Among PbS, CuS, HgS, MnS, Ag2S, NiS, CoS, Bi2S3, and SnS2 the total number of BLACK coloured sulphid

Q: Why is MnS pink while other Group IV sulphides are black?

The color of transition metal compounds depends heavily on d-d transitions and charge transfer spectra. $Mn^{2+}$ has a high-spin $d^5$ configuration, making its d-d transitions both spin-forbidden and Laporte-forbidden. This results in a very pale, buff/pink color, unlike the intense black charge-transfer colors of NiS and CoS.

Q: Is Bi2S3 considered black or brown?

It is technically brown or brownish-black. In the context of this specific JEE question, the ambiguity was acknowledged, and both 6 (excluding Bi2S3) and 7 (including Bi2S3) were awarded full marks.

Q: How can I memorize all these colors efficiently?

Group them logically! Most Group II sulphides (CuS, PbS, HgS) are black. Group IV has black (NiS, CoS) and white/pink (ZnS, MnS). Exceptions like CdS (yellow) and SnS2 (yellow) are much easier to remember when isolated from the 'black' majority.

Q: Does the medium (acidic vs basic) affect the color of the precipitate?

The medium (pH) affects the *solubility* and whether the precipitate forms at all (due to the common ion effect on $S^{2-}$ concentration), but the intrinsic color of the solid sulphide remains the same once it has formed.

Q: What is the color of Ag2S?

Ag2S is a black precipitate. It is the exact same chemical compound that forms when silver jewelry tarnishes in the presence of sulfur compounds in the air.

Question

Among PbS, CuS, HgS, MnS, Ag2S, NiS, CoS, Bi2S3 , and SnS2 the total number of BLACK coloured sulphides is

Sigma Percentile · Accepted Answer

### The Colorful World of Qualitative Analysis

In the fascinating realm of qualitative salt analysis, the precipitation of metal sulphides is one of the most reliable methods for identifying cations. When hydrogen sulphide gas is passed through a solution containing various metal ions, they precipitate out as solid sulphides.

The beauty of this process lies in the distinct colors these precipitates exhibit. For a JEE aspirant, memorizing these colors is not just about rote learning; it is about recognizing the chemical signatures of different transition and post-transition metals.

### Grouping the Black Sulphides

Let's systematically break down the list provided in the question. We start by looking at the classic Group I and Group II cations. Lead ($Pb^{2+}$), Copper ($Cu^{2+}$), Mercury ($Hg^{2+}$), and Silver ($Ag^+$) are notorious for forming highly insoluble, pitch-black precipitates when reacted with sulphide ions.

Thus, we immediately identify $\mathrm{PbS}$, $\mathrm{CuS}$, $\mathrm{HgS}$, and $\mathrm{Ag_2S}$ as strictly black.

Moving on to Group IV, the precipitation occurs in a basic medium. Here, Nickel ($Ni^{2+}$) and Cobalt ($Co^{2+}$) also form distinctly black sulphides. This adds $\mathrm{NiS}$ and $\mathrm{CoS}$ to our growing list, bringing our count of undeniably black precipitates to six.

### The Exceptions: Pink, Yellow, and Brown

Not all sulphides are black, and these exceptions are high-yield facts for competitive exams. Manganese sulphide ($\mathrm{MnS}$) is a classic outlier in Group IV, precipitating with a unique dirty pink or buff color.

Similarly, Tin(IV) sulphide ($\mathrm{SnS_2}$) stands out with a bright, unmistakable yellow color.

This leaves us with Bismuth sulphide ($\mathrm{Bi_2S_3}$). In laboratory settings, $\mathrm{Bi_2S_3}$ is typically observed as a dark brown or brownish-black precipitate. Because it straddles the line between brown and black, it introduces a slight ambiguity.

### The Final Verdict

Due to the brownish-black nature of $\mathrm{Bi_2S_3}$, the official JEE Advanced answer key generously accepted both **6** and **7** as correct answers.

However, if we strictly count the purely black sulphides, we have exactly six: **$\mathrm{PbS}$, $\mathrm{CuS}$, $\mathrm{HgS}$, $\mathrm{Ag_2S}$, $\mathrm{NiS}$, and $\mathrm{CoS}$**. Mastering these color associations is a surefire way to secure quick marks in inorganic chemistry!

Animated Solution for Chemistry - Salt Analysis: Among PbS, CuS, HgS, MnS, Ag2S, NiS, CoS, Bi2S3 , and SnS2 the total number of BLACK coloured sulphides is

Enter Numerical Value:

Visualized Solution

\text{List of Sulphides}

\text{Black Sulphides (Group I \& II)}

\text{Black Sulphides (Group IV)}

\text{Non-Black Sulphides}

\text{The Case of } \mathrm{Bi_2S_3}

\text{Total Black Sulphides} = 6

The Sigma Insight: Salt Analysis

The Colorful World of Qualitative Analysis

Grouping the Black Sulphides

The Exceptions

The Final Verdict

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