What is colorimetry used to determine?

The concentration of a coloured substance in solution by measuring absorbance or transmission of light and comparing to a calibration curve.

How is a calibration curve prepared for colorimetry?

By preparing solutions of known concentrations, measuring their absorbance or transmission, and plotting the values.

How is the concentration of an unknown sample determined using colorimetry?

Measure the absorbance of the unknown sample and read the corresponding concentration from the calibration curve.

What is the basis of separation in thin layer chromatography?

Molecules are separated based on their relative solubility in the mobile phase solvent and their adsorption to the thin layer of silica or alumina on the plate.

State the formula for calculating Rf value.

Rf = distance moved by solute ÷ distance moved by solvent front.

OCR A-Level Biology H420

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Biological Molecules

Colorimetry and chromatography

1 thing to know
Components 01, 02 and 03

Overview

Using a calibration curve to find an unknown concentration, and separating molecules by paper and thin layer chromatography with the Rf calculation.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

What is the basis of separation in paper chromatography?

Questions from this subtopic

Each one with the model answer underneath.

1
What is colorimetry used to determine?
Model answer
The concentration of a coloured substance in solution by measuring absorbance or transmission of light and comparing to a calibration curve.
2
How is a calibration curve prepared for colorimetry?
Model answer
By preparing solutions of known concentrations, measuring their absorbance or transmission, and plotting the values.
3
How is the concentration of an unknown sample determined using colorimetry?
Model answer
Measure the absorbance of the unknown sample and read the corresponding concentration from the calibration curve.
4
What is the basis of separation in paper chromatography?
Model answer
Molecules are separated based on their relative solubility in the mobile phase solvent and their adsorption to the stationary phase paper.
5
What is the basis of separation in thin layer chromatography?
Model answer
Molecules are separated based on their relative solubility in the mobile phase solvent and their adsorption to the thin layer of silica or alumina on the plate.
6
State the formula for calculating Rf value.
Model answer
Rf = distance moved by solute ÷ distance moved by solvent front.

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AA phospholipid contains one glycerol molecule.

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