Identification of Cations (Group I) by Precipitation

What is the primary reason for using cold HCl in the precipitation reaction?

To increase the concentration of Cl- ions
To prevent PbCl2 from escaping to group II (correct)
To increase the solubility of PbCl2
To decrease the rate of precipitation

Why is dilute HCl used instead of concentrated HCl?

To increase the rate of precipitation
To decrease the solubility of PbCl2
To increase the concentration of Cl- ions
To prevent PbCl2 from forming soluble complexes (correct)

What is the purpose of adding a slight excess of HCl with stirring?

To decrease the concentration of Cl- ions
To ensure complete precipitation by the common ion effect (correct)
To decrease the rate of precipitation
To increase the solubility of PbCl2

What is the purpose of centrifugation after precipitation?

To separate the precipitate from the supernatant (B) Signup and view all the answers

What is the solubility product (Ksp) of Hg2Cl2?

1.0 x 10^-18 (C) Signup and view all the answers

What is the result of the common ion effect in reaction 2?

The reaction moves to the left, preventing the dissolution of AgCl (D) Signup and view all the answers

What is the purpose of adding KI to centrifugate 1?

To form a soluble complex (C) Signup and view all the answers

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 (B) Signup and view all the answers

What is the reason for not adding strong acid or alkali in the pot chromate test?

Because it will form a soluble lead dichromate (C) Signup and view all the answers

What is the result of adding H2SO4 to centrifugate 1?

A white precipitate of lead sulphate is formed (C) Signup and view all the answers

Why is AgCl soluble in dil NH3?

Because the silver amine complex has low stability (B) Signup and view all the answers

What is the effect of adding acid to a silver amine complex?

Conversion of NH3 to NH4+ (A) Signup and view all the answers

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 (C) Signup and view all the answers

What is the purpose of heating the solution after adding aqua regia to the mercury-containing precipitate?

To evaporate excess aqua regia (C) Signup and view all the answers

What is the group reagent used for the precipitation of cations in Group II (A, B)?

Dil HCl + H2S (A) Signup and view all the answers

What is the result of the reaction between Hg2+2 and KI?

Formation of a scarlet red precipitate of mercuric iodide (C) Signup and view all the answers

What are the three steps involved in the identification of cations?

Precipitation, Separation, Identification (D) Signup and view all the answers

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 (D) Signup and view all the answers

Why is dilute HCl used instead of concentrated HCl in the precipitation process?

To prevent the precipitation of group IV cations (D) Signup and view all the answers

What is the role of the common ion effect in the precipitation process?

To decrease the ionization of H2S (D) Signup and view all the answers

What is the consequence of using higher acidity than 0.3 N HCl in the precipitation process?

Incomplete precipitation of group II cations (B) Signup and view all the answers

Why is it important to adjust the acidity of the reaction mixture in the precipitation process?

To maintain a suitable sulphide ion concentration (A) Signup and view all the answers

What is the suitable acidity range for the precipitation of group II cations?

0.2 - 0.3 N HCl (A) Signup and view all the answers

What is the role of KCN in the test for Cd2+?

It acts as a masking agent for Cu (C) Signup and view all the answers

What is the color of the precipitate formed when Cd2+ reacts with H2S?

White (C) Signup and view all the answers

Why is the cadmicyanide complex [Cd(CN)4]2- unstable?

Because it yields sufficient Cd2+ to react with H2S (B) Signup and view all the answers

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 (C) Signup and view all the answers

Which group of cations is precipitated as hydroxides using NH4Cl and NH4OH?

Group III (D) Signup and view all the answers

What is the name of the complex formed when Cu2+ reacts with NH3?

Cupric ammonium complex (C) Signup and view all the answers