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

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