I am doing a chemistry experiment on how the polarity of the solvent sugar water, salt water and tap water affects the RF value in chromatography. I will be separating blue, red and yellow food colouring. Does anyone have a hypothesis on how the polarity of the solvent affects the RF value?
How does the polarity of a solvent affect RF value in chromatography?
What am I supposed to expect and why? Unfortunately, these are the materials provided and we are not allowed to use any other materials. I think I've also gotten the question wrong. I meant to say, how does the solubility of the solvent affect paper chromatography. What is your solid phase? What material will you be packing your column with, or are you using thin layer chromatography or paper chromatography? The more polar analytes will stick to the paper more. The less polar ones will stick less.
We expect that a more polar solvent will result in smaller Rf values because polar food coloring molecules will partition more readily into a more polar mobile phase. The problem with this experiment is the solvents are way too polar to get proper partitioning. Which type of chromatography will you be doing?
In thin layer chromatography, a solvent is mixed with a solute. Knowing the basic principles of polarity, polar will attract versus non polar which will repel. In thin layer chromatography, if the solute and solvent attract because of polarity, the spots formed under UV light will be tightly packed together. If they repel, they will then spread out more, and once an Rf ratio to front value is computed, you can interpret your results. Thank you :.
Update: I am doing Paper Chromatography. Update 2: Unfortunately, these are the materials provided and we are not allowed to use any other materials. Answer Save.
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Chemistry Organic Chemistry Lab. For my developing solvent, I used hexane:ethyl acetate. For my reference spot, I mixed some salicylic acid and ethyl acetate.
And for my test spot, I used some impure aspirin and ethyl acetate. I got 3 spots total, 1 spot for my reference and 2 spots from my impure sample of aspirin. Reference spot traveled 2. Was the hexane:ethyl acetate too polar? Can someone explain to me what my values mean??? Add comment. The Rf retention factor depends on many variables, and should not be taken as an absolute value. It will vary from experiment to experiment, from location to location, etc. So, not getting the exact value reported shouldn't be of such concern.
Probably the most likely possibility is how your tank was equilibrated, if at all. Here are some other concepts to contemplate.
In TLC, the stationary phase silica is fairly polar, so more polar molecules will be retained longer and have smaller Rf values. Vice versa for non polar molecules. Since your experimental Rf value is somewhat greater than the one reported in the handout, this suggests that your spot ran further up the plate than expected, thus suggesting greater polarity of the mobile phase.
Is it possible that you prepared the mobile phase as ethyl acetate : hexane instead of the other way around? Asking if the hexane:ethyl acetate is too polar is an appropriate questions, and does agree with the science of TLC and Rf values, as explained above. Again, if you look in the literature for TLC results of aspirin and salicylic acid, you will find varying Rf values, so one shouldn't be overly concerned about it.
These values will vary with temperature, humidity, and most importantly, how the tank is equilibrated with mobile phase.
Ask a question for free Get a free answer to a quick problem. Find an Online Tutor Now Choose an expert and meet online.What does a high RF value mean in paper chromatography?
Factors That Affect RF Values in Thin Layer Chromatography
It is used in chromatography to quantify the amount of retardation of a sample in a stationary phase relative to a mobile phase.
See Full Answer. What does it mean to have a high RF value? A high Rf Ie 0. A low Rf value 0. Retention time RT is a measure of the time taken for a solute to pass through a chromatography column. It is calculated as the time from injection to detection. The RT for a compound is not fixed as many factors can influence it even if the same GC and column are used. Rf values. The Rf value of a particular compound is always the same - if the chromatography has been carried out in the same way.
This allows industry to use chromatography to identify compounds in mixtures. What does a small RF value tell you? Beta carotene is carried the furthest because it is highly soluble in the solvent and because it forms no hydrogen bonds with the chromatography paper fibers.
Chlorophylls are bound more tightly to the paper than the other two, so they travel the shortest distance. Vines make great screens. Climbing Roses. Train climbing roses over fences, walls, pergolas and gazebos. Cherry Laurel.
