3.9 Separation of Solutins and Mixtures Chromatography Notes Key

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o Topic 3.9 - Separation of Solutions and Mixtures Chromatography (14.2-14.4) Learning Objective: SPQ-3.C Explain the relationship between the solubility of ionic and molecular compounds in aqueous and nonaqueous solvents, and the intermolecular interactions between particles. Chromatography provides a method of separating a mixture of solutions based upon polarity differences. The polarity differences are sometimes considered solubility as well. There are three types of chromatography. 1) Paper chromatography 2) Thin layer chromatography 3) Column Chromatography Paper Chromatography (MOST COMMON IN AP CHEMISTRY) Methodology for paper chromatography: 1) Alineis drawn (typically in pencil) near the end of the strip of paper. 2) A drop of the sample to be separated is placed on that line. 3) The paper is placed in an {ideally) sealed container with a shallow layer of solvent where the bottom of the paper is touching the solvent, but the line is not. ) WaloF memms ; 4} Time passes and the solvent and dyes will separate. i Water 5) Remove the paper before the solvent reaches the Hlart top of the paper. 6} Measure the height of the leading edge of the solvent and measure the leading edge of each dye. PAPER CHROMATOGRAPHY ANALYSIS e The same compound will move at the same rate relative to the same solvent on different trials. e Different compounds will have an at least slightly different polarity to other compounds so the Rf factor will differ between compounds. The mare similar in polarity the sample is to the solvent the farther it will travel. Polar water will have polar samples travel far, and nonpolar samples travel a short distance. Nonpolar benzene will have polar samples travel a short distance, and nonpolar samples travel far. Identification of a sample is possible by comparing Rf values- NOT COMPARING DISTANCES. The stationary phase is the paper and the mobile phase is the solvent. > st In the image, the mixture does NOT contain Dye 2 as there is not a yellow dot in the mixture column. It does contain BOTH Dye 1 and Dye 3. It is not uncommon for dyes to have multiple parts which would look >, unsaaienn |ike multiple dots at different distances from the baseline. > Pasaliew ows e
1) 2) 3) 4) Column chromatography Column chromatography also separates a mixture in solution. F Methodology for column chromatography Thin Layer Chromatography Thin layer chromatography is extremely similar to paper chromatography except the separation occurs on a thin layer on a sheet of plastic. The layer is typically silica or alumina which are extremely polar. Though this is not always true. Thin layer chromatography can be used to separate some samples that are not colored to the naked eye. UV light is used with a solvent that will fluoresce under UV light to see the substances. The dark spots are where the components of the mixture are. This method is frequently used with amino acids, so expect this topic when the question also references biological systems. ¥ ® ® . # L4 L] WMo 348 M2 5 Lafore symying with ninhydin after spraying with ninfiyciin Thin Layer Chromatography Analysis The same compound will move at the same rate relative to the solvent on different trials. Different compounds will have an at least slightly different polarity to other compounds so the Rf factor will differ between compounds. Typically, the more nonpolar the sample is, the farther it will travel. Typically, the more polar the sample is, the shorter it will travel. The leading edge must still be identified and not allowed to reach the top. Identification of a sample is possible by comparing Rf values- NOT COMPARING DISTANCES. K acdi v A W S Steel wool is placed at the bottom of a burette to prevent the gel from escaping. A burette is filled with very polar silica or alumina gel. (usually) The mixture that is to be separated is placed at the top of the burette and is flushed time and again with nonpolar solvent (usually). {(pour solvent, wait and watch, repeat) The mixture separates and each phase is collected in a beaker or flask one at a time. lfi -4t - -4 4 Changia fis bealer oncs thy yeliaw starts in drap brough.
St Elient Column Chromatography Analysis e Usually, the most polar parts of the mixture will travel the slowest and the least polar will travel the fastest. ® Once you have separated one part, you may use a new solvent to speed up the movement of the remaining part(s). e This is meant for separation more than analysis. }m Stationary phase Once separated, you could use a different method of chromatography to identify the component. e EliJ0tQ Distillation Distillation is another method of physically separating mixtures. Distillation separates substances based on differences in boiling point and intermolecular forces. Shown is a simple distillation apparatus. The starting liquid {15} in the boiling flask {2} is heated by a combined hotplate and magnetic stirrer {13} via a silicone oil bath (orange, 14). The vapor flows through a short Vigreux column (3}, then through a Liebig condenser (5), is cooled by water (blue) that circulates through ports (6 and 7}. The condensed liquid drips into the receiving flask {8), sitting in a cooling bath (blue, 16}. The adapter (10} has a connection (9) that may be fitted to a vacuum pump. The components are connected by ground glass joints {gray). Applications of distillation include: e Distillation of fermented beverages ® Desalination of salt water ® Separation of crude oil into fuels and other petroleum products {this often occur through fractional distillation} Typically, if the bolling points are close together, fractional distillation is a better technique to separate substances. Fractional distillation allows the vapor to condense and revaporize several times, leading to a better purification. With all types of chromatography, you will need to recognize which part of the system will interact with the materials being tested. Consider the intermolecular forces for all components.
