A 50 ml solution suspected of containing ammonium ions was diluted to 250 mL A 50.0 mL aliquot of the diluted solution was analysed by Back-Titration. A 100 mL aliquot of a std 0.2005 M NaOH (MM = 40 g/mol) solution was added to the solution. The excess NaOH was back-titrated with 25.0 mL of a 0.1204 M std HCI (36/45 g/mol). The concentration of the ammonium ion (MM-18.04) in the initial sample solution (in g/dm) is:​