Lab Work 2: Quantitative Extraction of Organic Matter PDF

Laboratory Work 2 Quantitative extraction of organic matter from an aqueous solution by the extraction method Theoretical part Goals of the work - master the method of extracting organic matter from an aqueous solution by extraction with an org...

Laboratory Work 2 Quantitative extraction of organic matter from an aqueous solution by the extraction method Theoretical part Goals of the work - master the method of extracting organic matter from an aqueous solution by extraction with an organic solvent (extractant1). When analyzing environmental objects (surface water, soil, food, etc.), the polluting organic matter, as a rule, first has to be extracted from the object under study. The most common extraction technique is extraction. Objective of the work: To carry out the extraction of salicylic acid (C6H4(OH)COOH) from an aqueous solution (single extraction) using a separating funnel (Figure 1). Determine the degree of extraction of a substance from an aqueous solution and calculate the coefficient of its distribution between two fractions: Кg = Со / Сv, where Cv is the equilibrium concentration of the substance in the water layer; C o is the equilibrium concentration of a substance in the organic layer. Figure 1 - Separating funnel 1 Extractant - a liquid used to remove a solute from a solution 1  The essence of the method: An aqueous solution containing a dissolved organic matter (salicylic acid) is shaken in a separating funnel with an organic solvent immiscible with water. The organic matter passes from the aqueous phase to the solvent (extractant). The resulting solution of the recovered substance (salicylic acid) in an organic solvent is called the extract. The aqueous solution remaining after extraction with an underexposed substance is called raffinate. For the complete extraction of the substance from the raffinate, two to six extraction stages can be carried out sequentially. This process can be continuous. To do this, use a special Soxhlet extractor (Figure 2). Figure 2 - A schematic representation of a Soxhlet extractor 1: Stirrer bar 2: Still pot (the still pot should not be overfilled and the volume of solvent in the still pot should be 3 to 4 times the volume of the soxhlet chamber) 3: Distillation path 4: Thimble 5: Solid 6: Siphon top 7: Siphon exit 8: Expansion adapter 9: Condenser 10: Cooling water out 11: Cooling water in Equipment and chemical glassware A separating funnel with a volume of V = 100 ml Flask for distilling off the solvent (previously weighed on an analytical balance) (Check the mass of the flask with the teacher, mbefore ) 2 Condensate flask Beakers, V = 50 ml Аn installation for atmospheric distillation the same as in the laboratory work 1 Rubber bulb Technical scales accuracy 0.01 Paper or cloth napkins Lab tripod Plastic spoon Funnel Paper filter 3  Glass rod Automatic pipette, 100-1000 μl (for the teacher) A separating funnel on a stand rod is installed next to the distillation unit (one in each fume hood), a plastic spoon for sodium chloride, a funnel with a paper filter (to drain the extract from the separating funnel into a tared distillation flask), a glass rod for salt dissolution. Reagents. Sulfuric acid Н2SO4 (conc.), crystalline NaCl, solvents: hexane, chloroform, aqueous solution of salicylic acid (С6Н4(ОН)COOH) Step-by-Step Instruction The extraction work is carried out in a fume hood! Extraction procedure: Using Table 1, the student selects a solvent to be used to extract salicyolic acid from an aqueous solution. Explain why you chose this solvent. Principles for choosing an extractant: 1. Solvent should not have mixed with water (i.e. should not dissolve in water) 2. Solvent should be selective (selective, that is, to maximally extract a given substance from a possible mixture of substances. The higher the selectivity, the more completely and purely the given substance is extracted. 3. Solvent should have a large capacity in relation to the extracted substance (i.e. the solubility of the extracted substance in the extractant should be as high as possible). 4. Solvent should differ in its density as much as possible from the density of water. 5. Solvent should have minimum viscosity. 4 6. Solvent should be inexpensive. 7. Solvent should not be explosive. Performing extraction 1. Using a cylinder, pour 25 ml of an aqueous solution of the substance into a separating funnel then add 0.3 ml of Н2SO4 (conc.) (using an automatic pipette) then add 2 g of NaCl (using a plastic spoon) and stir until the salt dissolves. 2. After the salt has dissolved, 25 ml of the organic solvent selected for the extraction are added. 3. After closing the separating funnel with a stopper, mix the contents by vigorously shaking the funnel for 3-5 minutes. While shaking, the funnel is regularly turned upside down. By opening the tap, the excess pressure inside the funnel is released into the atmosphere. 