Cpt Manual Final - Copy.docx

Experiment No. 1 Objective: To purify water from mixture of water and ethanol using method of fractional distillation.

Theory: Fractional Distillation: Fractional distillation is a method of separating liquids with different boiling points. It is basically separation of a mixture into component parts or fractions. Chemical compounds are separated by heating them to a temperature at which one or more fractions of the liquid will vaporize. It uses distillation to fractionate. Generally the components have boiling points that differ by less than 25 degree centigrade from each other under a pressure of one atmosphere. If the difference in the boiling points is greater than 25 degree centigrade, simple distillation is deployed. When the mixture is heated, one liquid is evaporated before the other and is collected.

Apparatus: o o o o o o o o

Heat source such as hot plate Distilling flask Receiving flask Fractionating column Distillation Head Thermometer Condenser Standard Laboratory Glassware

Procedure: The apparatus is assembled as in the diagram. The mixture is put into the round bottom flask along with a few anti bumping granules and the fractionating column is fitted into the top. The fractional distillation column is set up with the heat source at the bottom on the still pot. As the distance from the still pot increases, a temperature gradient is formed in the column; it is coolest at the top and hottest at the bottom. As the mixed vapor ascends the temperature gradient, some of the vapor condenses and revaporizes along the temperature gradient. Each time the vapor condenses and vaporizes, the composition of the more volatile component in the vapor increases. This distills the vapor along the length of the

column, and eventually the vapor is composed solely of the more volatile component (or an azeotrope). The vapor condenses on the glass platforms, known as trays, inside the column, and runs back down into the liquid below, refluxing distillate. The efficiency in terms of the amount of heating and time required to get fractionation can be improved by insulating the outside of the column in an insulator such as wool, aluminium foil or preferably a vacuum jacket. The hottest tray is at the bottom and the coolest is at the top. At steady state conditions, the vapor and liquid on each tray are at equilibrium. The most volatile component of the mixture exits as a gas at the top of the column. The vapor at the top of the column then passes into the condenser, which cools it down until it liquefies. The separation is more pure with the addition of more trays (to a practical limitation of heat, flow, etc.) Initially, the condensate will be close to the azeotropic composition, but when much of the ethanol has been drawn off, the condensate becomes gradually richer in water.

Theoretical Plates: The above explanation reflects the theoretical way fractionation works. Normal laboratory fractionation columns will be simple glass tubes (often vacuum-jacketed, and sometimes internally silvered) filled with a packing, often small glass helices of 4 to 7 mm diameter. Such a column can be calibrated by the distillation of a known mixture system to quantify the column in terms of number of theoretical plates. To improve fractionation the apparatus is set up to return condensate to the column by the use of some sort of reflux splitter .

Figure:

Result: Water is purified as a result of fractional distillation.

Experiment No. 2 Object: To purify water by practicing simple distillation method.

Theory: Simple distillation: Simple distillation is a procedure by which two liquids with different boiling points can be separated. Simple distillation (the procedure outlined below) can be used effectively to separate liquids that have at least fifty degrees difference in their boiling points. As the liquid being distilled is heated, the vapors that form will be richest in the component of the mixture that boils at the lowest temperature. Purified compounds will boil, and thus turn into vapors, over a relatively small temperature range (2 or 3°C); by carefully watching the temperature in the distillation flask, it is possible to affect a reasonably good separation. As distillation progresses, the concentration of the lowest boiling component will steadily decrease. Eventually the temperature within the apparatus will begin to change; a pure compound is no longer being distilled. The temperature will continue to increase until the boiling point of the next-lowestboiling compound is approached. When the temperature again stabilizes, another pure fraction of the distillate can be collected. This fraction of distillate will be primarily the compound that boils at the second lowest temperature. This process can be repeated until all the fractions of the original mixture have been separated.

