Which pure product salicylic acid or acetylsalicylic acid should have the higher RF value Why?
Which pure product salicylic acid or acetylsalicylic acid should have the higher RF value Why?
Due to higher interaction among molecules, salicylic acid is less attracted to the stationary phase and will move further up the plate thus having a higher Rf value than the standard salicylic acid and a closer Rf value to the acetylsalicylic acid in the reaction mixture.
What is the RF value of ibuprofen?
~0.56
What is Rf value?
In thin-layer chromatography, the retention factor (Rf) is used to compare and help identify compounds. The Rf value of a compound is equal to the distance traveled by the compound divided by the distance traveled by the solvent front (both measured from the origin).
What does a high RF value mean?
Definition. Rf = distance traveled by substance/distance traveled by solvent front. A high Rf (Ie 0.92) would refer to a substance that is very non-polar. Ie that substance moved a 92% of the entire distance the solvent traveled. The farther a compound travelled, the larger it’s Rf value.
What are good RF values?
The best Rf (retention or retardation factor) lies between 0.3 and 0.7. If you want the Rf of your TLC spot to be smaller, i.e., the spot to be lower down on the plate, you must decrease the eluent polarity.
Why is a high RF value bad?
An Rf value of 1 or too close to it means that the spot and the solvent front travel close together and is therefore unreliable. This happens when the eluting solvent is too polar for the sample. Another run must be made using a less polar solvent to improve the separation.
Why is RF value important?
Rf value stands for the retardation factor value. It tells us how far the unknown pigment traveled in relation to the distance the solvent traveled. The Rf value is useful for scientists because it allows scientists to identify the pigment by comparing its Rf value to that of a known standard.
What affects Rf value?
Retention Factor Rf values and reproducibility can be affected by a number of different factors such as layer thickness, moisture on the TLC plate, vessel saturation, temperature, depth of mobile phase, nature of the TLC plate, sample size, and solvent parameters. These effects normally cause an increase in Rf values.
Does higher RF mean more polar?
The eluting power of solvents increases with polarity. Non-polar compounds move up the plate most rapidly (higher Rf value), whereas polar substances travel up the TLC plate slowly or not at all (lower Rf value).
Why are RF values less than 1?
Rf is a fraction. It is the ratio of how far a substance travels up the chromatography paper compared to the distance the solvent has travelled. This means that it must be less than 1.
Can an RF be greater than 1?
Since the pigment is carried by the solvent an Rfgreater than one is not possible. The molecular size of the pigment is inversely proportional to the Rf value.
What does an RF value of 0 mean?
The distance a particular molecule, or spot, travels relative to the distance travelled by the eluting solvent is called the Rf value. The Rf value ranges from 0 (indicating the molecule did not move up the plate at all) to 1 (indicating the molecule traveled all the way up the plate).
Why Rf value has no units?
Rf values do not have units since it is a ration of distances. Because mixture solvents are often applied Rf values are usually written as the following examples: Rf = 0.66 (60% Ethanol) – if % is given it is assumed that the mixture is in water hence 60% ethanol 40% water.
What does Rf value tell you about purity?
It is primarily used to determine the purity of a compound. A pure solid will show only one spot on a developed TLC plate. The Rf values indicate how soluble the particular pigment is in the solvent by how high the pigment moves on the paper. A high Rf (Ie 0.92) would refer to a substance that is very non-polar.
What are the RF values of pigments?
| Pigment | Rf value range | Relative position |
|---|---|---|
| Pheophytin b | 0.33-0.40 | Below the top yellow, above the greens |
| Chlorophyll a | 0.24-0.30 | Above the other green, below the grey |
| Chlorophyll b | 0.20-0.26 | Below the other green |
| Xanthophylls | 0.04-0.28 | Below, or almost at the same level of, the highest green |
What is the maximum RF value for any compound in paper chromatography?
Size of spot may range 2-5 mm depending upon number of sample to be applied to the paper. The mobile phase which gives Rf value range between 0.2-0.8 are selected for chromatographic work.
Which compound has the highest RF value?
Rf value is equal to the distance traveled by the solvent divided by the distance traveled by the compound on the TLC plate. Rank the following molecules from 1-4 with respect to their Rf values on a TLC plate developed in 60:40 ethyl acetate:hexane, where a 1 is the lowest Rf value and 4 is the highest Rf value.
Why do we use pencil in chromatography?
Pencil is always used to mark chromatography paper or TLC plates because ink may run and interfere with the chromatogram. As soon as the paper/plate is taken out, mark the solvent front with a pencil before the solvent evaporates and the front becomes impossible to see.
Why are two solvents used in chromatography?
Why are two solvents used in the process? Different pigments will be soluble in one solvent but not another.
What is the best solvent for chromatography?
Readily Available Solvents for Paper Chromatography
| Solvent | Polarity (arbitrary scale of 1-5) | Suitability |
|---|---|---|
| Water | 1 – Most polar | Good |
| Rubbing alcohol (ethyl type) or denatured alcohol | 2 – High polarity | Good |
| Rubbing alcohol (isopropyl type) | 3 – Medium polarity | Good |
| Vinegar | 3 – Medium polarity | Good |
Why water is not used in paper chromatography?
The stationary phase of paper chromatography is cellulose paper which polar and water are also quite polar, therefore there is no distinction by which to separate the molecules. The water is not used in the paper chromatography, due to the water the paper swells up and ultimately dissolves.
Why is acetone a better solvent than water?
Acetone is a good solvent due to its ability to dissolve both polar and nonpolar substances, while other solvents can only dissolve one or the other. Secondly, acetone is a good solvent because it is miscible substance, meaning it has the ability to mix with water in all proportions.
Why is acetone a bad solvent for chromatography?
Acetone is less desirable to use because it has high volatility, often making it difficult to pump. Also, it is not usually available in HPLC grade, which could result in contamination of the system.
Why do we use acetone in chromatography?
Its slight polarity allows it to dissolve polar substances, and the fact that it is less polar than waterallows greater resolution between pigments on paper. These reasons allow acetone to be a greatsolvent for pigment chromatography.
Why is it important to use a good solvent for paper chromatography?
When performing chromatography, it is necessary to find a solvent that will dissolve the pigment in question. Water can dissolve polar solvents, but it is very poor at dissolving polar solvents. The further up the paper a solvent can travel, the greater amount of resolution can be achieved.
What is the function of solvent?
What is a solvent? The term ‘solvent’ is applied to a large number of chemical substances which are used to dissolve or dilute other substances or materials. They are usually organic liquids. Many solvents are also used as chemical intermediates, fuels, and as components of a wide range of products.
Why do we use acetone to extract chlorophyll?
Acetone breaks down chlorophyll’s lipid bonds to a plant’s thylakoid structure and suspends the pigment in solution. Acetone is the standard solvent for chlorophyll extraction, but ethanol, methanol, propanol, petroleum and N-dimethylformamide can also fulfill this role.