The U.V.-Enhanced Decomposition of Ammonium Nitrite

A solution of ammonium nitrite is usually obtained by mixing equimolar solutions of ammonium chloride and sodium nitrite since the solid is not thermally stable. On heating the mixed solution, it decomposes to water and nitrogen. The kinetics of the thermal decomposition can be readily followed by measuring at intervals the volume of nitrogen evolved from a thermostatted solution. Since a solution of ammonium nitrite exhibits absorption peaks in the u.v., it is likely that u.v. irradiation may increase the rate of gas evolution i.e. the rate of decomposition. 

Prepare a stock solution which is 0.4 M in ammonium and 0.4 M in nitrite ions. Fill a 2 mm spectrophotometer cell and record the spectrum over the range 250-390 nm. Dilute an aliquot 10-fold and record the spectrum over the range 230-250 nm. Dilute an aliquot of the latter solution 10-fold and record the spectrum over the range 200-230 nm. Measure accurately the absorbance at 254 nm and calculate the molar extinction coefficient, preferably using 3 or more concentrations of the solution. 

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