# How do you calculate Rf values in chromatography paper?

To calculate an Rf value, divide the distance travelled by the component – in other words, the distance from the starting pencil line to the coloured spot -by the distance travelled by the solvent. Rf values are important because each component has a fixed Rf value under a specific set of conditions.

## What is the formula to calculate Rf value?

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 is Rf value in chemistry?

What is RF Value? The Rf (retardation factor) value is the ratio of the solute’s distance travelled to the solvent’s distance travelled. The word comes from chromatography when it was discovered that a given component will always travel the same distance in a given solvent under the same conditions.

## Why do we calculate Rf values?

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.

## What 2 distances are important when calculating Rf values in chromatography?

By definition, the Rf value is taken as the distance from the centre of te zone. This is however prone to visual estimation errors, so the best way to calculate the centre is to measure the following 2 distances: measurment from origin to the top edge of the zone, measurment from origin to the bottom edge of the zone.

## How does Rf value relate to polarity?

The fastest moving spot has the highest Rf value. polar (fastest moving), and the spot with the lowest Rf value is the most polar (slowest moving). Rf values are frequently used to compare a known and an unknown substance to determine if they are the same.

## How do you calculate molecular weight from Rf values?

Use a graphing program, plot the log (MW) as a function of Rf. Generate the equation y = mx + b, and solve for y to determine the MW of the unknown protein. Run the standards and samples on an SDS-PAGE gel. Process the gel with the desired stain and then destain to visualize the protein bands.

## What is the Rf factor in chromatography?

(2) Retardation factor (Rf) in chromatographic separation, is the ratio of the distance travelled by the substance of interest to the distance simultaneously travelled by the mobile phase: always less than 1.

## Can Rf value be greater 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.

## Why do different compounds have different Rf values GCSE?

The substances will move at different rates depending on how soluble they are in the solvent, and how attracted they are to the paper.

## What is the Rf value in TLC?

TLC plates: glass plates coated with silica gel that is impregnated with a fluorescent dye (use a 254 nm UV lamp for detection of the spots). By definition, Rf values are between 0 and 1.0. Best resolution is achieved in the Rf 0.3 – 0.7 range.

## What factors affect Rf values in paper chromatography?

• The solvent system.
• Composition of the mobile phase.
• The working temperature of the system.
• The quality of the paper used.
• The distance through which the solvent runs.
• The quality and nature of solvents used.
• The polarity of components.
• The pH of the solvent or mobile phase.

## What does Rf value stand for?

Calculating the Rf value The Rf (retardation factor) value is the ratio of the distance moved by the solute to the distance moved by the solvent.

## On what factors does the Rf value of a compound depend?

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.

## Do nonpolar compounds have higher Rf?

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 do you determine the polarity of a solvent?

One way you could actually calculate a solvent’s polarity is by using its dielectrict constant, which is used to measure how well the solvent can partly cancel the field strenght of the electric field of a particle added to it. The higher the value of a solvent’s dielectric constant, the more polar it will be.

## What is the relationship between Rf value and molecular weight?

A linear relationship exists between the logarithm of the molecular weight of native nucleic acid, and its Rf. The Rf is calculated as the ratio of the distance migrated by the molecule to that migrated by a marker dye-front.

## How do I calculate molecular weight?

Sample Molecular Weight Calculation Using the periodic table of the elements to find atomic weights, we find that hydrogen has an atomic weight of 1, and oxygen’s is 16. In order to calculate the molecular weight of one water molecule, we add the contributions from each atom; that is, 2(1) + 1(16) = 18 grams/mole.

## How do you calculate Rf for pigments?

1. Rf for carotenes = 9.7cm/9.8cm = 0.99.
2. Rf for xanthophylls = 7.2cm/9.8cm = 0.73.
3. Rf for chlorophyll a = 5.1cm/9.8cm = 0.52.
4. Rf for chlorophyll b = 3.7cm/9.8cm = 0.38.

## What is the relationship between Rf value and solubility?

The Rf values indicate how soluble the particular pigment is in the solvent by how high the pigment moves on the paper. Two pigments with the same Rf value are likely to be identical molecules. Small Rf values tend to indicate larger, less soluble pigments while the highly soluble pigments have an Rf value near to one.