Home
Class 12
CHEMISTRY
In qualitative analysis, to identily the...

In qualitative analysis, to identily the HA group sulphides, HCl is added to salt solution before the addition of `H_(2)S`. Because

A

Low `S^(2-)` ion concentration is required to get ppt

B

High `S^(2-)` ion concentration is required to get ppt

C

A group metal sulphides have higher values of `K_(sp)` than that of IVA group metal sulphides

D

`p^(H)` value increases

Text Solution

AI Generated Solution

The correct Answer is:
To solve the question regarding the addition of HCl to the salt solution before adding H₂S in the qualitative analysis of HA group sulfides, we can follow these steps: ### Step-by-Step Solution: 1. **Understanding the Context**: In qualitative analysis, we often need to identify specific groups of ions in a solution. The HA group refers to a specific set of cations that can form sulfide precipitates. 2. **Role of HCl**: When HCl is added to the salt solution, it provides a source of H⁺ ions. This is crucial because it helps to maintain an acidic environment in the solution. 3. **Adding H₂S**: H₂S (hydrogen sulfide) is then introduced to the solution. H₂S can dissociate in water to produce H⁺ and S²⁻ ions. 4. **Common Ion Effect**: The presence of H⁺ ions from HCl suppresses the ionization of H₂S. This is known as the common ion effect, where the addition of a common ion (H⁺ in this case) reduces the solubility of a salt (H₂S) in solution. 5. **Lower Sulfide Ion Concentration**: Due to the common ion effect, the concentration of sulfide ions (S²⁻) in the solution is lowered. This is important because a lower concentration of sulfide ions is necessary to selectively precipitate the sulfides of the HA group cations. 6. **Precipitation of Sulfides**: Only when the concentration of sulfide ions is sufficiently low can the specific sulfides of the HA group cations precipitate out of the solution. If the concentration were too high, other sulfides might precipitate, making it difficult to identify the HA group. 7. **Conclusion**: Therefore, HCl is added before H₂S to ensure that the ionization of H₂S is suppressed, resulting in a lower concentration of sulfide ions, which is essential for the selective precipitation of HA group sulfides. ### Final Answer: HCl is added to the salt solution before the addition of H₂S to suppress the ionization of H₂S due to the common ion effect, resulting in a lower concentration of sulfide ions necessary for the precipitation of HA group sulfides. ---
Promotional Banner

Similar Questions

Explore conceptually related problems

A black sulphide is formed by the action of H_(2)S on

A black sulphide is formed by the action of H_(2)S on:

In salt analysis. Explain why NH_4Cl is added before the addition of NH_4OH in group III.

To precipitate group III cations NH_4Cl should be added to the solution before the addition of ammonium hydroxide. Explain why. ""^(**"**)

In the group II of qualitative analysis, It is necessary to pass H_2S in …………. Medium , otherwise the sulphides of the cations of group ……… will also get precipitated.

In qualitative analysis when H_(2)S is passed through an aqueous solution of salt acidified with dil. HCL, a block precipitate is obtainned .On boiling the precipitate with dil. HNO_(3) it forms a solution of blue colour . Addition of excess of aqueous solution of ammonia to this solution given ....... .

In qualitative analysis when H_(2)S is passed through an aqueous solution of salt acidified with dil. HCl, a black precipitate is obtained. On boiling the precipitate with dil. HNO_(3) , it forms a solution of blue colour. Addition of excess of aqueous solution of ammonia to this solution gives

In qualitative analysis, when H_2S is passed through an aqueous solution of salt acidified with dil.HCl, a black precipitate is obtained. On boiling the precipitate with dil. HNO_3 , it forms a solution of blue colour. Addition of excess of aqueous solution of ammonia to this solution gives

In qualitative inorganic analysis of basic radicals hydrochloric acid is preferred to nitric acid for preparing a solution of given substance .This is because :

In equalitative analysis, cations of graph II as well as group IV both are precipitated in the form of sulphides. Due to low value of K_(sp) of group II sulphides, group reagent is H_(2)S in the presence of dil. HC1 , and due to high value of K_(sp) of group IV sulphides, group reagent is H_(2)S in the presence of NH_(4)OH and NH_(4)C1 . In a solution containing 0.1M each of Sn^(2+), Cd^(2+) , and Ni^(2+) ions, H_(2)S gas is passed. K_(sp) of SnS = 8 xx 10^(-29), K_(sp) of CdS = 15 10^(-28), K_(sp) of NiS - 3 xx 10^(-21), K_(1) of H_(2)S = 1 xx 10^(-7), K_(2) of H_(2)S = 1 xx 10^(-14) Which of the following sulphides is more soluble in pure water?