Pharmaceutical Analytical Chemistry I: Group II Cations

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What is the purpose of washing the precipitated sulfides with 5% NH4NO3 solution?

To remove soluble cations of previous groups

To prevent precipitation of group I cations

To remove soluble cations of subsequent groups (correct)

To precipitate cations of subgroup II-A

Why is Lead (Pb2+) often found in Group II?

Because it always precipitates with Group I cations

Because it is not affected by H2S

Because it precipitates with dilute HCl but incompletely (correct)

Because it does not precipitate with HCl

What is the reagent used for the separation of Group II A and B cations?

Dilute HCl

5% NH4NO3 solution

H2S in acidic medium

NaOH with yellow ammonium sulfide (NH4)2SX (correct)

What happens when excess ammonium poly sulfides are used in the separation process?

Much colloidal sulfur precipitates Signup and view all the answers

What is the purpose of washing the sulfides thoroughly before separation of subgroups 2A and 2B?

To remove H2S Signup and view all the answers

What would be the consequence of not washing the sulfides thoroughly before separation of subgroups 2A and 2B?

Mercuric would escape to group 2B Signup and view all the answers

What is the first step in the separation of Group II-A cations?

Reacting with H2S in acid medium to form PPT Signup and view all the answers

What is the purpose of using H2S in acidic medium in the separation process?

To precipitate Group II cations Signup and view all the answers

What is the role of methyl violet indicator in the precipitation of Group II cations?

To adjust the acidity of the solution Signup and view all the answers

What is the effect of adding strong acids to the solution in the precipitation of Group II cations?

It shifts the equilibrium to the left, decreasing the concentration of sulfide ions Signup and view all the answers

What is the pH at which the precipitation of Group II cations is typically carried out?

pH = 0.5 Signup and view all the answers

What is the result of heating the spot formed on a polished Cu surface with a Bunsen flame?

The copper surface becomes visible again Signup and view all the answers

Why do sulfides of Group II cations precipitate in acidic medium?

Because they have low solubility products Signup and view all the answers

What is the purpose of adding NaOH solution dropwise to SnCl2?

To form a white precipitate of Sn(OH)2 Signup and view all the answers

What happens to the sulfides of Group IV cations in acidic medium?

They precipitate partially Signup and view all the answers

What is the effect of increasing the acidity of the solution beyond 0.3M HCl?

PbS, CdS, and SnS precipitate partially Signup and view all the answers

What is the result of adding pyrogallol to a hot, faintly acidic solution of Bi3+?

A yellow precipitate is formed Signup and view all the answers

What is the purpose of adding H2S to the solution after adjusting the acidity?

To convert the oxy salts into sulfide precipitates Signup and view all the answers

What is the purpose of washing the white precipitate of Bi(OH)3 with water?

To discard the washing Signup and view all the answers

Why are the sulfides of Group II cations precipitated in the presence of a very low concentration of sulfide ions?

Because they have low solubility products Signup and view all the answers

What is the result of heating a black residue of HgS on a low flame?

The residue dissolves in Aqua regia Signup and view all the answers

Why is it necessary to remove Sb before performing the pyrogallol test for Bi3+?

Sb interferes with the test Signup and view all the answers

What is the result of reacting Bi3+ with sodium tetrahydroxostannite?

A black precipitate of Biº is formed Signup and view all the answers

What is the purpose of polishing a Cu sheet or coin before performing the Hg2+ test?

To obtain a glittery, silver-like spot Signup and view all the answers

What is the result of adding iron powder to the acidified solution of [Cu(NH3)4]2+ and [Cd(NH3)4]2+?

A red deposit of copper is obtained Signup and view all the answers

What is the purpose of adding H2S to the neutralized filtrate?

To precipitate cadmium sulphide Signup and view all the answers

What is the purpose of treating the extract of group IIB sulfides with 6-8 M HCl?

To make the solution slightly acidic Signup and view all the answers

Why is 6-8 M HCl preferred over conc. HCl for acidification?

Because it does not dissolve As2S3 Signup and view all the answers

What is the color of the precipitate if only sulphur is present?

Fine white or light yellow Signup and view all the answers

What is the significance of the color of the precipitate in the identification of subgroup II-B cations?

It indicates which member of the subgroup is present Signup and view all the answers

What is the basis of separation of arsin sulfides from Sb and Sn sulfides?

Solubility in conc. HCl Signup and view all the answers

What is the purpose of filtering the precipitates of copper and excess iron?

To separate copper from iron Signup and view all the answers

What is used to separate arsin sulfides from other interfering PPTs?

Ammonium carbonate solution Signup and view all the answers

What happens when a solution containing Sb3+ and Sn4+ is treated with iron wire and in the presence of H+?

Only Sb3+ is precipitated as a black PPT. Signup and view all the answers

What is formed when a solution containing arsenic is acidified with acid?

A yellow precipitate of As2S3 and As2S5 Signup and view all the answers

What is used to make the solution slightly alkaline in the identification of arsenic?

Ammonia Signup and view all the answers

What is produced when the black residue of Sb metal is dissolved in aqua regia?

SbCl3 and SnCl4 Signup and view all the answers

What is the purpose of adding oxalic acid in the identification of antimony?

To form a complex with tin Signup and view all the answers

What is formed when H2S gas is passed into the hot solution containing SbCl3 and SnCl4?

An orange precipitate of Sb2S3 Signup and view all the answers

What is used to test for tin (Sn4+) in the filtrate?

Oxalic acid Signup and view all the answers