hello everybody my name is Iman welcome back to my YouTube channel today we're going to tackle a practice problem set that relates to our separations and purifications lecture let's go ahead and get started the first problem says fractional distillation under atmospheric pressure would most likely be used to separate which of the following compounds now if you remember from lecture fractional distillation is the most effective procedure for separating two liquids that boil within a few degrees of each other so what we're going to do is we're going to look at the answer choices we're given and try to figure out which one has which two liquids were given as options have just a few degrees difference between each other a we have 40° and 10° C so this is about a 30° difference between these two liquids and their boiling points B we have 77 and 80° so this is just a 3° difference then we have 184 and 205 so this is about about 21° difference and then D is 184 and 100 so 84° C we're looking for two liquids that boil within a few degrees of each other ethyl acetate and ethanol boil well within 25 degre CS of each other and thus would make good candidates for fractional distillation making the correct answer for one B two says which of the following compounds would be most effective in extracting benzoic acid from a diethyl ether solution we have tetrahydrofuran aquous hydrochloric acid aquous sodium hydroxide and water now by extracting all right by extracting with sodium hydroxide benzoic acid is going to be converted to its sodium salt sodium benzoate and sodium benzoate unlike its conjugate acid it's going to dissolve in an aquous solution the aquous layer simply has to be acidified afterwards to retrieve the benzoic acid and so aquous sodium hydroxide is going to be our best option now answer Choice a is incorrect because diethyl ether and tetrahydrofuran are both non-polar and they're going to be missible we're looking for two imiss all right uh solvents hydrochlor hydrochloric acid is not going to transform benzoic acid into a soluble salt so this is also not a good answer choice and D water is incorrect because protonated benzoic acid has limited solubility in water now three and four are going to reference this table right here we see compounds and their RF factor in ether three says what would be the effect on RF values if TLC were run with hexane instead of ether as the uent well hexane is less polar than ether and therefore it's less likely to displace polar compounds absorbed to the silica gel this would decrease the distance these polar compounds would travel thereby decreasing the RF value so the correct answer here for three is going to be D it's going to D decase four says if these compounds were separated by column chromatography with ether on silica gel which would elute first so in column chromatography all right just like TL TLC the less polar compound travels most rapidly this means that whichever compound here has the highest RF value would travel most rapidly and would be the first to elute from the column and that's going to be one napthalene methanol right here and so the correct answer is going to be D all right so four is D perfect let's go on to five five says which of the following would be the best procedure for extracting AAL alahh from an aquous solution we have the answer choices essentially say single extraction two extractions three or four here's the point that we need to remember it's going to be more effective to perform four successive extractions with smaller amounts than to perform one extraction with a larger amount of ether we briefly touched on this in the lecture and so here it becomes really obvious that the correct answer for five is going to be D here six all right we're going to do six now sneak peek of my finger four compounds 1 2 3 and four are separated by chromatography techniques compound three is the most polar two is the least polar and then one and four have intermediate polarity now the solvent system is 85 to 15 ethanol to methylene chloride which spot on the card below likes likely belongs to compound 3 compound 3 is the most polar let's remember that and also let's look at our solvent system 85 to 15 ethanol to methylene chloride all right this is a good example of reverse face chromatography because the solvent system is polar based off of the ratios of ethanol to methylene chloride all right now the solvent system is polar which means that the most polar compound is going to travel the furthest up the card all right resulting in the largest RF this gives compound 3 all right the largest RF that's going to be this spot right here which corresponds to Spa a so six is going to be a s says supposed an extraction with methylene chloride here's the density is performed with the desired compound initially in brine here's the density of brine in a separatory funnel which layer would be the organic layer now because methylene is more is is denser than brine the organic layer is going to settle at the bottom of the funnel all right that means which layer will be the organic layer the bottom layer so 7 is B we talked about this when we talked about extraction and separatory funnels in the lecture now on to 8 8 says silica gel is most often used in thin layer chromatography what property does silica gel probably possess that makes it the most useful or makes it useful for this purpose we talked about this in lecture we said that silica gels are polar and polarity is used to selectively attract specific solutes within a non polar solvent phase now although silica gels have other properties this is the most important to thin layer chromatography it's polarity so eight is b nine says a mixture of sand benzoic acid napoline in ether is best separated by what all right what you notice from all these answer choices it's a couple of different separation techniques one followed by the other let's think about this in this question we have these three substances that have to be separated using a combination of techniques the first step should be really obvious because we want to remove that sand all right and we can remove that sand to solid by filtration so that's pretty easy first thing we do is going to be filtration