10 gm of pesticide sample containing arsenic was treated appropriately to convert its arsenic content to AsO 4 3 − . Then 25 ml of 0.045 M − AgNO 3 was added to precipitate AsO 4 3 − as Ag 3 A

Question

10 gm of pesticide sample containing arsenic was treated appropriately to convert its arsenic content to AsO 4 ​ 3 − . Then 25 ml of 0.045 M − AgNO 3 ​ was added to precipitate AsO 4 ​ 3 − as Ag 3 ​ AsO 4 ​ . The precipitate was filtered and the unreacted AgNO 3 ​ present in the filtrate was then titrated with 0.05 M potassium thiocyanate. The observed titre value was 5.0 ml . Calculate the percentage of arsenic as AsO 4 ​ 3 − in the pesticide sample. ( As = 75 )

TestHub · Accepted Answer

Initial moles of Ag⁺ added: 25 m L × 0.045 M = 1.125 mm o l Unreacted moles of Ag⁺ titrated: 5.0 m L × 0.05 M = 0.25 mm o l Reacted moles of Ag⁺ with AsO₄³⁻: 1.125 − 0.25 = 0.875 mm o l Moles of AsO₄³⁻ precipitated: 3 0.875 ​ = 0.2917 mm o l (based on Ag₃AsO₄ stoichiometry) Percentage of AsO₄³⁻: 10 g 0.2917 × 1 0 − 3 m o l × 139 g / m o l ​ × 100% = 0.40%

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