A mixture of salts was treated to determine the barium content. A 0.230g sample was dissolved and treated with excess potassium chromate. The precipitate of BaCrO 4 was dissolved in dil HCl to convert BaCrO 4 to Cr 2 O 7 2 - anion. The solution treated with excess sodium iodide and tri Iodide produced was titrated with 21 mL of 0.095 M sodium thiosulphate. Calculate the % of BaCl 2 ⋅ 2 H 2 O in the sample. [given Molar Mass of BaCl 2.2H2O = 244]

Question

A mixture of salts was treated to determine the barium content. A 0.230g sample was dissolved and treated with excess potassium chromate. The precipitate of BaCrO 4 was dissolved in dil HCl to convert BaCrO 4 to Cr 2 O 7 2 - anion. The solution treated with excess sodium iodide and tri Iodide produced was titrated with 21 mL of 0.095 M sodium thiosulphate. Calculate the % of BaCl 2 ⋅ 2 H 2 O in the sample. [given Molar Mass of BaCl 2.2H2O = 244], 70.5 %, 30.25 %, 15.12 %, 110 %

MARKS App · Accepted Answer

The skeletal reactions are BaCrO 4 + HCl ⟶ Cr 2 O 7 2 - + Ba 2 + Cr 2 O 7 2 - + I - ⟶ Cr 3 + + I 3 - I 3 - 1 + S 2 O 3 2 - ⟶ S 4 O 6 2 - + I - Meqs of Na 2 S 2 O 3 = 21 x 0.095 x 1 = 1.995 Meqs of I 3 - ≡ Meqs of Cr 2 O 7 2 - mM of Cr 2 O 7 2 - = 1 . 9 9 5 6 mM of Cr O 4 2 - = 1 . 9 9 5 6 × 2 = 0 . 6 6 5 mM of BaCrO 4 Mass % of BaCl 2 . 2H 2 O = 0 . 6 6 5 × 1 0 - 3 × 2 4 4 0 . 2 3 0 × 1 0 0 = 7 0 . 5 %

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