure es perfo rformed rmed in thi this experiment.
Experimental Part I. Preparation Preparation of Colloids A. Sol 50mL of water was heated until it started to boil. 1M FeCl 3 was added drop by drop until a change change in colour colour was observed observed.. The solution solution was allowed to cool and was set aside. 5-mL alcohol was heated in a water bath and and a pinc pinch h of sulf sulfur ur was was diss dissol olve ved d in the the alco alcoho hol. l. The The solu soluti tion on was was then then pour poured ed with with stirring to 50-mL water. A pinch of sulfur powder was dissolved in another beaker containing 50-mL water. This solution solution was compared compared with the 5-mL alcohol alcohol and sulfur solution.
Chem 14.1,Colloids
B. Emulsion 1.0mL of oil was added with shaking to a test tube containing 10mL water. It was then left standing standing for 10 mins. After observing observing,, 5mL of conce concentr ntrate ated d soap soap soluti solution on was adde added d with with shaking to the mixture. It was observed again. Part II. Alexander’s Patriotic tube 15mL of water was heated to boiling and agar was dissolved in it followed by 2 drops of 1M NaOH, a number of drops of phenolphthalein phenolphthalein (unti (untill it turns turns pink), pink), 1mL 1M K4[Fe(CN)6]. The The mixture was immediately poured into a test tube and allowed to settle into a gel after which 1mL of 0.1 M FeCl 3 was poured in the test tube. The test tube was corked and was left to stand for an hour. Part III. Properties of Colloids A. A. Tynd yndall all Effec Effect t The solution prepared at the beginning of the experiment, Fe(OH) 3 sol, was placed in a test test tube tube and and placed placed against against a beam beam of light light coming through a small hole. The path of light was obser observed ved.. This This proced procedure ure was repea repeated ted using different systems: the alcohol and sulfur solution solution (prepared (prepared earlier), earlier), CuSO4 sol., sol., dilute dilute evap evapora orated ted milk, milk, boiled boiled starch starch sol., sol., unboi unboiled led star starch ch sol. sol. And, And, soap soap solu soluti tion on.. Each Each of the the systems’ results were compared using the result for distilled water as a negative reference. B. Prec Precip ipit itat atio ion n 2mL 2mL of Fe(OH Fe(OH))3 sol, prepared prepared earlier earlier,, was added to three 10mL test tubes. In the first test tube, 10 drops of 1M NaNO 3 was added. Then, 10 drops of 1M Na 2SO4 was added to the second and to the third, 10 drops of 1M Na 3PO4 was added. The precipitation formed in each test tube was compared relative to one another.
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Results In the preparation of the Fe(OH)3 sol, FeCl3 was observed to be dispersed in hot water. In the two sulfur solutions prepared, the one with hot alcohol and the one without, the sulfur did not dissolve. However, in the solution containing alcohol, the water became murky. The mixture containing oil and water was observed to have two layers with oil forming a layer above the water. While the mixture containing oil and soap solution was observed to have mixed into a murky substance. In the preparation of the Alexander’s Patriotic tube, four separate layers of four different colours were formed, pink, white, yellow and blue. The different ions/compounds in the pink gel reacted when the last reagent, FeCl 3, was added. In the observation of the Tyndall Effect in the different systems, the following results were obtained: Fe(OH)3 Sulfur sol CuSO4 sol Dilute milk Boiled starch sol Unboiled starch sol Soap sol Distilled H2O Table 1-Tyndall Effect -light was not scattered -light was scattered
In the last part of the experiment, the three Fe(OH) 3 solutions with three different precipitants yielded the following observations: Precipitant Precipitate 1M NaNO3 Least amount 1M Na2SO4 Na3PO4> Na2SO4 > NaNO3 1M Na3PO4 Greatest amount Table 2.Amount of precipitate VI.Discussion Matter is classified as either a pure substance or a mixture. Pure substances can either be an element (substance made up of only one kind of atom) or a compound (a combination of two or more elements that can only be separated chemically). On the other hand, mixtures are materials made by combining different compounds that will not react with each other chemically. This form of matter can be separated by physical or mechanical processes. Matter on earth is often found as a
Chem 14.1,Colloids
mixture. Most pure substances must be separated first from other substances to obtain them. When separating a compound from another compound, one may find it dissolved, suspended or dispersed in another compound. When a compound is dissolved in another compound, a homogenous mixture, a mixture having uniform properties, is obtained. This mixture is called a solution where the dissolved substance is a solute and the substance that dissolves it is a solvent. Heterogeneous mixtures on the other hand do not have the same composition, properties, and appearance. The nature of a substance affects its solubility. Polar solutes are soluble only in polar solvents and the same goes for non-polar solutes. Like dissolves like. Colloids or colloidal suspensions are on the dividing line between solutions and heterogeneous mixtures. They are mixtures that contain particles larger than normal solutes but small enough to remain suspended in the dispersing medium. One type of colloid, a sol, is a lyophobic or ‘solvent-hating’ suspension of solid particles dispersed in either another solid or a liquid ‘solvent’. Sulfur was observed not to have dissolved in water because sulfur is non-polar whereas water is polar. Owing to the like dissolves like principle, sulfur is not soluble in water. Instead, sulfur stays suspended at the bottom and at the surface of the solvent. Alcohol, a slightly polar substance with slightly non-polar ends, dissolves in water. The structure of the alcohol used, ethyl alcohol, C2H5OH, is partly polar because of the hydrocarbon chain of C2H5 and it is partly nonpolar because of the hydroxyl group of OH. When the mixture of hot alcohol and sulfur was added in water, the alcohol dissolved in water, turning the medium cloudy, while the sulfur was left dispersed in the medium. The type of colloidal dispersion formed was a sol. An emulsion is another type of colloid suspension where a liquid solute is dispersed in a liquid or a solid medium. In the experiment, an emulsion of a liquid substance dispersed in another liquid was prepared. Oil is non-polar therefore, when it was mixed with water, a polar substance, it did not dissolve. As it has less density than water, it forms a separate layer above the water. The soap solution that was later added, has both polar and non-polar ends. Its structure contains a hydrophobic, non-polar hydrocarbon chain and also a hydrophilic, polar carboxylate group. The oil is a pure hydrocarbon so it is
