Question

Colorimetry:
-Definition
-Principle
-Theories
-Instrument used
-Advantages
-Disadvantages

Answer 1

Colorimetry is a technique used to determine the concentration of coloured substance in a sample.

It is based on the principle of Beer's Lambert law which state concentration of coloured substance in a sample is directly proportional to the absorbance. Intensity of colour is directly proportional to it's concentration.

In colorimeter, a beam of light with specific wavelength is passed through the solution and solution absorbs light of particular wavelength and colour of transmitted light is complementary to the absorbed light. The colour of transmitted light is then compared with incident light from which we get wavelength of absorbed light. In colorimetry, entire visible spectrum is used that is from 400nm to 750nm.

There are three components of colorimetry are a light source, a cuvette containing the solution and a photocell to detect the light transmitted by the solution. The output of colorimeter is displayed on digital meter in terms of transmittance or absorbance. If a monochromatic light or narrow band of radiation is used then instrument is called spectrophotometer.

Application : Colorimeter is used in biochemical investigation that involves quantitative estimation of colour. Most of chemical compounds are determined colorimetrically. A small concentration of sample can also be used. Colorimetry is also used to monitor the growth of yeast and bacterial cell. It also found application in testing water quality by screening chemicals. It is used in colour printing, textile manufacturing and paint manufacturing. They are also used to determine the concentration of haemoglobin in blood.

Advantages: Inexpensive, easy to monitor, small amount of sample required, good quality result.

Disadvantages : Voltage fluctuations may cause error.

Sometime impurities also absorbs same radiations which give error.

Can't be used for colourless substance

It works only in visible region.