Test for sulfide ion | Qualitative Analysis of S2- Anion

Sulfide ion forms compounds with cations. Some of them are soluble in water in water and metal sulfide compounds form precipitates. Specially, d block metal sulfides have colours which is used to identify the cation in such cases. However, alkali metal sulfides and alkali earth metal 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. In this tutorial, we will discuss followings in detail, how to identify sulfide anion.

  • Identify s block metal sulfides
  • Test for sulfide ion: Silver nitrate and aqueous sulfide solution
  • Sulfide anion with sodium nitroprusside solution
  • Sulfide anion with aqueous barium chloride solution | BaCl2
  • Test for Sulfide ion: Solid metal sulfide and a dilute acid
  • Insoluble sulfides in water
  • Identify s block metal sulfides

    There are two groups as alkali metals and alkali earth metals in s block. It's important to learn sulfides of those metal cations when identify sulfide compounds.

    S block metal sulfides in water

    Most of s block metal sulfides (except Strontium sulfide) are soluble in water and hydrolysis to alkaline aqueous colourless solutions releasing Hydrogen sulfide gas. Also, these s block metal sulfide emits Hydrogen sulfide gas when metal sulfides are hydrated. Therefore, you are unable to identify two s block metal sulfides by dissolving in water. As an example, you cannot see a colour when you dissolve sodium sulfide and potassium sulfide.

    s block metal sulfides at solid state

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

    Sulfides of alkali metal: colour, physical state and water solubility

    • Lithium sulfide (Li2S) : yellow-white deliquescent powder and readily hydrolysis to hydrogen sulfide.
    • Sodium sulfide (Na2S) : Has a rotten eggs smell. yellow-pink or white crystals
    • Potassium sulfide (K2S): Colourless, because of K2S readily reacts with water, it is rarely encounted in nature.
    • Rubidium sulfide (Rb2S): White solid

    Sulfides of alkali earth metals: colour, physical state and water solubility

    • Berrylium sulfide (Bes): White solid, in the presence of water, it decomposes.
    • Magnesium sulfide (MgS): White (in pure form) to reddish brown powder, MgS decomposes to Hydrogen sulfide gas and Magnesium hydroxide (Mg(OH2).
    • Calcium sulfide (CaS): White solid and hydrolysis to Hydrogen sulfide gas.
    • Strontium sulfide (SrS): White solid, slightly soluble in water
    • Barium sulfide (BaS): White solid and hydrolysis in water
  • Calcium sulfide (CaS) : White solid

  • Test for sulfide ion: 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

    Test for sulfide ion: With sodium nitroprusside solution

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

    sodium nitroprusside and sulfide ions

    Test for sulfide ion: with aqueous barium chloride solution | BaCl2

    Add aqueous Barium chloride to the aqueous sulfide ion solution. Barium sulfide (BaS) is a colourless solution and not a precipitate like Barium sulfate (BaSO4).

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

    Test for Sulfide ion: Solid metal sulfide and a dilute acid

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

    Insoluble sulfides of p block and 3d metals

    Most of 3d metal sulfide compounds and also some other p block metal sulfide compounds are insoluble in water and show different colours. Characteristics of such metal sulfides are explained in detail here.

    3d and p block insoluble metal sulfide compounds

    Following sulfide are precipitates and have specific colours. You have to remember those colours of precipitates when answering inorganic chemistry 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

    Because many metal sulfide compounds has the capability of releasing Hydrogen sulfide gas in a contact of water or moisture, it is importnat to know the several characteristics of Hydrogen sulfide gas.

    • 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.

    Commom questions and answers in test of sulfide ion

    Here, we are going to see how metal sulfide compounds are tested and identify them from other compounds.

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

    You may have observed that both Copper sulfide (CuS) and nickel sulfide (NiS) 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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