to remove the sand then we have the remaining compounds benzoic acid and napthalene all right and they're still dissolved in ether now if the solution is extracted with aquous base extracted with aquous base I'm sorry the benzoate anion is formed and then it becomes dissolved in the aquous layer while nathene which is a non-polar compound is going to remain in The Ether that's good cuz then we can finally all right we can we can do the filtration and then we're just going to do basic extraction and when we extract those two parts now with napoline and benzoic acid finally evaporation of the ether is going to yield purified nap and so what we're doing is filtration then extraction and then evaporation and that is going to align the best with answer Choice B so nine is B beautiful 10 says simple distillation could be used to separate which of the following compounds simple distillation all right so let's remember what simple distillation is all right we covered this in lecture if you remember simple distillation is used if the boiling points are going to be under 150° C and are at least 25° C apart so under 150 this means we could automatically cancel out B cuz notice that degree right there 218 that is not below 150 so now we have AC and D to work with all right the answer here is going to be C all right remember below 50 at least 25° C apart here this is only 11° apart this right here is 69° apart all right and this one right here is only 3° apart all right the only one that meets our requirement for for simple distillation is C all right there the the boiling points are under 150 and they're at least 25° C apart all right so C is the only option that would be effectively separated by simple distillation beautiful 11 says in order to separate a biological effector from solution which chromatography technique would be the most effective all right so if you remember when we were talking about different column chromatographies we really focused on um Affinity chromatography and how Affinity chromatography using the target for the biological effector or a specific antibody would be very useful because then as you pass a solution you can have this biological effector bind to your beads that have receptors that will that will effectively bind it and then you can pass through it after separating everything else a following solution that will then unbind and then you can separate this biological entity that you are interested in and so the answer is going to be Affinity chromatography right Affinity chromatography using the target for the biological iCal effector or a specific antibody is going to work best in this case it will specifically bind the protein of interest and then keep it in the column till everything else is separated out and then you can follow it with some elutant that will release your protein of Interest so you can collect it at the end all right so 11 is C beautiful 12 says given a solution of insulin here's the molecular weight and Titan all right here's it molecular weight which chromatography technique would be the most effective for separating out usable molecules of Titan all right so because this solution is composed of a much larger molecule and a much smaller molecule you guessed it size exclusion chromatography would effectively remove that smaller insulin molecule into the fraction retained in the column and then allow this other material to be eluded all right and so size exclusion chromatography here is going to be your best choice 13 says the gas uent in gas chromatography and the liquid in paper chromatography are examples of which component of these systems very good definition question each of these is the mobile phase of the system in which solutes are dissolved and move the stationary phase in gas chromatography if you remember is usually a crushed metal or polymer and the stationary phase in paper chromatography is paper and so the gas Alum and the liquid here in both of these techniques gas and paper chromatography respectively are the mobile phase all right the mobile phase so 13 is b 14 says during gravity U gravity filtration a student forgets to heat the solution before running it through the filter after capturing the filtrate the student analyzes the sample via infrared spectr roscopy and finds none of the desired product in the filtr what likely occurred to the student product all righty so warm or hot solvent is generally used in gravity filtration to keep the desired product soluble right that's what we covered in lecture this allows the product to remain in the filtrate which can then be collected so in this case the student likely used a solvent that was too cold and the product probably crystallized out right the product should actually be present now in the residue all right so what we're looking for is an answer choice that describes that right that the product probably precipitated out in some form and now it's present in the residue as opposed to the filtrate and the best answer choice that encompasses that is going to be answer Choice C 14 is C 15 says lacto Farin a milk protein is a valuable antimicrobial agent that is extracted from pasteurized defatted milk milk utilizing a colum containing a Charged resin this is an example of which of the following chromatography techniques now because the lactoferrin proteins are likely to be charged as is the resin described in this question this is probably a good example of ion exchange chromatography that charged protein molecules are going to stick to the column while the remainder of the milk washes through and then after that's washed through we can we can later wash off the column and collect the part that we are interested in the protein molecules all right so this is probably all right an example of ion exchange chromatography 15 is B and with that we end our practice problem set and we end our playlist for MCAT organic chemistry we have covered everything that we need to know for the exam I really hope this playlist was helpful to you I wish you the best of luck on your exam I hope you do amazing other than that let me know if you have any questions comments concerns Down Below Good Luck happy studying and have a beautiful beautiful day future doctors