Chemistry Solubility and Cation Separation

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Questions and Answers

What is the role of FeSO4 in the detection of NO2- ions?

It neutralizes any acids in the solution, preventing false positives.

It reacts with CH3COOH to produce excess reactants.

It forms a brown ring complex indicating the presence of NO2-. (correct)

It directly reacts with NO2- to produce a colorless solution.

Why is NH4OH not used in the detection of chloride ions in the given reactions?

NH4OH does not react with AgCl.

Chloride ions react with NH4OH to form insoluble products.

AgBr is partially soluble in NH4OH, which may interfere with results. (correct)

Using NH4OH would lead to the immediate precipitation of all silver halides.

Which condition must be met when testing for NO3- ions?

The solution must not contain any Cl- ions.

The solution must be heated before adding FeSO4.

The solution must be acidic before adding H2SO4.

The solution must be free from NO2-, Br-, and I- ions. (correct)

What does the formation of the brown ring of [FeNO]2+ complex indicate?

Presence of NO3- ions in the solution. Signup and view all the answers

Which of the following reactions helps confirm the presence of NO2- ions?

NO2- + CH3COOH → CH3COO- + HNO2. Signup and view all the answers

What is the solubility product (Ksp) for the ions Ag+ and Cl- given their concentrations are both $1×10^{-5}$?

$1×10^{-10}$ Signup and view all the answers

If the ionic product is equal to the solubility product, what type of solution is formed?

Saturated solution Signup and view all the answers

What happens to the equilibrium of a weak electrolyte AB when a strong electrolyte containing the common ion is added?

Equilibrium shifts to the left Signup and view all the answers

What is the consequence of a solution becoming supersaturated?

Some cations precipitate out Signup and view all the answers

Which of the following describes the common ion effect?

Suppression of ionization of an electrolyte Signup and view all the answers

In the context of solubility product, when is a solution considered unsaturated?

When the ionic product is less than Ksp Signup and view all the answers

Why does the addition of HCl suppress the ionization of H2S?

HCl introduces a common ion Signup and view all the answers

How are cations classified in the context of solubility and precipitation?

According to their tendency of precipitation with specific group reagents Signup and view all the answers

What is produced when CuS is digested with concentrated nitric acid (HNO3)?

Cu(NO3)2 Signup and view all the answers

Which species precipitates first when a solution of Cu(NO3)2 and Cd(NO3)2 is treated with excess KCN?

Cd(CN)2 Signup and view all the answers

What is the stability constant (Kinst) for the precipitation of Cu(CN)2 compared to Cd(CN)2?

5.00×10-28 for Cu(CN)4 Signup and view all the answers

What is the primary reagent used to precipitate the IIA and IIB group cations?

Dilute hydrochloric acid and H2S gas Signup and view all the answers

How is Co2+ separated from Ni2+ in a solution?

By treating with NH4OH and NH4Cl Signup and view all the answers

Which of the following salts is formed when Sn2+ reacts with ammonium sulfide?

(NH4)2[SnS3] Signup and view all the answers

What are the end products formed after CoS and NiS are treated with aqua regia?

CoCl2 and NiCl2 Signup and view all the answers

What gas is released from the reaction of Cu(CN)2 as it decomposes?

CN2 Signup and view all the answers

What is the result of treating the IIB group cation precipitate with yellow ammonium sulfide?

It dissolves to give a clear solution Signup and view all the answers

What happens to the excess Cd++ ions in the solution treated with KCN?

They stay free in the solution. Signup and view all the answers

In the separation of IInd group cations, which cation is NOT part of the IIA group?

Sb3+ Signup and view all the answers

Which of the following complexes is formed when As2S3 reacts with ammonium sulfide?

(NH4)3[AsS4] Signup and view all the answers

What reagent is used to test for the presence of Co2+ ions in solution?

Amyl alcohol Signup and view all the answers

Which reaction is involved in separating Cu2+ from Cd2+ in qualitative analysis?

Cu2+ + H2S → CuS↓ Signup and view all the answers

What happens when excess H2S gas is added to a solution of IIA and IIB group cations?

A precipitate of cations forms Signup and view all the answers

Which of the following pairs represent cations that can be separated using the process described?

Co2+ and Ni2+ Signup and view all the answers

What is the main role of potassium persulfate (K2S2O8) in the separation of Cl-, Br-, and I-?