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non-polar. The non-polar hydrocarbon tail of the soap dissolves into the oil leaving the polar carboxylate end of the soap molecules to stick out of the oil droplets. This carboxylate group then, dissolves into water. The soap solution acts as an “intermediary” between the oil and the water. It provided the polar ends for water and the nonpolar ends for the oil to form an emulsion between three substances. The same principle is similarly used in cleaning grease and oil from dishes. Since water alone is not able to penetrate the oil or grease because of opposite polarities, soap is used in cleaning dishes. Another type of colloid is a gel , a sol in which the suspended particles are organized in a loose, but definite arrangement, giving some rigidity and elasticity to the mixture, as in jellies. The Alexander’s Patriotic Tube that was prepared formed four different layers of different colours. At first, there was only a slightly alkaline solution of agar with phenolphthalein and K4[Fe(CN)6]. The phenolphthalein, a pH indicator, turned the substance pink as it indicates a basic substance (the alkaline solution). FeCl3 was added after it cooled and a separation of the substances was evident. The top layer, Fe(OH) 3, was formed as a product of the reaction of H2O and FeCl3. The blue layer was formed by the reaction of : FeCl3 + K4[Fe(CN)6]KCl + Fe4[Fe(CN)6]3. The 3rd, white layer was produced when an acidic layer of HCl was formed discharging the pink of the indicator. The 4th layer of pink is the remains of the original gel, which remains basic due to the NaOH. The ordering of each layer is due to the density of the ions/compounds present in each layer. Colloids exhibit properties that distinguish them from true solutions. One property of colloid systems is that they scatter light. If a beam of light, such as that from a flashlight, passes through a colloid, the light is reflected (scattered) by the colloidal particles and the path of the light can therefore 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 or detected except by very sensitive instruments. The scattering of light by colloids is known as the Tyndall effect which was first explained by the
Chem 14.1,Colloids
British physicist John Tyndall. In the experiment, the Tyndall effect exists only in systems that are colloidal. The colloidal particles that are suspended or dispersed in the system are responsible for the scattering of the light. Distilled water was used as a negative reference because it is a pure substance that does not exhibit the Tyndall Effect. Colloidal particles are frequently needed to be removed from the dispersing medium, as in the removal of butterfat from milk. But because colloidal particles are too small, they cannot be separated by simple filtration. One method of separating colloidal particles is by coagulation, where the colloidal particles are enlarged. The FeCl3 sol colloid was separated through three different precipitants. Due to the number of moles of Na and the anions from each precipitant, the amount of precipitate was affected. Each precipitant had the following reactions: •
FeCl3 + 3NaNO3 3NaCl + Fe(NO3)3
•
2FeCl 3 + 3Na2SO4 6NaCl + Fe2(SO4)3
• FeCl 3 + Na3PO4 3NaCl + FePO4 After the reaction, the colloidal particles coagulate, and precipitate out.
VI. Conclusion and Recommendations Colloids are mixtures that can either be homogeneous and heterogeneous. Their solutes are too small to be claimed as suspensions and too big to be claimed as solutions. Because of this, they could exhibit some properties similar to suspensions and properties similar to solutions. However, they can be distinguished from the two for they could exhibit properties such as Tyndall effect, adsorption and dispersion (caused by the bombardment due to repulsion of the molecules of dispersed molecules having the uniform charges or Brownian Movement ). Suspensions can become colloids if agents such as emulsifying agents and surfactants are introduced in the suspension. Examples are detergents, that can make dirt, oils and fats be dispersed in water and be washed away from clothes, and alcohol, that can disperse sulfur in water.
VIII. References Lewin, Seymour Z. “Colloid.” Microsoft® Encarta® 2009 (n.a).(n.d) Retrieved from http://wiki.answers.com/Q/What_are_the_ ions_or_compounds_responsible_for_the
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_different_colors_observed_in_Alexander %27s_Patriotic_tube March 15, 2009 (n.a).(n.d) Retrieved from http://www.elmhurst.edu/~chm/vchemboo k/554soap.html March 16, 2009 (n.a).(n.d) Retrieved from http://en.wikipedia.org/wiki/Tyndall_effect March 16, 2009 (n.a).(2007) Retrieved from http://www.infoplease.com/ce6/sci/A0857 436.html March 16, 2009 (n.a).(n.d) Retrieved from http://books.google.com.ph/books? id=BVpDI7n2M9gC&pg=PA646&lpg=PA6 46&dq=precipitation+in+colloids&source= bl&ots=gWFyLkgGpw&sig=KzAvqgtedKc y9Ji-ZnaYAow_zB8&hl=en&ei=55-_SalO5jC6gOWq42vDQ&sa=X&oi=book_res ult&resnum=5&ct=result#PPA649,M1 March 16, 2009 Brown, T.L., LeMay, H.E., Jr., & Bursten, B.E. (2000). Chemistry: The central science, 8th ed. New Jersey: Prentice – Hall, Inc.
I hereby certify that I have given substantial contribution to this report.
_______________________ Maglasang, Glenn Michael
______________________ Taotao, Anna
______________________ Cuizon, Marc Christian
_____________________ Dizon, Gabriel Tristan
Chem 14.1,Colloids
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