Confirmation Test for Arsenic and Antimony Ions

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Questions and Answers

What is used to buffer the acidity of the nitric acid solution of the arsenate ion?

Silver nitrate

Sodium acetate (correct)

Sodium chloride

Acetic acid

What color precipitate is formed when silver nitrate solution is added to a neutral solution of an arsenate?

White

Yellow

Reddish-brown (correct)

Green

What accelerates the precipitation of metallic antimony from solutions of antimony compounds?

Adding sodium hypochlorite

Mixing with lead solution

Introducing mercury vapor

Using metallic tin in contact with a silver coin (correct)

How is arsenic distinguished from antimony in the confirmatory test using metallic tin?

Antimony forms a black powder on a silver coin. Signup and view all the answers

What soluble anions are formed when the sulfides of tin and antimony are dissolved in conc. HCl?

SbCl3- and SnCl6- Signup and view all the answers

What is the confirmatory test for the presence of lead ion in Group IIA analysis?

Formation of a yellow precipitate of lead chromate Signup and view all the answers

To identify the presence of bismuth ion, what reaction serves as the confirmatory test?

Reduction of Bi(OH)3 to black metallic bismuth by stannite ion Signup and view all the answers

How can the presence of cupric ion be identified in Group IIA analysis?

Formation of a deep blue color complex ion Cu(NH3)4++ Signup and view all the answers

What precaution should be taken with hydronium ions to prevent the formation of Pb[HSO4]2?

Avoiding it to prevent soluble Pb[HSO4]2 formation Signup and view all the answers

Which compound is used to precipitate bismuth ion in the presence of cupric and cadmium ions?

Bi(OH)3 by excess ammonia Signup and view all the answers

What is the formation of a yellow precipitate a confirmatory test for?

Lead ion Signup and view all the answers

What color is cupric ferrocyanide?

Reddish-brown Signup and view all the answers

Which ion interferes with the identification test for cadmium ion?

Cu(H2O)4++ Signup and view all the answers

What complex does cyanide form with copper ions?

Cu(CN)3- Signup and view all the answers

What happens when a mixture of Cu(CN)3- and Cd(CN)4- ions is treated with H2S?

Cadmium complexes are destroyed, and yellow cadmium sulfide precipitates Signup and view all the answers

What happens when the alkaline centrifugate from Group II separation is acidified?

The complex ions are destroyed, and ions of Group I precipitate as sulfides Signup and view all the answers

Which sulfides dissolve when reacted with concentrated hydrochloric acid?

Antimonous sulfide and stannic sulfide Signup and view all the answers

Study Notes

Acid-Base Buffering and Precipitation Reactions

To buffer the acidity of nitric acid solutions containing arsenate ions, a basic agent such as sodium hydroxide or ammonium hydroxide may be used.
When silver nitrate solution is added to a neutral solution of arsenate, a yellow precipitate of silver arsenate is formed.
Precipitation of metallic antimony from antimony compounds is accelerated by the addition of reducing agents like zinc or iron.

Distinction Between Arsenic and Antimony

In the confirmatory test with metallic tin, arsenic is distinguished from antimony by the different reactions in acidic solutions; arsenic produces a gray precipitate while antimony produces a black precipitate.

Soluble Anions and Confirmatory Tests

Upon dissolving the sulfides of tin and antimony in concentrated hydrochloric acid, soluble anions such as sulfides and chlorides are formed.
For lead ion confirmation in Group IIA analysis, adding sodium hydroxide produces a white precipitate of lead(II) hydroxide.
Bismuth ion is confirmed by the formation of a yellow precipitate when bismuth is treated with potassium iodide.

Identification and Precautionary Measures

The presence of cupric ions in Group IIA analysis can be identified through complexation reactions, where cupric forms a blue solution.
When handling hydronium ions, caution should be exercised to prevent the formation of insoluble lead(II) sulfate (Pb[HSO4]2), which may complicate analyses.
Bismuth ion is precipitated in the presence of cupric and cadmium ions using sodium sulfide.

Precipitation Reactions and Color Indicators

The formation of a yellow precipitate indicates the presence of bismuth ions in solution.
Cupric ferrocyanide exhibits a blue color, often utilized in qualitative analysis to confirm the presence of cupric ions.
Cadmium ion identification tests may be interfered with by the presence of lead ions, which can form similar precipitates.

Complex Formation and Ion Reactions

Cyanide ions form soluble complexes with copper ions, specifically cupric cyanide, which can affect precipitation reactions.
Treating a mixture containing Cu(CN)3- and Cd(CN)4- with hydrogen sulfide results in the precipitation of sulfides, which can be used for further qualitative analysis.
Acidifying the alkaline centrifugate from Group II separation can lead to the re-precipitation of sulfides and other ions that were previously separated.
Sulfides of lead, zinc, and cadmium dissolve in concentrated hydrochloric acid to form soluble chlorides.

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Description

Learn about the confirmation test for arsenic and antimony ions using nitric acid, sodium acetate, and silver nitrate solutions. Understand how the reactions lead to the formation of characteristic precipitates for identification purposes.