Investigation of the Beer - Lab Report Example

Scientists rely on physical and chemical properties when describing chemical properties. Physical and chemical properties can be used quantitatively to determine the presence of material in a solution, or qualitatively to predict the behavior of a solution. In this lab, we developed a scheme to investigate the validity of Beer-Lambert law. In order for compounds to have color, they must absorb light. Chemicals with metal ions exhibit a wide range of colors. For a compound to have color, visible light must be absorbed.

Visible light contains electromagnetic radiations of wavelengths ranging between 400nm and 700nm. It illustrated in the diagram below. Beer-Lambert law states that the absorbance is directly proportional to the concentration of the solution. It relates the absorbance of sample (A) to the concentration of the substance in the solution absorbing it and the path length of the light.Incident light from a tungsten or deuterium lamp is focused through a lens and passed through a slit. Passing the beam through the wavelength selector diffracts it separating it into the light of a single wavelength.

This particular wavelength is selected and exits through the slit. The light passing through the sample is detected by the photodetector which then converts it into an electrical current measured by the galvanometer. The reading is then sent to a read-out device.The plot of absorbance of light at different wavelengths is called its absorption spectrum. Fig. 1 gives the absorption spectrum of potassium permanganate (KMnO4 ). According to Beer-Lambert law, absorbance is directly proportional to concentration.

This is clearly illustrated in Fig. 4. This is also known as a calibration curve. It should be drawn with the utmost accuracy in order to obtain a straight line graph. The slope of this curve is equal to the absorbance of the potassium permanganate (Skoog, 45).One source of error is the use of inappropriate concentrations when applying Beer-Lambert law. It is only applicable for dilute solutions and becomes less accurate with an increase in concentration. Another source of error is stray light or scattering within the instrument as this causes large errors, especially when reading small values.

The aim of the experiment was obtained because the Beer-Lambert law was verified. Using linear regression analysis, Beer-Lambert law (A = εlc) implies that when concentration is equal to zero, absorbance must also be zero. This is a straight line equation passing through the origin hence the aim was achieved. Absorbance is directly proportional to the concentration and path length. Beer-Lamberts law is also a straight line equation when linear regression analysis is applied.