Group II Cations Overview
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Questions and Answers

What is the group reagent for the cations of Group II?

The group reagent for cations of Group II is hydrogen sulphide in acid medium, specifically 0.3 M HCl.

How does an increase in H+ concentration affect the concentration of S2- ions?

An increase in H+ concentration shifts the equilibrium to the left, decreasing the concentration of S2- ions.

What is required to precipitate cations of Group II?

A relatively small amount of sulphide ion is required to precipitate cations of Group II, controlled by the pH level.

What happens if the acidity is decreased below 0.3 M HCl?

<p>Decreasing the acidity below 0.3 M HCl leads to precipitation of sulphides of group IIIB and dissolution of sulphides of group IIB.</p> Signup and view all the answers

Why is controlling the [H+] important in the precipitation process?

<p>Controlling the [H+] is crucial because it influences the [S2-] concentration, which determines whether precipitation occurs.</p> Signup and view all the answers

What is the significance of a 0.3 M HCl concentration in relation to S2-?

<p>At 0.3 M HCl, the concentration of S2- is 1.5 x 10^-19 M, which is sufficient to precipitate the sulphides of Group II cations.</p> Signup and view all the answers

How does increasing the acidity above 0.3 M HCl affect Group II cations?

<p>Increasing the acidity above 0.3 M HCl prevents the precipitation of CdS, PbS, and SnS2, forming stable soluble complexes instead.</p> Signup and view all the answers

What is the role of sodium sulphide (Na2S) and sodium hydroxide (NaOH) in the categorization of Group II cations?

<p>Sodium sulphide (Na2S) and sodium hydroxide (NaOH) are used to evaluate the solubility and behavior of cations in forming thioanions and oxyanions.</p> Signup and view all the answers

What color precipitate forms when arsenious ion (As3+) reacts with hydrogen sulfide (H2S)?

<p>Yellow precipitate (As2S3)</p> Signup and view all the answers

How do arsenious and arsenic sulfides react to hydrochloric acid (HCl)?

<p>They are insoluble in 12 M HCl but partially soluble upon boiling.</p> Signup and view all the answers

What color precipitate results from the reaction of antimonous ion (Sb3+) with hydrogen sulfide (H2S)?

<p>Orange precipitate (Sb2S3)</p> Signup and view all the answers

What solution can be used to dissolve arsenious and arsenic sulfides after their precipitation?

<p>Concentrated nitric acid (HNO3)</p> Signup and view all the answers

What is the confirmatory test for the presence of Sb3+ ions after their reaction with 12M HCl?

<p>Oxalic acid forms complexes with Sb3+ and Sn4+.</p> Signup and view all the answers

What confirmatory test can be performed after dissolving Sb3+ and Sb5+ with excess sodium thiosulfate?

<p>Formation of thio and oxyanions.</p> Signup and view all the answers

What is the color of the precipitate formed when arsenic ion (As5+) reacts with hydrogen sulfide (H2S)?

<p>Yellow precipitate (As2S5)</p> Signup and view all the answers

In what chemical state do arsenic and antimony ions exist in solution before precipitation?

<p>As3+, As5+, Sb3+, and Sb5+.</p> Signup and view all the answers

What happens to stannous sulphide (SnS) in the presence of NaOH or Na2S?

<p>Stannous sulphide (SnS) is incompletely soluble in either NaOH or Na2S.</p> Signup and view all the answers

What is the role of hydrogen peroxide in the oxidation of stannous ions (Sn2+)?

<p>Hydrogen peroxide oxidizes stannous ions (Sn2+) to stannic ions (Sn4+).</p> Signup and view all the answers

What is the confirmatory test for mercuric ion (Hg2+)?

<p>A confirmatory test for Hg2+ involves reacting it with ammonium hydroxide to produce white mercuric amino chloride.</p> Signup and view all the answers

How can bismuth (III) ion (Bi3+) be confirmed using excess water?

<p>Bi3+ reacts with water to form bismuth oxychloride (BiOCl), resulting in a white turbidity.</p> Signup and view all the answers

What color is produced when copper (II) ion (Cu2+) reacts with ammonium hydroxide?

<p>The reaction produces a deep blue color due to the formation of the complex ion [Cu(NH3)4]2+.</p> Signup and view all the answers

What is the color of cadmium sulfide (CdS) precipitate when Cd2+ reacts with H2S?

<p>CdS precipitate appears yellow when Cd2+ reacts with H2S.</p> Signup and view all the answers

Which cations belong to Group II A?

<p>Group II A includes Hg2+, Bi3+, Cu2+, Cd2+, and Pb2+.</p> Signup and view all the answers

What happens to arsenious ion (As3+) and arsenic ion (As5+) under group IIB precipitation conditions?

<p>Both As3+ and As5+ form precipitates of their respective sulfides under group IIB conditions.</p> Signup and view all the answers

What occurs when excess potassium iodide (KI) is added to copper (II) ion (Cu2+)?

<p>Excess KI leads to the formation of cuprous iodide (Cu2I2), resulting in a white precipitate and iodine color change.</p> Signup and view all the answers

Describe the precipitation reaction of mercuric ion (Hg2+) with H2S.

<p>Hg2+ reacts with H2S to form a black precipitate of mercuric sulfide (HgS).</p> Signup and view all the answers

Study Notes

Group II Cations Overview

  • Group II cations are separated into two subgroups: II-a and II-b.
  • The group reagent for Group II cations is hydrogen sulfide (H2S) in an acidic medium (0.3 M HCl).
  • The basis for the subdivision into II-a and II-b subgroups is the solubility of their sulfides in excess sodium sulfide (Na2S) or sodium hydroxide (NaOH) to form thioanions and oxyanions.

