113. Solving a chemistry problem

2. A weighing of 0.4 g of technical sodium hydroxide was dissolved in a volumetric flask with a capacity of 100 ml. For titration of 20 ml of a solution with methyl orange, 19.2 ml of an HCl solution were used (T(HCl)=0.0036). The same sample of the solution was treated with 2M BaCl2 until the carbonates were completely precipitated, and 18 ml of the HCl solution was consumed during titration with phenolphthalein. Determine the mass fraction of Na2CO3 in the preparation. Answer 2.62%