The Synthesis Of Alum Potassium Aluminum Sulfate - 1375 Words

The Synthesis Of Alum: Potassium Aluminum Sulfate Dodecahydrate (Research Paper Sample) Content: The Synthesis of Alum: potassium aluminum sulfate dodecahydrate (KAl(SO4)212H2O).Name of the studentExperiment performed on:AbstractThe experiment was intended to enable the students learn how to synthesize potassium aluminum sulfate dodecahydrate (KAl (SO4)212H2O), an alum. The process involved first reacting aluminum foil with excess potassium hydroxide solution. The resulting mixture was then filtered, and then mixed with dilute sulfuric acid. The reaction was allowed to proceed to conclusion after which the resulting mixture was cooled to allow the crystals to form. A dry container was weighed, and then the crystals stored in it. The container and the crystals were later weighed to determine the mass of the alum. The percentage yield of the experiment was found to be 93.24%.IntroductionProduction of alum involves both physical and chemical reactions. Alum refers to a crystal substance that is made up of cations of monovalent or trivalent metals. In other words, th e cations involved have 1+ and 3+ charges. This experiment is intended to synthesis an alum known as potassium aluminum sulfate dodecahydrate (KAl (SO4)212H2O). A hydrate is a molecular compound containing water of crystallization (Moody, 233). The objectives of the experiment include observing and recording the synthesis process a compound and calculating the percent yield of the synthesis.In the experiment, an aluminum foil was first reacted with excess potassium hydroxide solution. The resulting mixture was then reacted with sulfuric acid. The aluminum is a reactive element. However, the surface of aluminum is usually covered with a thin layer of aluminum oxide. Consequently, its reaction with acids is slow. However, aluminum reacts readily with basic solutions to form tetrahydroxoaluminate ion (Al (OH) 4- ). Consequently, aluminum foil was first reacted with excess potassium hydroxide in the experiment.ExperimentalAll safety precautions were observed before, during, and at the e nd of the experiment. Consequently, the students wore goggles before beginning the experiment. A small piece of aluminum foil was then obtained and weighed using an analytical balance (0.0001g). The foil was then rolled into a loose ball and placed in a 250mL beaker.Next, the first step of the synthesis was conducted while care was being taken to avoid spilling KOH solution on the clothing or skin. In this case, 25mL of 3MKOH solution was measured using a graduated cylinder. The beaker with aluminum pieces was placed in the hood. The KOH solution was then added slowly to the beaker. The reaction was left to proceed until all of the foil had dissolved. Buchner funnel and filter paper flask with filter paper was then set up in preparation for filtration later. The paper was moistened with a few drops of distilled water, and a vacuum drawn to seat the paper firmly on the filter support. The reaction mixture was then poured into the Buchner funnel-and-the filter flask set up while the v acuum was on and the filter paper seated firmly on the filter support. The filter paper was then rinsed with a small amount of distilled water. The beaker was then rinsed with distilled water and the filtered liquid poured back into the beaker. The solution was allowed to cool to near room temperature. The Buchner funnel and the filter flask were then cleaned. The funnel was prepared for later filtering using a new piece of filter paper.Next, the final step of the synthesis was conducted. In this case, 35mL of 3M H2SO4 solution was measured out using a graduated cylinder. The reaction mixture was then cooled to room temperature before proceeding. The sulfuric acid solution was then added to the beaker of liquid. In the process of adding the acid, the mixture was stirred. The mixture was boiled until the volume of the liquid in the beaker had reduced to about 50mL. The beaker containing the solution was then cooled. An ice bath was then prepared for the 250mL beaker containing the s olution. The beaker was then placed in the ice bath uncovered. The set up was left to allow the crystals to form. After the crystals had formed, the beaker was stirred to suspend the crystals. The crystals were then collected by pouring them into the Buchner funnel and the filter flask set-up. The crystals were then washed on the filter paper with 50mL of aqueous ethanol solution using vacuum filtration. A container was obtained and labeled with the initials of each student who performed the experiment. The empty container was then weighed, and the weight recorded. The crystals were then transferred to the container. The container was left open to the atmosphere to allow any