It acts as an oxidizing agent with a high oxidation potential. Signup and view all the answers

During the detection of I- using potassium persulfate, what indicates the successful confirmation of I-?

The evolution of violet fumes. Signup and view all the answers

In the tests for Br-, what is the significance of the brown vapors formed?

They confirm the presence of Br-. Signup and view all the answers

What is the chemical equation associated with the removal of I- using potassium persulfate?

2KI + K2S2O8 → K2SO4 + I2 ↑ Signup and view all the answers

What compound is formed when Cl- reacts with silver nitrate (AgNO3)?

AgCl Signup and view all the answers

When using chlorine water for separation, what does the violet color in the lower organic layer signify?

Presence of I-. Signup and view all the answers

Why is it important to avoid over-heating during the removal of I- using K2S2O8?

It may lead to the formation of unwanted products. Signup and view all the answers

What is the final test to confirm the presence of Cl- after I- and Br- have been removed?

Adding dilute HNO3 and observing for white precipitate. Signup and view all the answers

Study Notes

Solubility Product

The solubility product (Ksp) is a constant that describes the equilibrium between a solid ionic compound and its ions in a saturated solution.
The Ksp value for AgCl is 1 x 10^-10, meaning the product of the concentrations of Ag+ and Cl- ions in a saturated solution is 1 x 10^-10.
The Ksp value can be used to predict if a solution is saturated, supersaturated, or unsaturated.

Common Ion Effect

The common ion effect describes the suppression of the ionization of a weak electrolyte when a strong electrolyte containing a common ion is added to the solution.
For example, adding HCl to a solution of H2S will suppress the ionization of H2S because of the common ion Cl-.
The common ion effect can be used to control the solubility of ionic compounds.

Separation of Cations into Groups

Cations can be separated into groups based on their tendency to form precipitates with specific group reagents.
The group reagents used include HCl, H2S, (NH4)2Sx, NH4OH, and (NH4)2CO3.
The table shows the separation of cations into groups:

Group No. | Group Reagent | Cations Precipitated

------ | -------- | -------- I | HCl | Pb2+, Hg2+, Ag+ II | H2S (in acidic solution) | Cu2+, Cd2+, Hg2+, Pb2+, Bi3+, As3+, As5+, Sb3+, Sb5+, Sn2+, Sn4+ III | H2S (in alkaline solution) | Ni2+, Co2+, Mn2+, Zn2+, Fe2+, Fe3+ IV | (NH4)2CO3 | Ca2+, Sr2+, Ba2+ V | (NH4)2HPO4 | Mg2+

Applications of Complex Formation

Complex formation plays a pivotal role in qualitative analysis and various separations.
The separation of the IIA and IIB groups involves the formation of soluble thio-complexes like ammonium thioantimonite, thioarsinite, thioantimonate, thioarsenate, and thiostannate.
The separation of Cu2+ from Cd2+ utilizes the formation of the stable tetracyanocopper(II) complex [Cu(CN)4]3-, while Cd2+ forms a less stable complex [Cd(CN)4]2-.

Separation of Co2+ from Ni2+

The separation of cobalt(II) from nickel(II) involves converting them into their chloride forms and treating them with amyl alcohol and ammonium thiocyanate.

Detection of NO2- and NO3- (Brown Ring Test)

The brown ring test is a classic method for the detection of nitrite and nitrate ions.
The brown ring is formed by the reaction of NO with Fe2+ ions to form the [FeNO]SO4 complex.
The test must be carried out in the absence of bromide and iodide ions as these ions too form colored complexes with Fe2+.

Applications of Oxidation-Reduction

Oxidation-reduction reactions play a major role in qualitative analysis for detecting and confirming the presence of various ions.
One example is the separation of chloride, bromide, and iodide using potassium persulfate (K2S2O8) or chlorine water.
The strong oxidizing agents, K2S2O8 and chlorine water, oxidize the halides, sequentially, to their elemental forms, enabling their detection and removal.
The separation of different halides is achieved by selectively oxidizing them.
The detection of chloride ions is confirmed by the formation of white silver chloride precipitate, which dissolves in ammonia and reappears with dilute nitric acid.

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Description

This quiz covers key concepts in solubility product (Ksp), the common ion effect, and the separation of cations into groups based on their reactivity. Understand the implications of Ksp values on solution saturation and the impact of common ions on ionization. Test your mastery of these fundamental chemistry principles.