| why a solution, such as Giemsa staining solution, appears colored | it absorbs certain wavelengths of light in the visible spectrum and transmits or reflects others. |
| Do Each solution with a different solute has its own characteristic absorption properties or spectrum. | yess |
| spectrophotometer | an optical machine that measures how much light energy is transmitted by a substance in solution at different wavelengths of radiant energy. |
| spectrophotometer for two different purposes are | To determine the absorption spectrum of a pure substance in solution and
To determine the concentration of a solution. |
| A spectrophotometer consists of a what | white light source (light of all visible wavelengths), a prism or diffraction , a slit , a sample solution holder, a photosensitive tube, and a recording device |
| what is transmittance | is the ratio of the transmitted light energy (I) to the incident light energy (I0). |
| I transmittance proportional to the solute concentrate and why/why not | is not proportional to the solute concentration, so it is usually converted into absorbance which is proportional to the solute concentration. |
| chlorophylls in plants absorb how much and which colors | strongly in the blue wavelengths (about 450 nm) and red wavelengths (about 650 nm), but reflect the green wavelengths (about 525 nm). |
| A plot of absorbance versus visible wavelengths (400 to 700 nm) for a solution of chlorophyll a shows two major peaks | one at 450 and one at 650 nm, and a valley from 500 to 625 nm. |
| how can we find or measure absorption spectrum of a sample. | By measuring the absorbance of an uncharacterized solution over a range of wavelengths and plotting the absorbance value on the y-axis and the wavelength on the x-axis |
| The absorption maximum of any pure substance in the solution is best in what | suitable wavelength for determination of its concentration. |
| Spectrophotometry can be used to measure | the absolute or relative concentration of a characterized substance in solution. |
| how To determine the absolute concentration of a pure substance | one must construct a standard concentration curve from known concentrations and then take the absorbance reading of the unknown concentration. |
| how A standard concentration curve of a solution is constructed | by measuring the absorbance of several different known concentrations of the solution at absorption maximum and graphing the results by plotting absorbance on the y-axis and concentration on the x-axis. |
| how The unknown concentration can be determined | 1. from the standard curve by drawing a horizontal line on the graph parallel to the x-axis and through the point on the y-axis which corresponds to the absorbance.
2. This line will intersect the standard curve; at this intersection, a vertical line is dropped to the x-axis and the concentration read from the x-axis.
3. Two factors are important in determining unknown or relative concentrations.
4. The absorption maximum should be used, and absorbance rather than percent transmittance should be plotted because absorbance is directly proportional to concentration and transmittance is not. |
| what is prism or diffraction grating | that separates the light into different wavelengths |
| a slit | through which a narrow beam of the desired wavelength passes (the incident light, I0) |
| a photosensitive tube | which measures the energy of light transmitted through the solution (I) |
| a recording device | displays the amount of transmitted light energy digitally or on a dial. |
