15. Solving a chemistry problem

42. Give the reaction equations for the quantitative determination of sodium ethaminal (Mg 248.26) by acidimetry (FS). Specify the indicator (name, formula, color transition at the end point of the titration).
Calculate the content of etaminal sodium in terms of dry matter (%), if 19.9 ml of 0.1 mol/l hydrochloric acid solution (K=0.98) was used for titration of a sample weighing 0.5024 g. When calculating, take into account the content of free alkali in etaminal sodium (MrNaOH 40.0), which amounted to 0.3%. Weight loss on drying etaminal-sodium 4.5%.