Identifying unknown carboxylic acid

An unknown organic arboxylic acid, melting point = 139-141 degrees C, burned with a yellow, sooty flame. The sodium fusion test showed that nitrogen was present. It did not react with p-toluenesulfonyl chloride, but did give a positive test when tested with 5% aqueous ferrous ammonium sulfate solution, acidified with 3 N H2SO4 and then followed by methanolic KOH solution. A 200-mg sample of the acid neutralized 12.4 mL of 0.098 N sodium hydroxide solution. Identify the acid. Does your structure agree with the calculated equivalent weight?