CHEM14.1 E5 Colloids

Experiment #5: COLLOIDS MANUNTAG, Monica Earl TUMIMBANG, Glenn Vincent Group 5, Chemistry 14.1, Ms.Fatima Cruz March 27, 2012 I. ABSTRACT A colloid is a type of mixture in which a substance is dispersed evenly over another, basing its definition on the particle size, which is from 1 to 100 nanometers or 10-9 meters. A colloidal system has two phases: the dispersing or continuous phase and the dispersed or internal phase. The former refers to the medium used while the latter are the particles present in the system. Sols are classified under colloids, a type of dispersion to which a solid is dispersed in liquid. Aerosols, a colloidal system in which a liquid is dispersed in either a solid or a gas, is also classified here. And finally, emulsions, a dispersion of liquid in liquid, is also considered as a type of colloid. This system can either exist in a solid, liquid, or gaseous state, and it has two properties: Tyndall effect or the ability of the particles to scatter light and precipitation or the formation of insoluble solid in liquid. Preparation of colloids may be done either through dispersion or condensation. During dispersion, large-sized particles are dispersed to break them down to colloidal size, an example of which is the addition of an emulsifying agent. On the other hand, condensation is a way of uniting moleculesized particles to form colloid-sized particles. The experiment aims to determine the differences between the various kinds of colloids, as well as the properties they exhibit. The experiment also aims to compare the two principal methods in preparing colloidal system, dispersion and condensation. III. KEYWORDS: Colloids, Solution, Suspension, Dispersed phase, Dispersing medium, Sol, Lyophobic, Lyophilic, Emulsion, Tyndall effect, Precipitation III. INTRODUCTION Colloid is a type of mixture in which a substance dispersed evenly throughout another substance, both of which existing either as a solid, liquid, of gas. These combinations of dispersion give us the different types of colloidal systems which include familiar examples like clouds, fog, mist, smoke, soap, milk, mayonnaise, whipping cream, and even blood. The objective of this experiment is to compare the difference between the two principal methods of preparing colloids: the method of condensation and the method of dispersion. Furthermore, the experiment will be able to determine the different types of colloids, as well as the properties they exhibit. IV. EXPERIMENTAL PROCUDURE For the preparation of colloids, first, fifty mL of water was heated until it reaches its boiling point then freshly prepared 1 M FeCl3 was added by dropping. Dropping was continued until a change in color can be observed. The solution was allowed to cool for use in the next procedure. A pinch of sulfur was added to 50 mL of water and then stirred. In another set-up, alcohol was heated in a water bath. A pinch of sulfur was added and then the solution was poured into a 50 mL beaker of water. The two set-ups were observed and compared. Next, the proponents placed 10 mL of water in a test tube and added 1 mL of oil while shaking. After observing, it was set aside for 1020 minutes. Then, 5 mL of concentrated soap solution was added and the test tube was shook. Again, changes that can be observed were noted. For the first part of preparation of colloids. light can be seen passing through the cloudy mixture. The observations were compared to distilled water as negative reference. The dimensions of its particles range from 1 to 100 nanometers.The next part of the experiment was the Alexander’s patriotic tube. Tyndall Effect SYSTEM OBSERVATION Negative. scattered Negative. light can be seen passing through the light green solution. the dispersion of liquid in liquid which we call emulsions. light can be seen passing through the cloudy white solution. Table 3. The solution turned cloudy Sulfur sol (in while particles of sulfur settled hot alcohol at the bottom. Precipitation PRECIPITANT OBSERVATION Less was formed 1 M NaNO3 Least precipitate formed 1 M Na2SO4 Most precipitate formed 1 M Na3PO4 VI. There are several kinds of colloids. Next is the experiment on precipitation. scattered Negative. Positive. unboiled starch solution and soap solution. light passed through completely without being scattered. light can be seen passing through the cloudy white mixture. Dispersion is the process of breaking down large particles to colloidal size. DISCUSSIONS A colloidal dispersion is a type of mixture whose properties are between heterogeneous mixtures and homogenous solutions. The same was done to sulfur sol. First. foams-dispersion of . Sulfur did not dissolve in water. The third part of the experiment was the preparation of colloids. 