Apparatus: o o o o o o o o

Heat source such as hot plate Distilling flask Receiving flask Fractionating column Distillation Head Thermometer Condenser Standard Laboratory Glassware

Procedure: Check the calibration of the thermometer that is to be used. This can be accomplished by placing the thermometer in an ice bath of distilled water. After the thermometer has been allowed to reach thermal

equilibrium, place it in a beaker of boiling distilled water and again allow it to reach thermal equilibrium. If the temperatures measured deviate from the expected values by more than two degrees, obtain a new thermometer and check its calibration. Fill the distillation flask. The flask should be no more than two thirds full because there needs to be sufficient clearance above the surface of the liquid so that when boiling commences the liquid is not propelled into the condenser, compromising the purity of the distillate. Boiling chips should be placed in the distillation flask for two reasons: they will prevent superheating of the liquid being distilled and they will cause a more controlled boil, eliminating the possibility that the liquid in the distillation flask will bump into the condenser. Heat the distillation flask slowly until the liquid begins to boil. Vapors will begin to rise through the neck of the distillation flask. As the vapors pass through the condenser, they will condense and drip into the collection receiver. An appropriate rate of distillation is approximately 20 drops per minute. Distillation must occur slowly enough that all the vapors condense to liquid in the condenser. Many organic compounds are flammable and if vapors pass through the condenser without condensing, they may ignite as they come in contact with the heat source. As the distillate begins to drop from the condenser, the temperature observed on the thermometer should be changing steadily. When the temperature stabilizes, use a new receiver to collect all the drops that form over a two to three degree range of temperature. As the temperature begins to rise again, switch to a third collection container to collect the distillate that now is formed. This process should be repeated; using a new receiver any time the temperature stabilizes or begins changing, until all of the distillate has been collected in discrete fractions. Remove the heat source from the distillation flask before all of the liquid is vaporized. If all of the liquid is distilled away, there is a danger that peroxides, which can ignite or explode, may be present in the residue left behind. Also, when all of the liquid has evaporated, the temperature of the glass of the filtration flask will rise very rapidly, possibly igniting whatever vapors may still be present in the distillation flask.

Figure:

Experiment No. 3 Object: To prepare methyl orange.

Therory: Methyl orange is a pH indicator and due to its clear color change it is very often used in titrations. Methyl orange changes color at the pH of a mid-strength acid and is usually used in titrations for acids. Unlike a so called universal indicator, methyl orange does not have a full spectrum of color change, but has a sharper end point. Methyl orange is prepared from sulfanilic acid and N,N-dimethylaniline. The first product obtained from the coupling is the bright red acid form of methyl orange, called helianthin. In base, helanthin is converted to the orange sodium salt, called methyl orange. Dyes are used to give colors to substances, especially fabrics. Chromopohores, functionalgroups that absorb light, give color to these dyes. The most common chromophores are azo, nitro, and carbonyl groups. Auxochromes, functional groups that increase the intensity of the color, are also important parts of dyes. The most common chromophores are hydroxyl, amino, sulfonate, and carboxylate groups. Azo dyes have a nitrogen to nitrogen double bond as their chromophore. These dyes arecreated by taking a diazonium salt and adding it to a strongly activated aromatic system.In this experiment, you will synthesize methyl orange, an azo dye, by a diazonium coupling reaction with diazotized sulfanilic acid and N,N-dimethylaniline.

Basic Principle: Sulphuinic acid with sodium carbonate converted into sodium salt of p-aminobenzene sulphonate, it undergoes diazotization reaction in presence of nitrious acid to form diazonium chloride salt. The

diazonium ion then ionizes in aqueos solution giving sodium ion, chloride ion and internal salt and coupling occurs to yield methyl orange.