4. After shaking, the aqueous and organic phases are allowed to separate (1–2 min). 5. The organic part (extract) is separated from the aqueous part (raffinate) at the interface. For this, use a tap.  If the extract is heavier than water (chloroform extract) and has collected in the lower part of the separating funnel, then it is poured through the bottom of this funnel into a tared (previously weighed on an analytical scale) round-bottom flask through an ordinary funnel with a paper filter.  A paper filter is used to prevent water from entering the extract.  It is possible, when draining from the separating funnel, a little (approximately 0.2-0.5 ml) of the extract can be left above the interface (again, to exclude the ingress of water into the extract collected in the distillation flask).  If the extract (hexane) is lighter than water and is collected in the upper part of the funnel, then initially the raffinate is poured into the glass, capturing a little (0.2-0.5 ml) of the extract. Then is collected the extract in a distillation flask as shown above. The extract in the distillation flask must be clear without water drops! 5  6. Salicylic acid is separated from the solvent by distillation (is used the same unit as in the laboratory work 1). The solvent is distilled off until it remains in the flask of 1-2 ml. 7. After distilling off the solvent, remove the distillation flask (flask for distilling off the solvent) from the thermostat and and carefully remove water from the surface of the flask (using filter paper). 8. Using a rubber bulb, remove the remaining solvent from. When removing solvent residues, the fume hood must be switched on! 9. The flask together with the substance should cool down and become of room temperature. 10. Weigh the flask with the substance (mafter), determine the mass of the extracted organic substance m1. 11. Calculate the degree of the extraction of the substance (RХ(1)) and the coefficient of its distribution (DХ) between the two phases in a single extraction (1): 𝑚1 𝑅𝑥 (1) = 𝑚𝑖𝑛 𝑚1 ⁄𝑉 2 𝐷𝑥 = (𝑚𝑖𝑛 − 𝑚1 )⁄𝑉1 where m1 is the mass of the extracted substance (x); min is the amount of substance (X) in the aqueous solution before extraction (this amount is determined by the concentration of the original control solution and V1); V1 is the volume of the initial aqueous solution of the substance; V2 is the volume of the extract, (1) is the first stage of extraction. 6 Table 1 – Solubility of substances in different solvent Solvent Water Chloroform Carbon tetrachloride Benzene Ethanol Acetone Hexane Density of the 1,000 1,498 1,595 0,879 0,790 0,792 0,660 solvent, g / cm3 Substance Solubility g / l Benzoic acid 3,400 187,3 55,70 77,66 283,6 429,6 13,30 Phenolphthalein 0,175 44,50 Traces 1,400 136,9 165,0 - Resorcinol 7,515 8,750 0,798 1,862 2928 1598 - Hydroquinone 71,72 26,71 0,009 0,248 393,8 191,4 - Salicylic acid 2,260 21,68 4,143 18,00 1528 313,0 1,150 2-naphthol 1,010 20,30 6,620 66,90 353,0 - - 7  Температуры кипения и показатели преломления некоторых органических веществ Формула вещества Относительная 20 Вещество Т. кип., °С nD плотность Ацетон C3H6O 0,792 56,24 1,3591 Бензол С6С6 0,879 80,1 1,5017 Бутанол-1 С4H9OH 0,810 117,7 1,3991 Диметилформамид (CH3)2NC(O)H 0,9445 153 1,4303 Диэтиловый эфир C4H10O 0,714 34,6 1,3520 Пропанол-2 CH3CH(OH)CH3 0,7851 82.4 1,3774 Петролейный эфир 0,650 - 0,695 40 – 100 1,3660 – 1,3700 Толуол C₇H₈ 0,86694 110,6 1,4960 Хлороформ CH3Cl 1,498 61,2 1,4464( 18°С) Четыреххлористый ССl4 1,595 76,8 1,4631 ( 15°С) углерод Этилацетат C4H8O2 0.902 77 1,3725 Изопропиловый C3H8O 0,789 68,5-69,0 1,3678( 23°С) спирт Этиловый спирт C2H5OH 0,789 78,37 1,3614 Относи́тельной пло́тностью вещества называют отношение плотности исследуемого вещества к плотности эталонного вещества. В качестве эталонной жидкости чаще всего используют дистиллированную воду, плотность которой при +20 °C равна 998,203 кг/м3, а при температуре максимальной плотности (+4 °C) составляет 999,973 кг/м3. 8  Boiling points and refractive indices of some organic substances 20 Substance Formula of substance Relative density Boiling point, °С nD Acetone C3H6O 0,792 56,24 1,3591 Benzene С6С6 0,879 80,1 1,5017 Butanol-1 С4H9OH 0,810 117,7 1,3991 Dimethylformamide (CH3)2NC(O)H 0,9445 153 1,4303 Diethyl ether C4H10O 0,714 34,6 1,3520 Propanol-2 CH3CH(OH)CH3 0,7851 82.4 1,3774 Petroleum ether 0,650 - 0,695 40 – 100 1,3660 – 1,3700 Toluene C₇H₈ 0,86694 110,6 1,4960 Chloroform CH3Cl 1,498 61,2 1,4464( 18°С) Carbon tetrachloride ССl4 1,595 76,8 1,4631 ( 15°С) Ethyl acetate C4H8O2 0.902 77 1,3725 Isopropyl alcohol C3H8O 0,789 68,5-69,0 1,3678( 23°С) Ethanol C2H5OH 0,789 78,37 1,3614 The relative density of a substance is the ratio of the density of the test substance to the density of the reference substance. Distilled water is most often used as a reference liquid, the density of which at +20 °C is 998.203 kg/m3, and at the temperature of maximum density (+4 °C) it is 999.973 kg/m3. 9