Cherry laurel is an evergreen shrub or small tree native to the southeastern United States. Boxwood are easy to grow and maintain. Japanese Holly. Fan Palm.What role does polarity play in chromatography?
Polarity has a huge affect on how attracted a chemical is to other substances. The larger the charge difference, the more polar a molecule is. You will find that as you increase the polarity of the solvent, all the components of the mixture move faster during your chromatography experiment.
See Full Answer. Why does the solvent move up the paper? Non-polar molecules in the mixture that you are trying to separate will have little attraction for the water molecules attached to the cellulose, and so will spend most of their time dissolved in the moving solvent.
Molecules like this will therefore travel a long way up the paper carried by the solvent. Chlorophyll is a green pigment that gives most plants their color. The reason that it is green is because it absorbs other colors of light such as red and blue, so in a way the green light is reflected out since the pigment does not absorb it. The amount that each component of a mixture travels can be quantified using retention factors Rf. The retention factor of a particular material is the ratio of the distance the spot moved above the origin to the distance the solvent front moved above the origin.
In chromatographythe retardation factor R is the fraction of an analyte in the mobile phase of a chromatographic system. In planar chromatography in particular, the retardation factor R f is defined as the ratio of the distance traveled by the center of a spot to the distance traveled by the solvent front.
Is silica gel polar or non polar? The presence of these hydroxyl groups renders the surface of silica gel highly polar. Thus, polar functionality in the organic analyte interacts strongly with the surface of the gel particle and nonpolar functionality interact only weakly. Is ferrocene polar? In most column and TLC the stationary phase has a very high polarity and the mobile phase has a lower polarity.
Ferrocene is less polar then acetylferrocene. This means that ferrocene will like, or have a higher affinity to the less polar mobile phase than the more polar stationary phase. Is silica polar? In chemistry, silica gel is used in chromatography as a stationary phase. In this application, due to silica gel's polarity, non- polar components tend to elute before more polar ones, hence the name normal phase chromatography.
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Why does chlorophyll b appear yellow green? How is polarity related to RF values? The stronger a compound is bound to the adsorbentthe slower it moves up the TLC plate. Non-polar compounds move up the plate most rapidly higher Rf valuewhereas polar substances travel up the TLC plate slowly or not at all lower Rf value.
Is chlorophyll b Polar? This makes chlorophyll b slightly more polar than chlorophyll a. After we isolate the pigment mixture from the leaves in a hexane solution, we will use the difference in polarity to separate the various pigments using column chromatography.What does a high RF value mean in paper chromatography? It is used in chromatography to quantify the amount of retardation of a sample in a stationary phase relative to a mobile phase.
See Full Answer.
What does it mean to have a high RF value? A high Rf Ie 0. A low Rf value 0. Retention time RT is a measure of the time taken for a solute to pass through a chromatography column. It is calculated as the time from injection to detection. The RT for a compound is not fixed as many factors can influence it even if the same GC and column are used. Rf values. The Rf value of a particular compound is always the same - if the chromatography has been carried out in the same way.
This allows industry to use chromatography to identify compounds in mixtures. What does a small RF value tell you? Beta carotene is carried the furthest because it is highly soluble in the solvent and because it forms no hydrogen bonds with the chromatography paper fibers. Chlorophylls are bound more tightly to the paper than the other two, so they travel the shortest distance.
Chemistry Stack Exchange is a question and answer site for scientists, academics, teachers, and students in the field of chemistry. It only takes a minute to sign up. Three eluents of varying polarity were used. Select the TLC plate that was developed using the least polar eluent click on the corresponding TLC number 1, 2, or 3 on the bottom of the plate. If this is the case then plate 3 has the least polar eluent because the compounds are at the top.
For the same reason compound Z would be the least polar. It also does not make sense theoretically. You must learn the terminology to follow along in chemistry. If in doubt Google the term Eluent - As Zhe noted "Eluent is a fancy name for solvent in chromatography.
