This is 3 graph of azo dye in acidic, basic, and neutral condition. First I woul

Question

This is 3 graph of azo dye in acidic, basic, and neutral condition. First I would like to know which one is acidic, which one is basic, and which one is neutral? Second, I need an analyze of peaks for all 3 graphs and their relationship? This is 3 graph of azo dye in acidic, basic, and neutral condition. First I would like to know which one is acidic, which one is basic, and which one is neutral? Second, I need an analyze of peaks for all 3 graphs and their relationship? 1.5 515 95nm, 125A So, H 1.4 305 13m, 1.3 31.97mm, 1.13A 1.2 1.1 1.0 0.9 520 0.8 0.7 0 6 05 0.4 03 0 2 300 400 500 nm 600 700 Name Description Sampe390 Sample Sample391 Sample Sample392 Sample

Explanation / Answer

Identification of obtained absorption peaks of the azo dye according to pH change- (If we see from left hand side to right hand side of the graphs)-

In acidic medium = 515.95 nm

In neutral medium = 520.00 nm and

In basic medium = 531.97 nm

Now description to analyze of peaks for all 3 graphs and their relationship:

If we see the reactants, the formed azo dye molecule would contain -SO3H, -NH2, -OH and -NO2 functional groups directly attached to aromatic rings. change in graphs can be easily corelated with electrone density of pi-conjugated system in azo dye. If the energy difference of highest occupied moleculat orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) is higher then obtained absorption peak will be at lower wavelength (nm, x-axid) region. and vice-versa.

In acidic condition H+ ion will effect mostly the -NH2 group with formation of -NH3+, so the lone pair (present on N-atom) contribution to the aromatic ring will be decreased. Ultimately electrone density in the conjugated pi-sytem will be decreased and HOMO-LUMO energy difference will be increased. energy increased means wavelength decreased so the value is 515.95 nm.

No we can easily say about neutral condition. where this effect will not be observed. and the peak will come at higher level. =520.00 nm

In basic condition, due to presence of OH- ions, these will effect mostly -OH group. here this -OH is a phenolic group and the H-atom is very acidic so it (H-atom) will be removed by acid base reaction and phenoxide stable ion will be formed which increases electron density in the pi-conjugated system and decreases HOMO-LUMO gap. so wavelenth increases to 531.97 nm.

Remind that energy and wavelength are inversely proportional.

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