10 drops of 1 M Na2SO4 to the second and 10 drops 1 M Na3PO4 to the third. and 1 mL of 1 M Potassium Ferrocyanide (K4[Fe(CN)6]) was added. We have the sols which is the dispersion of solid in liquid. light passed through Fe(OH)3 sol completely without scattering Sulfur sol CuSO4 sol Dilute milk Boiled Starch Solution Unboiled Starch Solution Soap Solution Distilled Water Positive. Fe(OH)3 sol was placed in a test tube and observed at a right angle against a beam of light form a flashlight. The dispersed phase are the particles itself while the dispersing phase is the medium or the solvent. scattered Positive. condensation is the process of making particles of molecular size unite to form particles of colloidal size. The solution was immediately pured into a test tube and was set aside for the agar to cool into gel. boiled starch solution. dilute evaporated milk. EXPERIMENTAL RESULTS Table 1. Preparation of Colloids COLLOID OBSERVATION The color changed to brownish Fe(OH)3 sol orange. a few drops of phenolphthalein to turn it pink. and water) Two observable layers can be observed with oil on top of Oil (in water) water. the dispersed phase and the dispersing phase. Fe(OH)3 sol was placed in three separate test tubes with 2 mL of solution. dispersion of liquid or solid in gases known as aerosols. light passed through completely without being scattered. Sulfur (in Some particles settled at the water) bottom while others floated. On the other hand. which is the Tyndall effect. Two drops of 1 M NaOH. The test tube was corked and let stand for an hour. light passed through completely without being scattered. Colloids may be prepared through dispersion or condensation. It has two phases namely. scattered Negative. A cloudy yellow layer (water and oil) formed beneath the Oil (in soap bubbly and green soap and water) solution. Examples of these are grinding and adding an emulsifying agent. Table 2. copper sulfate solution. The first test tube was added with 10 drops of 1 m NaNO3. a small amount of agar was dissolved in 15 mL of boiling water. V. Positive. They were then observed for the amount of precipitate present. sulfur sol. due to the presence of base. the oil droplets started to gather on top of the water. Precipitates of varying quantities formed on each test tube. The next part was the experiment on the Tyndall effect. Why is sulfur not soluble in water? What kind of colloidal dispersion is a sol? The basic principle in solubility. a base indicator. boiled starch solution. the shape of the sulfur (S8) has a large surface area for the solvent to dissolve. Also. was made. dilute milk. SO4 came next while NO3 has the least. therefore stabilizing the interface between the oil and the water in the suspension. enabled the immiscibility of sulfur to water. The soap solution was then added and chemically interacted with both the oil and the water. but after leaving it for some time. soap solution and distilled water. The next part of the experiment is the Alexander’s Patriotic Tube. dilute milk. the same principle is used in soap to remove grease in dishwares and other objects for cleaning. whiteyellow and blue. forming a distinct layer. The less . VII. H2O and FeCl3 formed Fe(OH)3. On the other hand. It acted as an emulsifier. The second part of the experiment involved the dispersion of liquid in liquid or emulsion. Interestingly. and boiled starch solution exhibited Tyndall effect. did not mix well with the dispersing medium or water. At first. a type of colloid where liquid is dispersed in solid. In the first part of the experiment. The systems that exhibited Tyndall effect were the following: Sulfur sol. a substance that stabilizes an emulsion. the oil formed scattered droplets in water.liquid in solid and gels which is the dispersion of liquid in solid. Since water is polar while sulfur is not. unboiled starch solution (+/-) and soap solution should have exhibited Tyndall effect while the CuSO4 sol and the distilled water are the only ones that will not exhibit Tyndall effect. the Fe(OH)3 sol. A sol is a type of colloid of very small solid particles dispersed in a liquid that retains the physical properties of a liquid. the colloid medium or the particles of Fe(OH)3 sol and the particles of the sulfur sol. Three layers have been formed: pink. It is a lyophobic (solvent-hating) suspension of solid particles (1-1000 nm in size) in a liquid. This is because according to the solubility rules. The bottom part was pink caused by phenolphthalein. The last part involves precipitation. 