Group II A Cations

  • Group II-a cations include: mercuric (Hg2+), bismuth (Bi3+), copper (Cu2+), cadmium (Cd2+), and lead (Pb2+).
  • These cations form insoluble sulfides in an acidic medium (0.3 M HCl).
  • The precipitation of Group II-a sulfides is controlled by the sulfide ion concentration ([S2-]), which is influenced by the hydrogen ion concentration ([H+]).
  • The solubility product of Group II-a sulfides is lower than that of Group II-b sulfides, requiring smaller amounts of sulfide ions for precipitation.

Mercuric (Hg2+)

  • Mercuric ions precipitate as black mercury sulfide (HgS).
  • Confirmatory tests for mercuric ions include:
    • The formation of white mercuric amino chloride (Hg(NH2)Cl) with ammonium hydroxide.
    • The reduction of mercuric ions to mercurous ions (Hg2+) with stannous chloride (SnCl2), forming white mercurous chloride (Hg2Cl), which can be further reduced to black mercury (Hgo).
    • The formation of scarlet red mercuric iodide (HgI2) with potassium iodide (KI), which can further react with excess KI to form a soluble complex ([HgI4]2-).

Bismuth (Bi3+)

  • Bismuth ions precipitate as dark brown bismuth sulfide (Bi2S3).
  • Confirmatory tests for bismuth ions include:
    • The formation of white bismuth oxychloride (BiOCl) upon the addition of excess water, forming a turbidity.
    • The reduction of bismuth ions to black metallic bismuth (Bi) with freshly prepared sodium stannite ([HSnO2]-).

Copper (Cu2+)

  • Copper ions precipitate as black copper sulfide (CuS).
  • Confirmatory tests for copper ions include:
    • The formation of a deep blue solution containing tetraamminecopper(II) ([Cu(NH3)4]2+) upon the addition of ammonium hydroxide.
    • The formation of white cuprous iodide (Cu2I2) with potassium iodide (KI) and the simultaneous release of brown iodine.
    • The formation of a chocolate brown precipitate of copper(II) hexacyanoferrate(II) (Cu2[Fe(CN)6]) with potassium ferrocyanide ([Fe(CN)6]4-) in an acidic medium.

Cadmium (Cd2+)

  • Cadmium ions precipitate as yellow cadmium sulfide (CdS).
  • Cadmium sulfide is insoluble in excess sodium sulfide (Na2S) and sodium hydroxide (NaOH).

Group II B Cations

  • Group II-b cations include: arsenious (As3+), arsenic (As5+), antimonous (Sb3+), antimonic (Sb5+), and stannic (Sn4+).
  • These cations form sulfides that are soluble in excess sodium sulfide (Na2S) or sodium hydroxide (NaOH).
  • To separate Group II-b sulfides from Group II-a sulfides, the mixture is boiled with hydrogen peroxide (H2O2), which oxidizes stannous (Sn2+) to stannic (Sn4+).

Arsenious (As3+) and Arsenic (As5+)

  • Both arsenious and arsenic ions precipitate as yellow sulfides: arsenious sulfide (As2S3) and arsenic sulfide (As2S5), respectively.
  • These sulfides are soluble in excess sodium sulfide (Na2S) or sodium hydroxide (NaOH).
  • Arsenious sulfide and arsenic sulfide are insoluble in 12 M hydrochloric acid (HCl) but can be partially dissolved by boiling.
  • Confirmatory tests for arsenic ions involve dissolving the sulfides in concentrated nitric acid (HNO3) to form arsenic acid (H3AsO4) and then performing the ammonium molybdate test.

Antimonous (Sb3+) and Antimonic (Sb5+)

  • Both antimonous and antimonic ions precipitate as orange sulfides: antimonous sulfide (Sb2S3) and antimonic sulfide (Sb2S5), respectively.
  • These sulfides are soluble in excess sodium sulfide (Na2S) or sodium hydroxide (NaOH).
  • Antimonous sulfide and antimonic sulfide can be dissolved in 12 M hydrochloric acid (HCl).
  • Confirmatory tests for antimony ions involve dissolving the sulfides in 12 M HCl and then performing the following tests:
    • Formation of an oxysalt, which is a white turbidity when water is added to the solution.
    • The addition of sodium thiosulphate (Na2S2O3).
    • To test specifically for Sb3+ when Sn4+ is present, oxalic acid is added, which forms complexes with both ions.

Stannic (Sn4+)

  • Stannic ions precipitate as brown stannic sulfide (SnS2).
  • After boiling with hydrogen peroxide (H2O2) to oxidize stannous ions (Sn2+) to stannic ions (Sn4+), stannic sulfide is soluble in excess sodium sulfide (Na2S) or sodium hydroxide (NaOH).
  • The excess hydrogen peroxide must be decomposed by boiling to prevent oxidation of the hydrogen sulfide reagent to colloidal sulfur.

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Cations of Group II PDF

Description

This quiz covers the characteristics and classification of Group II cations, with an emphasis on their subdivision into Group II-a and II-b. It includes the behavior of mercuric, bismuth, copper, cadmium, and lead cations in an acidic medium and their precipitation reactions. Test your knowledge on the solubility and reactions of these important cations.

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