74. Solving a chemistry problem

73. A portion of sodium carbonate weighing 0.2458 g was dissolved and 20 ml of a 0.045 M solution of magnesium sulfate was added to the solution. The excess of the latter was titrated with 15 ml of complexone III solution (1 ml of magnesium sulfate is equivalent to 1.25 ml of complexone III). Write reaction equations. Describe the scheme of analysis, pH of the solution, indicate the buffer solutions.