Procedure: In order to avoid any excess of a reagent that could decompose or cause decomposition and produce tar to contaminate our dye, you need to weigh the quantities of solid reagent very carefully to the accuracy of 0.05 g or better. In this experiment you will have to calculate for yourself some of the amounts of needed reagents. After you have calculated them, confirm your results with the instructor before proceeding. Dissolve 0.010 mole of sulfanilic acid (anhydride) in about 50 ml of a solution of sodium carbonate containing 0.010 to 0.0125 moles of sodium carbonate in a 125 ml Erlenmeyer flask. The solution is prepared by the stockroom and its strength is indicated on the bottle, but you must calculate the exact amount needed. Warm the mixture slightly to speed up dissolution. Test one drop of the solution to make sure it is alkaline. If not, add a small amount (1-2 mL) sodium carbonate solution and check the pH again. Then add 0.010 moles sodium nitrite and cool to 25 °C (room temperature). Put 40 g of ice in a 400 mL beaker and add enough hydrochloric acid of a 6M or a 12 M solution in order to provide a total of 0.030 mol HCl in your beaker. Add the sulfanilate solution prepared above in a fine stream while stirring continuously. Keep this solution cold in the ice bath at all times. It now contains your diazonium salt, which will decompose if it becomes warm. It is only partially soluble in the aqueous solution and will precipitate as a bluish-greenish solid. Prepare a solution of N,N-dimethylaniline (0.010 mol) in 0.010 mol of acetic acid in a 25 ml Erlenmeyer flask. Now add the dimethylaniline acetate solution slowly with constant stirring to the suspension of the diazonium salt. A dull, reddish-purple mass should appear. Now, VERY SLOWLY add about 30 mL of 1.0 M sodium hydroxide solution with constant stirring. Add the NaOH a few mL at a time. The addition should take 10 -15 minutes. The actual coupling reaction does not

occur until you add the NaOH. The reaction takes place best at about pH 7. Keep adding the NaOH until the solution becomes basic (blue to litmus.) If the sodium hydroxide is added too quickly, then free dimethylaniline will separate out as an oily phase. This then leaves an equivalent amount of the diazonium salt unreacted. This excess salt decomposes to brown tar on warming to room temperature and contaminates the otherwise beautiful crystalline orange dye. At the end of the coupling reaction a yellow-orange or golden color should be observed. The product will now be recrystallized from the reaction mixture. Heat the reaction mixture to boiling using your tripod and Bunsen burner. Everything should dissolve and the solution should be clear (though it will be highly colored). If all the material does not dissolve when the solution is heated to boiling, add more water as needed. Then, allow it to cool slowly to room temperature to crystallize and then place the flask in an ice bath to get it as cold as possible. Remember: do not stir or shake the solution when it is cooling. Allow the crystals to form in an undisturbed flask. They will be much purer and larger if they form slowly in a motionless flask. Filter the crystals by suction filtration, rinse them with 10 – 15 ml cold water and allow them to dry. Do not attempt to take the melting point of your methyl orange as it decomposes on heating. In order to observe the beautiful color change that occurs with our orange indicator dye, dissolve a small amount of the methyl orange in 2-3 mL of 95% ethanol and add 5% HCl a few drops at a time until you see the color change.

Results: Obtained product is said as methyl orange.

Experiment No. 4 Object: To prepare methyl red indicator.

Theory: Methyl red (2-(N,N-dimethyl-4-aminophenyl) azobenzenecarboxylic acid), also called C.I. Acid Red 2, is an indicator dye that turns red in acidic solutions. It is an azo dye, and is a dark red crystalline powder. Methyl red is a pH indicator; it is red in pH under 4.4, yellow in pH over 6.2, and orange in between, with a pKa of 5.1.[2] Murexide and methyl red are investigated as promising enhancers of sonochemical destruction of chlorinated hydrocarbon pollutants. Methyl red is classed by the IARC in group 3 unclassified as to carcinogenic potential in humans.

Basic Principle: As an azo dye, methyl red may be prepared by diazotization of anthranilic acid, followed by reaction with dimethylaniline:[3]

Procedure: Anthranillic acid is dissolved in glacial acetic acid with warming if necessary. The solution is cooled in ice bath with stirring until the acetic acid begin to crystallize. N-Butyl nitrile is added with stirring at such a rate that temperature do not rise. When the addition is complete the solution is allowed to stand for 15 minutes. Dimethylanaline is then added rapidly, the reaction mixture is stirred well and allowed to stand in ice water for at least 3 hours, but preferably overnight. The percipetated methyl red is filtered and washed with 10 ml of glacial acetic acid and dried in a vaccum dessicator over sodium hydroxide. The crude yield is 7-8g.

Result: Obtained product is said as methyl red indicator.