Assigned is Nitrite. As in previous experiments, review experiment 1, colorimetr

Question

Assigned is Nitrite.

As in previous experiments, review experiment 1, colorimetry will be used to determine the concentration of nitrogen (ammonia, nitrite, nitrate) or phosphorus (phosphate) in your water samples as indicated below. Ammonia will not be measured due to the imitation and availability of the chemicals needed Beer- Lambert Law - Remember from previous experiments that absorbance is directly related to the concentration of solute according to the following equation: A = epsilon bc = -log(I/I_D) Epsilon, epsilon, is the molar absorptivity, b is the cuvette width and c is the concentration of solute. A graph of A versus c yields a straight line. You will be assigned a form of nitrogen and the concentration of a standard solution for your form of nitrogen. ft is imperative that you prepare and complete the table in this prelab assignment before you come to the lab. For the assigned nitrogen ion under study prepare a table that will contain 8 standard dilutions from a standard solution. Remember that for dilutions we can use M_1V_1 = M_2V_2. Your TA needs to review and approve your calculations prior to performing the experiment. Form of Nitrogen to Study: ___ Concentration of Standard: ___

Explanation / Answer

If the assigned ion is nitrite then diazotization reaction of aniline (with strong acid) is conducted followed by azo coupling by adding a coupling agent like aniline.

Diazotization-

Ar-NH2 +NO2-+H+X------>Ar-N2+X-(diazonium salt)

coupling

Ar-N2+X-+ArNH2 ---->Ar-N2+-Ar-NH2(intensely colored) yellow azo dye(precipitate)

Ar-N2+X-+Ar-OH ---->Ar-N2+-Ar-OH(intensely colored) orange azo dye (precipitate)

known standard solutions of nitrite ions are diazotized with known amount of aniline and then coupled with known amount of aniline/phenol. The dye is precipitated,to be washed, vaccuum filtered ,separated and dissolved in suitable solvent (water )

The compound formed is intensely colored and absorbs longer wavelength.The absorbance of the standard solutions are measured and a callibration curve between concentration of nitrite and absorbance is to be plotted.

A=ebc (beer's law ) so Absorbance is directly proportional to concentration of ions

next for the unknown nitrite sample,absorbance is measured and concentration determined from the callibration curve(abscissa corresponding to the absorbance(ordinate))

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