ANIONS 2

• Group 2 anions contains only the chromate and sulfate ions
• Group 2 anions are precipitated by the group reagent, barium acetate, in slightly basic solution.
• The analysis of this group involves no difficulties because the presence of chromate ions shows yellow color.
• Precipitate may be composed of Barium Chromate and Barium Sulfate
• Addition of hydrochloric acid dissolves Barium chromate. Thus, precipitate is Barium sulfate while centrifugate is solution with chromate ions
• Initial detection in identifying sulfate ions: White precipitate in the precipitation with Barium acetate
• First is oxidation to sulphate by hydrogen peroxide. Then, sulfate is insoluble as Barium sulfate, thus the white precipitate.
• Confirmatory reagent for sulfate ions: hydrochloric acid
• Positive indicator for sulfate ion: white precipitate
• The addition of sodium acetate to the acidic chromic solution lowers the Hydrogen ion concentration sufficiently to permit reprecipitation of Barium chromate, the yellow precipitate
• Sodium acetate serves as the buffer solution.
• The presence of chromate ion may be confirmed by the addition of hydrogen peroxide
• confirmatory reagent for chromate ion: sodium acetate
• positive indicator for chromate ion: yellow precipitate