remaining water and ethanol to evaporate. A few days later, the mass of the container and the crystals were measured. The appearance of the crystals was noted, and the observations recorded.ResultsTable 1 below shows the data obtained from the experiment:Table SEQ Table \* ARABIC 1: Data obtained from the exper imentMass of aluminum foil 0.985g Mass of empty container 21.79g Mass of container + alum 37.93g Using the data presented in the table above, the students obtained the actual yield of the aluminum. Table 2 shown below shows the results obtained from calculations done using the data shown in table 1.Table SEQ Table \* ARABIC 2: Table showing the actuals yield and the percentage yield of the synthesisMass of aluminum foil 0.985g Mass of empty container 21.79g Mass of container + alum 37.93g Actual yield of alum* 16.14g Theoretical yield* 17.31 g/mol Percent yield* 93.24% During the experiment, various observations were made. First, upon adding KOH solution to the beaker containing pieces of aluminum metals, the temperature of the beaker increased. In addition, bubbles of gases were seen rising up the beaker. The reaction involving sulfuric acid was also found to be leading to an increase in temperature. When sulfuric acid was added to the mixture obtained from the first step, a prec ipitate was formed. However, on further addition of sulfuric acid, the precipitate dissolved. The crystals formed were small and white in color. They also had a regular octahedral shape.DiscussionThe results of the experiment confirm that the method used in the synthesis of potassium aluminum sulfate dodecahydrate (KAl (SO4)212H2O) was appropriate since the alum was formed successfully. In the experiment, aluminum foil was reacted with KOH since aluminum reacts readily with basic solutions. This step is known as the dissolution step. The reaction of aluminum with an acid is slow. Consequently, its reaction with an alkali is preferred. Besides, KOH was used in order to incorporate the ions for both potassium and aluminum in one compound. The reaction is highly exothermic. Consequently, the temperature of the beaker rose. The overall equation for the reaction is as shown below:The bubbles seen rising up the beaker during the reaction between aluminum foil and KOH solution are as a res ult of hydrogen gas being given out during the reaction. The second stage of the synthesis process involved reacting dilute sulfuric acid with the product of the reaction in step 1 of the synthesis process. In this case, white precipitates were formed upon adding of the sulfuric acid. However, the white precipitates disappeared when more sulfuric acid was added. The precipitate was observed because aluminum hydroxide was formed. The hydroxide precipitated because it was displaced by K+ from the solution. The precipitate disappeared since further addition of the acid led to the reaction between the acid and aluminum hydroxide leading to the formation of aluminum sulfate. During the cooling process, aluminum sulfate and sulfuric acid reacted to form potassium aluminum sulfate dodecahydrate (KAl (SO4)212H2O) and water. All the reactions involved in the synthesis are shown in equations 1 to 4 shown below:1. Reaction of aluminum with KOH (the dissolution step)2 Al(s)+2 KOH(aq)+6H2O(l)2KA l(OH)4 (aq)+3H2 (g) Equation 1(Beran, 194)2. Initial addition of sulfuric acid (precipitation of Al(OH)3)2 KAl(OH)4 (aq)+ H2SO4 (aq)2Al(OH)3 (s)+K2SO4 (aq)+2 H2O(l) Equation 23. Further addition of sulfuric acid (dissolving of Al(OH)3)2 Al(OH)3 (s)+H2SO4 (aq)Al2(SO4)3 (aq)+6H2O(l) Equation 34. Precipitation of alum on coolingK2SO4 (aq)+ Al2(SO4)3 (aq)+24H2O(l)2KAl(SO4)212 H2O(s) Equation 4The percent yield of the synthesis of 2KAl (SO4)212 H2O was found to be 93.24%. It was expected that the experiment would yield 100%. The observed deviation of the actual yield from the theoretical yield is attributed to the various errors involved in the experiment. Factors affecting the percent yield include the following: The presence of impurities in the reactants used, the possibility of some products remaining in the purification vessels, occurrence of side reaction leading to formation of by-products, and error in taking the measurements.The presence of impurities is likely to result in the actual yield being higher than the theoretical yield. It is caused by poor purification. Some products may also remain on the filter paper especially if the paper is poorly rinsed with distilled water. Side reactions that involve the reactants are likely to result in low actual yield.A synthesis reaction is a type of reaction whereby two or more chemical species combine to form a more complex product. The reactants involved in the synthesis reaction are either elements or compounds. In this experiment, synthesis rea...