29 Questions
What is the primary reason for using cold HCl in the precipitation reaction?
To prevent PbCl2 from escaping to group II
Why is dilute HCl used instead of concentrated HCl?
To prevent PbCl2 from forming soluble complexes
What is the purpose of adding a slight excess of HCl with stirring?
To ensure complete precipitation by the common ion effect
What is the purpose of centrifugation after precipitation?
To separate the precipitate from the supernatant
What is the solubility product (Ksp) of Hg2Cl2?
1.0 x 10^-18
What is the result of the common ion effect in reaction 2?
The reaction moves to the left, preventing the dissolution of AgCl
What is the purpose of adding KI to centrifugate 1?
To form a soluble complex
Why is it necessary to acidify centrifugate 2 with dil HNO3?
To break down the silver amine complex and form a white ppt of AgCl
What is the reason for not adding strong acid or alkali in the pot chromate test?
Because it will form a soluble lead dichromate
What is the result of adding H2SO4 to centrifugate 1?
A white precipitate of lead sulphate is formed
Why is AgCl soluble in dil NH3?
Because the silver amine complex has low stability
What is the effect of adding acid to a silver amine complex?
Conversion of NH3 to NH4+
Why does the addition of KI to [Ag(NH3)2]Cl result in a yellow precipitate of silver iodide?
Because Ag+ reacts with KI to form an insoluble precipitate
What is the purpose of heating the solution after adding aqua regia to the mercury-containing precipitate?
To evaporate excess aqua regia
What is the group reagent used for the precipitation of cations in Group II (A, B)?
Dil HCl + H2S
What is the result of the reaction between Hg2+2 and KI?
Formation of a scarlet red precipitate of mercuric iodide
What are the three steps involved in the identification of cations?
Precipitation, Separation, Identification
What is the purpose of adjusting the sulphide ion concentration in the precipitation process of groups II and IV?
To selectively precipitate group II cations while leaving group IV cations in solution
Why is dilute HCl used instead of concentrated HCl in the precipitation process?
To prevent the precipitation of group IV cations
What is the role of the common ion effect in the precipitation process?
To decrease the ionization of H2S
What is the consequence of using higher acidity than 0.3 N HCl in the precipitation process?
Incomplete precipitation of group II cations
Why is it important to adjust the acidity of the reaction mixture in the precipitation process?
To maintain a suitable sulphide ion concentration
What is the suitable acidity range for the precipitation of group II cations?
0.2 - 0.3 N HCl
What is the role of KCN in the test for Cd2+?
It acts as a masking agent for Cu
What is the color of the precipitate formed when Cd2+ reacts with H2S?
White
Why is the cadmicyanide complex [Cd(CN)4]2- unstable?
Because it yields sufficient Cd2+ to react with H2S
What is the purpose of the steps of precipitation, separation, and identification in the testing of cations?
To confirm the presence of a specific cation
Which group of cations is precipitated as hydroxides using NH4Cl and NH4OH?
Group III
What is the name of the complex formed when Cu2+ reacts with NH3?
Cupric ammonium complex
Learn about the steps involved in identifying cations, specifically Group I cations such as Pb+2, Ag+, and Hg2+2, through precipitation reactions. Understand the role of chloride salts and the use of diluted HCl as a reagent.
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