For GC a gas is used. Normal phase TLC - For normal phase TLC the stationary phase is polar and the mobile phase is typically non-polar or only moderately polar.
Polar molecules are attracted to the stationary phase while non-polar compounds are carried along by the mobile phase. Reverse phase TLC - For reverse phase TLC the stationary phase is non-polar and the mobile phase is typically moderately polar to strongly polar. Non-polar molecules are attracted to the stationary phase while polar compounds are carried along by the mobile phase. The normal designations is because the first HPLC columns used alumina and silica packing, which are both polar, in columns.
With setup The least polar compounds were eluted first and the most polar compounds were eluted last. Switching to non-polar packing was then noted as reverse phase since it reversed the order of elution. The most polar compounds were eluted first and the least polar compounds were eluted last. So the problem would seem to be ambiguous.
We don't know that any of the solvents is "absolutely" non-polar like hexane, or that one might be "absolutely" polar like water. Sign up to join this community. The best answers are voted up and rise to the top. Home Questions Tags Users Unanswered.
How does the polarity of the eluent and sample affect the Rf value in thin layer chromatography? Ask Question. Asked 3 years, 1 month ago. Active 3 years, 1 month ago. Viewed 15k times. The term eluent means solvent doesn't it.
Jason Jason 31 1 1 gold badge 2 2 silver badges 6 6 bronze badges.During thin layer chromatography, a technician places spots of a chemical mixture on a flat plate coated with a layer of absorbent material, then sits the lower portion of the plate in solvent.
As solvent moves up the plate, chemicals in the mixture move up with it at different rates, so they separate. This test determines which chemicals are in a mixture by comparing the travel rates of unknowns to known standards.
The results, however, can be affected by many factors. Retention factor values in thin layer chromatography are affected by the absorbent, the solvent, the chromatography plate itself, application technique and the temperature of the solvent and plate. The retention factor for a chemical during thin layer chromatography is a measure of how far it moves up the plate in response to the solvent movement.
Since the absolute movement of the chemical depends on how far the solvent travels, you calculate retention factor values relative to the degree of solvent movement. The retention factor for a chemical is the vertical distance moved by the chemical from the spot where it was originally applied to the plate, divided by the distance traveled by the solvent — measured from the same starting point.
The thin layer chromatography plate itself can affect the retention factor value obtained for a given chemical. Thin layer chromatography plates can be coated with a variety of absorbent solids; most frequently silica or alumina. Since the retention factor is based on the relative affinity of the chemical for the absorbent compared to the solvent, changing the absorbent can greatly change the retention factor.
Also, the thickness and uniformity of the layer of absorbent can vary from plate to plate, especially if they are handmade. These factors can also change the retention factor value for chemicals.
Since the solvent carries the chemical up the plate, the particular solvent used will also have a substantial impact on the retention factor value for the chemical. A solvent which has a stronger interaction for a particular chemical will more easily overcome any affinity of the chemical for the absorbent layer, and move that chemical farther in a given period of time. Mixtures of solvents can also have different effects depending on the proportion of each solvent.
There are a few other factors which may affect the retention factor in some cases. The temperature of the solvent and plate may make slight changes, since, for example, the solvent can often better dissolve the chemicals it is transporting at higher temperatures. The technique of the technician in applying the sample to the plate may also change the retention factor.
Applying too much sample may result in large, diffuse bands of chemical moving up the plate, making it difficult to accurately measure the distance the chemical has been transported. Michael Judge has been writing for over a decade and has been published in "The Globe and Mail" Canada's national newspaper and the U. Michael has worked for an aerospace firm where he was in charge of rocket propellant formulation and is now a college instructor. TL;DR Too Long; Didn't Read Retention factor values in thin layer chromatography are affected by the absorbent, the solvent, the chromatography plate itself, application technique and the temperature of the solvent and plate.
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