2. From a sample of fluorapatite weighing 1,000 g, fluorine was isolated by distillation. The distillate was neutralized with NaOH solution to pH 3.5. Then the hot solution of K2SiF6 was titrated with 9.85 ml of 0.1M NaOH (K=1.023) with phenolphthalein:
K2SiF6+4NaOH=2KF+4NaF+SiO2+2H2O
Calculate the mass fraction (%) of fluorine in the sample. Answer: 2.87%

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