Given an unknown sample that could contain Cr 3+ , Mn 2+ , and/or Fe 2+ , you st

Question

Given an unknown sample that could contain Cr3+, Mn2+, and/or Fe2+, you strip the metal ions from the chalk using hydrochloric acid, concentrate the resulting solution, and add sodium hydroxide. You then add sodium hypochlorite and ammonium hydroxide. After boiling and centrifuging the product, you isolate the solution by decantation. You wash the remaining solid twice with water and sodium hydroxide. Then, water and sulfuric acid are added to this solid. The decanted solution is yellow, and you add barium chloride, boil and centrifuge. The resulting solid is washed and centrifuged, and nitric acid is added. Water is added and to the resulting orange solution, hydrogen peroxide is added, resulting in a blue solution. The solution made by adding sulfuric acid to the earlier solid is stirred, has hydrogen peroxide added to it, and then boiled. After adding water to the boiled solution, you separate it into two test tubes. To one tube you add potassium thiocyanate, and no color forms. To the second tube, you add a few grains of sodium bismuthate. You mix this solution and centrifuge. You observe a pink/purple solution.

A. Which cations are present in the unknown sample?

B. Which cations are not present in the unknown sample?

Explanation / Answer

Qualitative analysis of metal ions,

A. Mn2+ in presence of sodium bismuthate gives MnO4- which is purple/pink in color. So Mn2+ is present.

Cr3+ with H2O2 forms yellow colored CrO4- : Thus confirming Cr3+ is present in solution

B. No formation of [Fe(NCS)6]3- complex confirms absence of Fe2+ in solution

Related Questions

Navigate

• Browse (All)
• Browse G
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.