Testing sulfide ion | Qualitative Analysis of S2- ion

Sulfide ion forms compounds with cations. Some of them are dissolving in water , forms precipitates and have colours. s block sulfides are very much soluble in water. But 3d metal sulfides are insoluble in water and show colours when they form precipitates in the water.

inorganic chemistry, qualitative analysis, identify anions

S block metal sulfides

All s block metal sulfides (group IA, group IIA) are soluble in water and form colourless aqueous solutions.

s block metal sulfides at solid state

Here we are going to learn some s block sulfide compounds their characteristics.

  • Lithium sulfide (Li2S) : yellow-white deliquescent powder.
  • Sodium sulfide (Na2S) : Has a rotten eggs smell. yellow-pink or white crystals
  • Calcium sulfide (CaS) : White solid

Silver nitrate and aqueous sulfide solution

Add silver nitrate to aqueous sulfide solution. It gives black silver sulfide precipitate which is not soluble in dilute nitric acid. But it will dissolve in concentrated nitric acid.

silver and sulfide ion

With sodium nitroprusside solution

Add little bit NaOH to aqueous sulfide solution to make solution alkaline. Then add sodium nitroprusside ( Na2[Fe(CN)5(NO)] ) solution. You can see the purple colour.

sodium nitroprusside and sulfide ions

With aqueous barium chloride solution | BaCl2

Add aqueous barium chloride to the aqueous sulfide solution. BaS is a colourless solution and not a precipitate like BaSO4.

This reaction can be used to separate sulfide from and sulfate ions.

With dilute acids

Add dilute acid to a solid sulfide. Hydrogen sulfide acid (H2S) is produced which is an weak dibasic acid.

Insoluble sulfides

Most of 3d metal sulfide and some other p block metal sulfide are insoluble in water and show different colours.

3d and p block insoluble metal sulfide compounds

Following sulfide are precipitates and have colours. You have to remember those colours of precipitates to write answers in examinations.

Name of metal sulfide Chemical Formula Colour
Mercuric sulfide HgS Black
Antimony trisulfide Sb2S3 red-orange
Cadmium sulfide CdS yellow
Ferrous sulfide / Iron(II) sulfide FeS Black
Stannous sulfide / Tin(II) sulfide SnS Yellow brown or dark brown
Tin(IV) sulfide SnS2 yellow
Copper sulfide CuS Black
Copper sulfide CuS Black
Zinc sulfide ZnS White
Manganese sulfide MnS Pink
Nickel sulfide NiS Black
Cobalt sulfide CoS Black

Hydrogen sulfide | H2S

  • H2S has a characteristic smell of rotten eggs.
  • H2S can be identified by blackening of paper moistened with a solution of lead acetate Pb(CH3COO)2.
  • A very toxic gas. Inhaling in very low concentrations is enough to death.
  • Largely produced in petroleum refining as a impurity. But can be used to manufacture sulfuric acid.

How to identify copper sulfide and nickel sulfide? | CuS and NiS

You may have observed that both copper sulfide and nickel sulfide are black precipitates. Cations are different in compound. but anion, sulfide is common for both compounds. So we have to do the testing for cations to identify.

  • Add dilute HCl to both precipitates. You can see a gas is emitted in both cases because when a dilute acid is added to a metal sulfide hydrogen sulfide is released. Also in the aqueous solutions, copper chloride and nickel chloride compounds are produced.
  • Aqueous copper(ii) chloride solution is blue colour and aqueous nickel chloride is a green colour solution.
  • Accoring to the colour different, copper ion and nickel ion solutions can be identified and copper sulfide and nickel sulfide black precipitates too.

Propose a method to identify sulfide ion and sulfite ion

If sulfide ion solution and sulfite ion solution are as aqueous solutions, add barium chloride solution. You can see, in one flask, a white precipitate forms which is barium sulfite. But barium sulfide is a colourless solution.

Give chemical reactions which can identify zinc sulfide and zinc carbonate

Zinc sulfide and zinc carbonate are white solids at room temperature. Also both of them form white precipitates in the water. So we cannot identify zinc sulfide and zinc carbonate from dissolving.

  • Metal carbonates emit carbon dioxide when add a dilute acid. Metal sulfide emit hydrogen sulfide when add a dilute acid. Then we can test these two gases.
  • Send hydrogen sulfide and carbon dioxide gas to the two separate lead nitrate solutions.
  • With hydrogen sulfide, lead sulfide (a black precipitate) is given. With carbon dioxide, lead carbonate (a white precipitate) is given.
  • From that two different colour precipitates, we can identify two different gases and that also tells us which precipitates are zinc sulfide and zinc carbonate

Identify lead sulfide and lead sulfate

We are going to consider about insoluble compounds of sulfide and sulfate ions such as PbS or PbSO4. Add a dilute acid to the precipitates of lead sulfide and lead sulfate.

  • You can see, both precipitate will remain same. But in one solution, you can see a gas is emitted.
  • Sulfide will reacts with dilute HCl and produce hydrogen sulfide gas. You can do a test to identify hydrogen sulfide. The solution which emits the hydrogen sulfide gas is related to the lead sulfide.
  • Precipitates of sulfate ion does not dissolve in dilute acids.

chemical formula for nickel(ii) sulfide

NiS. Oxidation number of nickel (+2) is mentioned inside brackets.

sulfide ion testing

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