Question

Mark the correct statement. (a) V group basic radicals precipitate as carbonates (b) IV group basic radicals precipitate as sulphides (c) I group basic radicals precipitate as chlorides (d) all the above statements are correct

Short answer

All statements are correct; option (d) is the answer.

Step-by-step solution

Understanding Group Precipitation

In qualitative analysis, basic radicals (cations) are categorized into groups based on their precipitation behavior with certain reagents. Each group is defined by the specific reagent that precipitates most of the cations within the group.

Examining Group I

Group I cations (basic radicals), such as Ag⁺, Pb²⁺, and Hg₂²⁺, are precipitated by the addition of dilute hydrochloric acid (HCl) as chlorides. Thus, statement (c) is correct.

Checking Group IV

Group IV cations precipitate as sulphides when exposed to hydrogen sulphide (H₂S) in an acidic medium. This means that statement (b) accurately describes Group IV precipitation conditions.

Inspecting Group V

For Group V cations, precipitation occurs as carbonates when treated with ammonium carbonate ( ext{(NH₄)₂CO₃}) in the presence of ammonia (NH₃). Therefore, statement (a) is correct about Group V precipitation.

Concluding the Solution

Since we verified that all three group precipitation statements are accurate based on standard qualitative analysis procedures, it follows that the correct option is (d) 'all the above statements are correct.'

Key concepts

Basic Radicals

In the realm of qualitative analysis, basic radicals are synonymous with cations, which are positively charged ions. These cations are pivotal in identifying substances through various chemical tests. The term 'basic radical' not only emphasizes the positive charge but also highlights the role they play as the 'basic' part of salts. Understanding them is fundamental in chemistry, particularly in the analysis of substances.

To systematically identify basic radicals, chemists divide them into different groups. These groups are based on the distinct chemical reactions these cations undergo. By observing how these radicals respond to specific reagents, chemists can deduce the presence of particular elements. Recognizing basic radicals involves identifying their properties and knowing the key reactions they participate in. With such identification, the fundamental chemical nature of an unknown compound can be discovered, aiding in thorough qualitative analysis.

Cation Precipitation

Cation precipitation is a vital process in the qualitative analysis, where particular reagents cause the cation to separate from a solution as a solid. This reaction helps to isolate specific ions, making it easier to identify them. Cation precipitation occurs because the product (a precipitate) formed is less soluble in the solution.

To understand this better, consider how Group I cations such as Ag⁺, Pb²⁺, and Hg₂²⁺ react with dilute HCl to form chlorides. The reaction equation can be expressed as:\[ \text{Ag}^{+} + \text{Cl}^{-} \rightarrow \text{AgCl} \ (\text{solid}) \]This reaction indicates a strongly visible precipitate of silver chloride, which aids in identifying these ions.

The practice of causing cation precipitation allows chemists to systematically rule out or confirm the presence of specific elements, based on the specific precipitate formed under predefined conditions.

Group Analysis

Group analysis is a systematic approach used to identify cations in a mixture. In qualitative chemical analysis, cations are grouped based on their reactions with certain reagents that cause precipitation. This stepwise grouping helps in the comprehensive identification of various ions present in a complex mixture.

The groups range from I to V (or more, depending on the scheme). For instance, Group I consists of cations that precipitate as chlorides when treated with hydrochloric acid, like silver (Ag⁺), lead (Pb²⁺), and mercury (Hg₂²⁺).

• Group I: Cations precipitate as chlorides.
• Group IV: Cations precipitate as sulphides in acidic medium.
• Group V: Cations precipitate as carbonates when treated with ammonium carbonate.

By sequentially adding specific reagents and observing the formation of precipitates, chemists can isolate and identify individual ions. Group analysis thus provides structure and clarity when working to deduce the nature of the components in a sample by eliminating subsets systematically.

Chemical Precipitation Reactions

Chemical precipitation reactions are reactions where a solid, referred to as a precipitate, forms and separates from a solution. This phenomenon is key in qualitative analysis for separating and identifying ions in a solution.

For example, in Group IV analysis, the addition of hydrogen sulphide in an acidic medium causes Group IV cations to form sulphide precipitates. The reaction mechanism is straightforward:\[ \text{Metal}^{2+} + \text{H}_2\text{S} \longrightarrow \text{MetalS} \ ( ext{solid}) + 2\text{H}^+ \]Here, the precipitate (sulfide ion) reveals the presence of specific metal cations. Chemists observe the color and nature of the precipitate to help identify the cations.

• Precipitation reactions are essential for isolating ions from a solution.
• These reactions are influenced by factors like pH and reagent concentration.

Chemical precipitation reactions form the foundation of many traditional qualitative analyses by offering a clear path to identifying unknown ions based on the insoluble product formed.