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Practice 1) Which of the following is a most appropriate reason to perform column chromatography over paper chromatography? a} The sample is a mixture of strictly polar particles b) The sample is a mixture of strictly nonpolar particles The goal is to separate and recover the parts of the mixture d) The densities of the component parts of the mixture differ 2) Explain how two students could perform chromatography on the same mixture, the colored samples all move different distances, yet they can correctly identify the component parts. G Should e ‘Hhe same becaute Uk 1S oo vadio OF (he chstarce Hoveled ex. Lem «d. 00 et 0.5 Seoermnm | H.00cm 3) A student was performing paper chromatography and let the separation continue overnight. The student wished to determine if the mixture contained a substance with an Rf factor of 0.343 where: Rf = (distance travelled by the component)/(distance traveled by the solvent} a) What data would be affected by this error? Soluten would run ofF “he paper b) Explain the effect on the calculated Rf. Wradte reading - e would s nereake- ot gt AcC “{& (fl' ]0054’1 woulad Hranel FHhe lmgw oF Hu paper Final Pasition of Dye / Solvent on the left, and an incomplete image of the same mixture’s separation on / the right. The data on the left has a leading edge of solvent of 20.0 cm and // 4) The image shows the complete chromatography separation of a mixture / / the distance traveled by the dye was 8.0 cm. The data on the right shows the leading edge of salvent as 6.0 cm. What distance would you predict the 1 \ ] same dye to travel on the chromatography paper on the right? 4.8cm 5 6o foem _ 7 o c) 80cm " N d) Cannot be determined I() dem (f oem ] T A e, Griginal Posttion of Dye hromatography paper
5) Calculate the Rf for the following where the lines on the chromatography paper represent the starting point of the i dye and the final distance traveled by the solvent. a) CH,CH,CH,COOH Cole ¢} CH;OH d) CBH18 7} In paper chromatography, what physical property is most important to the separation? a) Density Pofarity . c) Size of particle 2. 9%m _ EZC"" 'OIS“ZD 28w d} Molar mass of particle 8} A distillation of several compounds was performed. Based on the physical property provided, place the substances in order of extraction. _ - Ol&sm 2 3em 6) Which of the following would travel the farthest in column chromatography? least polafl i Name Formula Boiling Point Acetone CH3COCHz | 56°C 2. Diethyl Ether | C2Hs0C:Hs | 34.6°C (B Ethanol Ca2lHs0H 784°C & /- Di{%’t%i ¢sbher 7 - Alltone 7 - Edhano |
Distillation EdPuzzle Directions Click on the page in Schoology titled “Distillation EdPuzzle.” Answer the questions below. You do not have to answer them online. 1. ____ Whywould he run cold water along the top? a) to help it condense back to a liquid b) because he cheated ¢) tomakeitclean 2. “There is a flame there but it is hard to see.” THIS IS NOT A QUESTION! 3. Why do you have to boil the colored water solution? 4. ___ Asthe water boils, it begins to __, causing it to change from a liquid, toa _. a) freeze, gas b} evaporate, gas ¢) condense, solid d} evaporate, liquid 5. What do you think would happen if a water solution and the food coloring had similar bolling points? 6. Why can this be difficult to do on a large scale? a) wateris not easy to distill b) itisn't difficult, it would work ¢) it takes a lot of energy 7. Summarize the process of distillation in 1-2 complete sentences.
