[Chemistry Class Notes] on Colorimeter Pdf for Exam

A Colorimeter is a light and sensitive device used to measure the transmittance and absorbance of light that passes through a liquid sample. The colorimeter device also measures the intensity or colour concentration that develops upon introducing a particular reagent into a solution.

Types of Colorimeter

Colour densitometers, which measures the density of primary colours, Colour photometers, which measures transmission and colour reflection. Usually, the Colorimeter is used to measure the known solute concentration in a given solution with the help of Beer-Lambert law. The Colorimeter was invented by Louis J Duboscq, in the year 1870.

Principle of Colorimeter

Let us discuss the principle of colorimeters. 

A photometric is a technique that states that when a beam of incident light of intensity Io passes through a solution, it occurs the following.

• A part is reflected which is denoted as Ir

• A part is absorbed which is denoted as Ia

• The remaining light is transmitted, which is denoted as It
  Thus, Io = Ia+ Ir +It
  To determine  IaThe measurement of It and Io is sufficient. Therefore, Ir is eliminated and the amount of light reflected is kept constant to measure It and Io.
  The Colorimeter is based on two fundamental photometry laws. Let us discuss them briefly.

This law states that the amount of light absorbed is always proportional to the solute concentration present in the solution.

Log10 Io/It = asC

Where “C” is the concentration of the solution, and “as” is the absorbency index.

A = log10 Io/It = asb

where, “as” is the standard absorbance and “A” is the test absorbance of the test, and “b” is the thickness/length of the solution.

Working of Colorimeter

As discussed in the Colorimeter’s different principles, let us look at the working of the colorimeter.

Before going to start the experiment, it is essential to calibrate the Colorimeter. It can be done with the help of the standard solutions of the known solute concentration that has to be determined. Then, fill the standard solutions in the cuvettes and place them in the cuvette holder of the Colorimeter.

A light ray of a particular wavelength specific to the sample is in the direction of the solution. The light travels through a series of various filters and lenses. The coloured light then navigates by taking the help of lenses, and the filter allows the split of a beam of light into different wavelengths allowing only the required wavelength to pass through and reach the standard test cuvette.

As the light beam reaches the cuvette, it is transmitted, reflected, and absorbed by the solution. The transmitted ray falls on the photodetector system, where the intensity of transmitted light is measured. Now, the photodetector system converts the beam into electrical signals and sends it to the galvanometer.

The electrical signals that are measured by the galvanometer display in digital form.

Formula to determine the substance concentration in the test solution is,

A = ∈cl

Where “∈” and “l” are constants for the standard and test solutions, 

AT = CT —- (i)

AS = CS —- (ii)

From the above two equations, we get the colorimeter formula as,

AT × CS = AS × CT

CT = (AT/AS) × CT

Where “AT” is the optical density/absorbance of the test solution, 

“AS” is the absorbance / optical density of the standard solution, 

“CT” is the concentration of the test solution, and 

“CS” is the standard concentration.

Colorimeter Uses

Let us look at some uses of the colorimeter. We use a Colorimeter device to test the water quality by screening chemicals such as chlorine, cyanide, fluoride, dissolved oxygen, iron, zinc, hydrazine, and molybdenum. It is used in hospitals and medical laboratories to estimate biochemical samples, including plasma, urine, cerebrospinal fluid, serum, and a few more.

Besides, it helps in the identification of counterfeit and substandard drugs. Most of the food industries use this device. Paints and textile manufacturers use a colorimeter. This device often checks the strength and durability of the colours in paints and fabrics to ensure a similar quality.

Colorimeter Applications

Few of the applications of colorimeters are explained here. 

• Colorimeters are widely used to monitor bacterial growth or yeast culture. 

• They provide highly accurate and reliable results when used for the assessment of colour in bird plumage. 

• They are also used to monitor and measure the colour of various foods and beverages, including sugar and vegetable products. Certain colorimeters can even measure the colours used in fax machines, copy machines, and printers.

• A colorimeter is used for basic research in chemistry laboratories, in addition, colorimeters have numerous practical applications including testing water quality by screening chemicals such as fluoride, zinc, chlorine, cyanide, iron, dissolved oxygen, molybdenum, and hydrazine. 

•  Also, they are used to determine the plant nutrient concentrations such as nitrate, ammonia, and phosphorus in soil or the haemoglobin in the blood.

• Besides, Colorimetry is a process used in textile manufacturing, colour printing, and paint manufacturing for precise quality inspection.
  

Things to Take Care Before Using Colorimeter

The calorimeter, as said earlier,  is such a useful tool to determine the measure of the coloured substance in a solution. Therefore it must be handled with proper care and maintained consistently in order to make it free from any kind of dirt or damage. 

Some of the things that you can look into for taking care of a colorimeter are:

• Users should always remove the cuvette from the instrument when not using it.

• If any optical marks are found on the cuvette, gently clean it with tissue paper.

• Switch off the colourimeter when not in use. This will help the lamp to have a much more lasting life and will also save energy.

• After the work is done, it is preferred to disconnect the plug from the switchboard and cover the colorimeter with its’ protection cover.  

• Make it a habit to always check the main power adapter and cable to know if there is any wear or tear. Prolonged use of the colorimeter instrument with even the slightest wear and tear can not only damage the machine but is also dangerous. 

• Replace if the instrument is damaged.

• Always keep it in cool places and at room temperature.

• Do not keep it near harmful chemicals or burning materials. 

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