49. To determine ammonium nitrogen, a 2.6351 g sample of fertilizer was dissolved in a 250.0 ml volumetric flask. Formaldehyde was added to 25.00 ml of the resulting solution and the released acid was titrated with 18.72 ml of NaOH solution [T(NaOH)=0.003987]. 0.50 ml of NaOH was used for titration of formaldehyde in a blank experiment. Calculate the mass fraction (%) of nitrogen in the fertilizer.

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