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AP Chemistry Daily Videos 3.9 Separation of Solutions and Mixtures Chromatography Daily Video #1 | 1. Describe how chromatography is able to separate solutions based on Chromatography IMFs 2. Pause the video at 2:22 and attempt the problem, then evaluate how you did and identify any errors In & paper chromatagraphy experiment, & sample of 8 pigroent s separaled Into two components, X and Y, ag shown i 1he figure bolow. The surface of the paper Is moderataly potar. What can be canciuded about X and Y based on the experimental resulis? Filter Paper & Componenl X [ Component Y Pigment . Sample e Flexnne e =D Cthad a0 in @ N a8 hergpet molar puss Han ¥ foss. @ X b5 norg pala Gas ¥ ¥ fis o tavger sedin mass than X does (I) ) ¥ i3 mons petar Bt X, 3. Pause the video at 4:18 and attempt the problem, then evaluate how you did and identify any errors Agladent obtaing a sampla of purple food dys whish Is known to contain both red and tlue dyves dissolvad in a selution of Isopropyl alcohal, Sketeh an appropiiate lab selup to use In order for the student to separate thg o dyes. i ife blue dye Is fess polar than the red dye, which would we axpact to frave! the farthest on the nonpolar stationary phase?
Daily Video #2 1. Describe how distillation is able to separate solutions based on IMFs 2. Pause the video at 2:01 and attempt the problem, then evaluate how you did and identify any errors # Y H M u o HoH H H o1 P g ] flow Qom Com oGt R St Sl St Distillation 1t 0 n H H B H H Byl Acerate Btyl Acetate Arnixiura comalning squat nmbers of moles of ethyl acotuls and bulyl ncotala was soparatad using distiflation. Based on the diagranss shovn above, which of the following identiflas the sulistarce that would b Inltiafly prewent in higher concantration in the distiffate and cormactly oxplaing why thal oecurs? 3. Pause the video at 2:53 and attempt the problem, then evaluate how you did and identify any errors Amilxture contalning equal aurabers of moles of ettiy! aselato and bulyl nootate was separated using distiltation. Based on the diagrams shown above, which of the followlng identifios the substance that would e Inftially present in higher concentradion in the distiitate and correctly explafns why that oceurs? @ Febyh seastare, bucauss # has fowssr §-C bands to Broak @ Eihiyh noadate, Dasause it has o shnster corton chab s wraker Lando disfmeston forcas @ Syt ocstal, baresuss 1 has mero GC bonds to trask @ Bulyl acetate, becarust it bis & Jongey earhonehisin st wisher digpie-digels attactions 4, Pause the video at 3:37 and attempt the problem, then evaluate how you did and identify any errors Compound Formula Bolling Point*C. Dansity g/mi. butanel CH,0H 177 10,8098 Epnnlanol : CeHy OH 1318 0.8247 A student obiservas thal a mixiure of butans! and pentans! arg miscible, Using information It the tablo above, what technique could the student uge to separate the two components of the mixtura? Justify your answer.
227 3) 140 120 A 8100 Mou»/ [ 2 p £ 80 & o 5 = 401 20 A B c D O 5 10 15 20 25 30 35 40 45 50 Volume (mL) A student performed a fractional distillation of a mixture of two straight-chain hydrocarbons, C;H,; and CgH,g. Using four clean, dry flasks, the student collected the distillate over the volume ranges {A, B, C, and D) shown in the graph above. Over what volume range should the student collect the distillate of the compound with the stronger intermolecular forces? F = A L0 o palng pord = SO I c) C ) @D
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AP Practice Problems Solvent Front ‘‘‘‘‘‘‘ Solvent Bolling Point (" C) Relative Polarity PI‘OdUCtQ:\»‘ Pentane 36 0.1 Hexane 68 0.1 Origin Ethyl acetate 77 4.4 Methanol 65 5.1 N 1) The diagram above shows a thin-layer chromatogram of a mixture of products from a chemical reaction. The separation was performed using 50% ethyl acetate in hexane as the solvent {mobile phase} and silica gel as the polar stationary phase. On the basis of the chromatogram and the information about solvents in the table above, R which of the following would be the best way to decreas the distance that the products travel up the plate? rdgghjvt‘f aHf‘mw OF e pvisdad ks sowrh Showldd e cl.zfc.vm_fifizé a) Use pentane instead of hexane in the solvent. o CMJ{»%_ bic Po\ay ures soarne Decrease the percentage of ethyl acetate in the solvent. ¢) Increase the percentage of ethyl acetate in the solvent. | y\orig ea¢, @?QW‘ a0 eyt Wi e, d} Add up to 5% methanol to the solvent. ) al - ) Addupto 5% creoie aFfundy W\ Mere petor hasl &'h(»j( oCetad ¢ 2) A student obtains a liquid sample of green food coloring that is known to contain a mixture of two solid pigments, one blue and one yellow, dissolved in an agueous solution of ethanol. Which of the following laboratory setups is most appropriate for the student to use in order to separate and collect a substantial samptle of each of the two pigments? Thu laer Churopadog rophit = ide 1Pyt dafi”‘md” Comou ' rictusL