2. That is why sulfur particles either settled at the bottom or floated. like dissolves like. How would you account for the observation in procedure IA-b2? Sulfur is a nonpolar crystalline structure which makes it harder to dissolve in water under normal conditions. the two did not mix. and was later added with soap solution. copper sulfate solution. Theoretically. GUIDE QUESTIONS & ANSWERS 1. Oil was mixed with water. The arrangement of layers is made such that way due to the densities of the ions and compounds in the system. Fe(OH)3 and sulfur are insoluble in water. These are the reactions involved in each test tube: Fe(OH)3 + 3NaNO3 ----> Fe(NO3)3 + 3NaOH 2Fe(OH)3+3Na2SO4 ----> Fe2(SO4)3 +6NaOH Fe(OH)3 + Na3PO4 ----> Fe(PO4) + 3NaOH The quantity of the precipitates formed is based on the charges of the ions that will attach to the Fe3+. The bluish part called Prussian Blue was made from this reaction FeCl3 + K4[Fe(CN)6]KCl + Fe4[Fe(CN)6]3. sulfur in hot alcohol and water partially dissolved sulfur since ethanol is less polar and heated as well. On the other hand. Gel. Since the PO4 is the most electronegative among the others. no scattering was observed with the Fe(OH)3 sol. it yielded the most prominent precipitates. A lyophobic colloid was formed when the sulfur-alcohol mixture solution was added to water. colloid. This structure is called micelle. the soap. And finally. The upper layer. namely solution. This layer is Fe4[Fe(CN)6]3 or Prussian blue. The Tyndall effect is used to tell the difference between the different types of mixtures. they are physically combined so we may also separate them by physical means like undergoing dialysis. VIII. we may say that a sample is a colloid. covers and stops the oil from separating from the water molecules. and phenolphthalein. which is blue in color. CONCLUSION & RECOMMENDATIONS Colloids are mixtures wherein a substance is dispersed throughout another. 3. What ions/compounds are responsible for the different colors observed in the Alexander’s patriotic tube? There were four observable layers in the Alexander’s patriotic tube. Through testing Tyndall effect and observing precipitation.g. which is a highly insoluble substance but tends to form colloids. Below are summaries of the types of colloids and the differences between colloid. The bottom gelatinous layer is composed of agar. the water molecules is attracted to these lipophilic ends and therefore. It is important for us to know the properties of colloid that differentiate it from solutions and suspensions. was formed from the reaction of ferric chloride with potassium ferrocyanide. temperature and polarity may also affect a colloidal system.polar ethanol was able to dissolve the sulfur under the presence of heat. 4. yellow in color. which is seen as pink (due to the presence of a base and a base-indicator). exhibiting a miscibility with the oil. 5. This is exhibited when dust particles are seen in the air when sunlight strikes them or when the lights emitted by the headlights from a car on a dusty road can be seen. It is recommended in this experiment to calculate exact amounts of reagents to obtain results close to the theoretical yield. the air we breathe and even in nature. What causes Tyndall effect? Tyndall effect is the effect of light scattering on particles in colloidal systems. Tyndall effect and precipitation) make colloids different from solutions and suspensions. On the other hand. Colloids are everywhere. What is the role of soap solution in the oil emulsion prepared in procedure IB? The presence of polar and nonpolar ends in a soap solution bridged the immiscibility of oil and water. the topmost layer. Aside from that the nature of substance involved. We may find it from the food we eat. Following the procedures strictly in this experiment can help achieve theoretical results. The soap is called the emulsifying agent. Their distinct properties (e. is from the excess ferric chloride. NaOH. Since these are mixtures. The transparent part above it is caused by the chlorine entering and dispersing to the matrix of the gel. solution and suspension: . In the molecular point of view. having a lipophilic end. Give an explanation for the results obtained in procedure II. and suspension. It is caused by reflection of light by very small particles in suspension in a transparent medium. REFERENCES Brown.IX. th E. Laboratory manual in general chemistry (2006 ed. I hereby certify that I have given substantial contribution to this report. Manila. Chemistry: The Central Science (9 ed.. Glenn Vincent . © 1993-2006 Microsoft Corporation.).). H.. T. Philippines: University of the Philippines Manila Microsoft ® Encarta ® 2007. Singapore: Pearson Education (Asia) Pte Ltd. Manuntag.. Monica Earl Tumimbang. E. Bursten. L. All rights reserved. B. Committee on General Chemistry (2006). Lemay Jr.