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Computer-Interfaced Experiments - Absorption Measurement Positive Solvatochromism Objectives: Shift of the Spectrum, Solvent Polarity Peter Keusch |

Hazards and safety precautions:
Safety glasses and gloves must be worn. The preparation of the corresponding solutions and the experimental procedure are carried out in a fume hood! Experimental procedure: Spectronic 20 (Download) features an analog output on the bottom of the instrument. The analog output of the photometer is connected to the input B of the INTERFACE. The photometer has been designed so that when it displays 100 % transmittance, the analog signal at its output connector is 1 VDC; when the instrument displays 0 % transmittance, the output voltage is 0 VDC. Matching of the program 'Multimeter': - In the program 'Measuring and Evaluating' the subprogram 'Multimeter' is activated and via the menu item <F3> 'Select measur. quantities' ®'Reselect channel B' the quantity 'Voltage DC'is selected. - After the program has been switched to <F4>'Automatic/Param./Select formula'® Enter parameter wavelength is entered. Also l and nm are entered. l stands for 'Physical symbol' and nm for 'Physical unit'. - Under the menu item 'Enter formula' A is entered. A stands for 'Physical symbol' . The 'No. decimal places ' is set to 4 . According to A = 2 - logU · 100 the beginning of the formula A (n, l, U) = is completed by entering - lnU / ln10 (Fig. 1) ![]() Fig. 1: Menu screen - Matching of the program |
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| Solvent | Color of the solution | Absorption maxima
| methanol
| purple |
555 nm / 365 nm
| acetone
| red
| 500 nm / 470 nm
| toluene
| orange
| 485 nm / 445 nm | |

