20. From a sample of technical sodium hydroxide weighing 3.1496 g, containing sodium carbonate as the main impurity, 1.00 l of solution was prepared. For titration of 10.00 ml of the resulting solution in the presence of phenolphthalein (pT 9.0), 7.36 ml of a 0.1000 M HCl solution was used, and for titration of the same volume of solution in the presence of methyl orange (pT 4.0) - 7.52 ml HCl solution. Find the mass fraction (%) of NaOH and Na2CO3 in the sample. Mol. mass: (Na2CO3) 105.99; (NaOH) 40.00.

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