(b) What is the most significant difference between the sulfides precipitated in group 2 and those precipitated in group 3?

Name: Chemistry: The Central Science
Author: Brown
ISBN: 9780137542970

Verified step by step guidance

Identify the sulfides precipitated in Group 2: CuS, CdS, Bi2S3, PbS, HgS, As2S3, Sb2S3, SnS2.

Identify the sulfides precipitated in Group 3: ZnS, NiS, MnS, CoS.

Note that Group 2 sulfides are precipitated in acidic conditions (H2S and 0.2 M HCl).

Note that Group 3 sulfides are precipitated in basic conditions (NH4)2S at pH = 8.0.

The most significant difference is the pH condition under which the sulfides precipitate: Group 2 sulfides precipitate in acidic conditions, while Group 3 sulfides precipitate in basic conditions.

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Selective Precipitation

Selective precipitation is a technique used in analytical chemistry to separate ions in a solution based on their solubility. By adding specific reagents, certain ions will form insoluble compounds (precipitates) while others remain dissolved. This method is crucial for distinguishing between different groups of metal cations, as seen in the flowchart, which outlines the sequential addition of reagents to precipitate specific groups.

Group 2 vs. Group 3 Sulfides

The sulfides precipitated in Group 2 are primarily acid-insoluble, meaning they do not dissolve in acidic conditions, while those in Group 3 are base-insoluble, indicating they remain undissolved in basic conditions. This distinction is significant because it affects the conditions under which these sulfides can be separated and identified during qualitative analysis, as shown in the flowchart.

Precipitation Reagents

Precipitation reagents are chemicals added to a solution to induce the formation of a solid precipitate from dissolved ions. In the context of the flowchart, reagents like H2S and (NH4)2S are used to selectively precipitate sulfides from different groups of metal cations. Understanding the role of these reagents is essential for effectively separating and identifying metal ions in a mixture.

Recommended video:

Guided course

01:53

Selective Precipitation

Related Practice

Textbook Question

Rainwater is acidic because CO21g2 dissolves in the water, creating carbonic acid, H2CO3. If the rainwater is too acidic, it will react with limestone and seashells (which are principally made of calcium carbonate, CaCO3). Calculate the concentrations of carbonic acid, bicarbonate ion 1HCO3-2 and carbonate ion 1CO32 - 2 that are in a raindrop that has a pH of 5.60, assuming that the sum of all three species in the raindrop is 1.0 * 10-5 M.

789

views

Textbook Question

Suggest how the cations in each of the following solution mixtures can be separated: (c) Pb2 + and Al3 +.

465

views

Textbook Question

The acid–base indicator bromcresol green is a weak acid. The yellow acid and blue base forms of the indicator are present in equal concentrations in a solution when the pH is 4.68. What is the pKa for bromcresol green?

1392

views

Textbook Question

In the course of various qualitative analysis procedures, the following mixtures are encountered: (c) Mg²⁺ and K⁺ (d) Ag⁺ and Mn²⁺. Suggest how each mixture might be separated.

358

views

Textbook Question

A solution containing several metal ions is treated with dilute HCl; no precipitate forms. The pH is adjusted to about 1, and H₂S is bubbled through. Again, no precipitate forms. The pH of the solution is then adjusted to about 8. Again, H₂S is bubbled through. This time a precipitate forms. The filtrate from this solution is treated with (NH₄)₂HPO₄. No precipitate forms. Which of these metal cations are either possibly present or definitely absent: Al³⁺, Na⁺, Ag⁺, Mg²⁺?

696

views

rank