6.2 g of a sample containing `NaHCO_(3)`, `NaHCO_(3)` and non -volatiale inert impurity on gentle heating loses 5% of its mass due to reaction `2NaHCO_(3)to Na_(2)CO_(3)+H_(2)O+CO_(2).` Residue is dissolved in water and formed 100 mL solution and its 10 mL portion requires 7.5 mL of 0.2 M aqueous solution of `BaCl_(2)` for complete precipitation of carbonates.
Determine mass (in gram) of `Na_(2)CO_(3)` in the original sample .