40 Questions
What is the purpose of washing the precipitated sulfides with 5% NH4NO3 solution?
To remove soluble cations of subsequent groups
Why is Lead (Pb2+) often found in Group II?
Because it precipitates with dilute HCl but incompletely
What is the reagent used for the separation of Group II A and B cations?
NaOH with yellow ammonium sulfide (NH4)2SX
What happens when excess ammonium poly sulfides are used in the separation process?
Much colloidal sulfur precipitates
What is the purpose of washing the sulfides thoroughly before separation of subgroups 2A and 2B?
To remove H2S
What would be the consequence of not washing the sulfides thoroughly before separation of subgroups 2A and 2B?
Mercuric would escape to group 2B
What is the first step in the separation of Group II-A cations?
Reacting with H2S in acid medium to form PPT
What is the purpose of using H2S in acidic medium in the separation process?
To precipitate Group II cations
What is the role of methyl violet indicator in the precipitation of Group II cations?
To adjust the acidity of the solution
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
What is the pH at which the precipitation of Group II cations is typically carried out?
pH = 0.5
What is the result of heating the spot formed on a polished Cu surface with a Bunsen flame?
The copper surface becomes visible again
Why do sulfides of Group II cations precipitate in acidic medium?
Because they have low solubility products
What is the purpose of adding NaOH solution dropwise to SnCl2?
To form a white precipitate of Sn(OH)2
What happens to the sulfides of Group IV cations in acidic medium?
They precipitate partially
What is the effect of increasing the acidity of the solution beyond 0.3M HCl?
PbS, CdS, and SnS precipitate partially
What is the result of adding pyrogallol to a hot, faintly acidic solution of Bi3+?
A yellow precipitate is formed
What is the purpose of adding H2S to the solution after adjusting the acidity?
To convert the oxy salts into sulfide precipitates
What is the purpose of washing the white precipitate of Bi(OH)3 with water?
To discard the washing
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
What is the result of heating a black residue of HgS on a low flame?
The residue dissolves in Aqua regia
Why is it necessary to remove Sb before performing the pyrogallol test for Bi3+?
Sb interferes with the test
What is the result of reacting Bi3+ with sodium tetrahydroxostannite?
A black precipitate of Biº is formed
What is the purpose of polishing a Cu sheet or coin before performing the Hg2+ test?
To obtain a glittery, silver-like spot
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
What is the purpose of adding H2S to the neutralized filtrate?
To precipitate cadmium sulphide
What is the purpose of treating the extract of group IIB sulfides with 6-8 M HCl?
To make the solution slightly acidic
Why is 6-8 M HCl preferred over conc. HCl for acidification?
Because it does not dissolve As2S3
What is the color of the precipitate if only sulphur is present?
Fine white or light yellow
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
What is the basis of separation of arsin sulfides from Sb and Sn sulfides?
Solubility in conc. HCl
What is the purpose of filtering the precipitates of copper and excess iron?
To separate copper from iron
What is used to separate arsin sulfides from other interfering PPTs?
Ammonium carbonate solution
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.
What is formed when a solution containing arsenic is acidified with acid?
A yellow precipitate of As2S3 and As2S5
What is used to make the solution slightly alkaline in the identification of arsenic?
Ammonia
What is produced when the black residue of Sb metal is dissolved in aqua regia?
SbCl3 and SnCl4
What is the purpose of adding oxalic acid in the identification of antimony?
To form a complex with tin
What is formed when H2S gas is passed into the hot solution containing SbCl3 and SnCl4?
An orange precipitate of Sb2S3
What is used to test for tin (Sn4+) in the filtrate?
Oxalic acid
This quiz covers the analysis of Group II cations, including their reactions with hydrogen sulfide in acidic medium. It's suitable for second-year dentistry students.
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