# How is Rf value calculated?

## 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.

## How do you calculate Rf in paper chromatography?

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.

## 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 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.

## Are Rf values ratios?

Rf values are ratios. An Rf value is the ratio of the distance moved by the compound as compared to the distance moved by the solvent. If the solvent only moves a short distance, then the Rf value will be small.

## What does Rf stand for 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.

## How do you find the Rf value of an amino acid?

The Rf value can be calculated by measuring the distance of the substance from its starting point in millimeters, as well as the distance the solvent traveled from its starting point in millimeters, then dividing the substance distance by the solvent distance.

## How does Rf value relate to polarity?

In general, low polarity compounds have higher Rf values than higher polarity compounds. 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). The eluting power of solvents increases with polarity.

## What is Rf value used for in chromatography?

Rf values in chromatography are the basic requirement of the whole experiment. These values tell us whether the analyte (solute) is more affinitive with stationary or the mobile phase. Rf values evaluate the polarity, relative masses, and relative solubilities with stationary and mobile phases, etc.

## 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 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 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.

## 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.

## What is chromatography GCSE?

Paper chromatography is used to separate mixtures of soluble substances. These are often coloured substances such as food colourings, inks, dyes or plant pigments.

## How do you calculate the Rf of a protein?

The Rf is defined as the migration distance of the protein through the gel divided by the migration distance of the dye front. The distance should be measured from the top of the resolving gel to the band of interest, as illustrated on the gel.

## How do you calculate retardation factor?

Define Retardation Factor It is the ratio of the time that a substance spends in the stationary phase to the time that it spends in the mobile phase. Therefore in Rf= Ds/Df ,where RF is the retardation factor, Ds is the migration distance of the substance and Df is the migration distance of the solvent front.

## Why amino acids have different Rf values?

Why do amino acids have different Rf values? Different amino acids have different Rf values because their R groups are chemically different; this gives each amino acid its own unique solubility in the developing solvent and, therefore, its own unique migration distance.

## How do you calculate the polarity index 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.

## Why is Rf less than 1?

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. This happens when the eluting solvent is too polar for the sample.

## Can two compounds have the same Rf value?

If two substances have the same Rf value, they are likely (but not necessarily) the same compound. If they have different Rf values, they are definitely different compounds.

## Are Rf values constant?

The symbol Rf stands for “retardation factor” or “ratio-to-front”. It is expressed as a decimal fraction. When the conditions are duplicated, the same average relative positions will turn up for the solvent and solute; thus the Rf value is a constant for a given compound.