How do you calculate Rf values GCSE?

Asked By: Narjiss Varez | Last Updated: 18th February, 2020
Category: science chemistry
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Keeping this in view, what are the RF values?

RF value (in chromatography) The distance travelled by a given component divided by the distance travelled by the solvent front. For a given system at a known temperature, it is a characteristic of the component and can be used to identify components.

Also, what is RF calculation? 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.

Beside above, how are RF values useful?

The farther a compound travelled, the larger it's Rf value. You can use this technique to compare all sorts of compounds in a lab. You can also identify or narrow down compounds by spotting a known compound, and looking to see which of your unknown compounds have the same Rf value as your known test spot.

What is a good RF value?

By definition, Rf values are always less than 1. 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. Another run must be made using a less polar solvent to improve the separation.

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What does 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. A low Rf value (0.10) would refer to a substance that is very polar.

What does Rf value tell you about purity?

However, because Rf values are relative, not absolute, some compounds may have very similar Rf values. A mixed melting point measurement is needed to unambiguously identify the unknown compound. It is primarily used to determine the purity of a compound. A pure solid will show only one spot on a developed TLC plate.

How does Rf value relate to polarity?

In general, the adsorptivity of compounds increases with increased polarity (i.e. the more polar the compound then the stronger it binds to the adsorbent). 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).

What does RF mean?

radio frequency

What is the RF value of amino acid?


Chromatography of amino acids
Amino acid Rf value
leucine 0.73
lysine 0.14
methionine 0.55
phenylalanine 0.68

Why silica gel is used in TLC?

Silica gel is by far the most widely used adsorbent and remains the dominant stationary phase for TLC. The surface of silica gel with the highest concentration of geminal and associated silanols is favored most for the chromatography of basic compounds because these silanols are less acidic.

What is an Rf value in TLC?

The Rf value (for TLC) is simply the (migration distance of substance)/(migration distance of solvent front). The Rf value is often used, along with other evidence, to help identify a compound when compared with a known standard.

Can two compounds have the same Rf value?

“Relative Rf” means that the values are reported relative to a standard, or it means that you compare the Rf values of compounds run on the same plate at the same time. If two substances have the same Rf value, they are likely (but not necessarily) the same compound.

What does an RF value of 0 mean?


The highest Rf value is 1, which, by definition, means at the very top of the plate. The lowest Rf value is 0, which again, by definition, means at the very bottom of the plate. Rf values have nothing to do with polar or nonpolar, it is just another way of measuring the distance from the bottom of the plate.

What is the relationship between structure and RF value?

It is a measure of how strongly the substituents are attached (adsorp) to the stationary phase. The stronger the adsorption, the lower is the Rf value. By the way, Rf can be calculated by dividing the distance covered by the substituent with distance covered by the mobile phase.

Is a higher Rf value better?

The stronger a compound is bound to the adsorbent , the slower it moves up the TLC plate. 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).

How is RF value used in identifying unknown compound?

R f values can be used to identify unknown chemicals if they can be compared to a range of reference substances. The Rf value for a particular substance is always the same if the same solvent and stationary phase are used.

Why do amino acids have different RF values?

The different amino acids move at differing rates on the paper because of differences in their R groups. The rate of movement of a biomolecule during paper chromatography is reported as its relative mobility (Rf).

Which pigment has the lowest RF value?


Explanation
Pigment Rf value
β-carotene 0.98
Chlorophyll a 0.59
Chlorophyll b 0.42
Anthocyanins 0.32-0.62

What are RF values for plant pigments?

Rf = (distance moved by pigment)/ (distance moved by solvent)
  • Rf for carotenes = 9.7cm/9.8cm = 0.99.
  • Rf for xanthophylls = 7.2cm/9.8cm = 0.73.
  • Rf for chlorophyll a = 5.1cm/9.8cm = 0.52.
  • Rf for chlorophyll b = 3.7cm/9.8cm = 0.38.

What is the basic principle of chromatography?

Chromatography is based on the principle where molecules in mixture applied onto the surface or into the solid, and fluid stationary phase (stable phase) is separating from each other while moving with the aid of a mobile phase.