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.
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.
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.
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.
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
|Ferrous sulfide / Iron(II) sulfide
|Stannous sulfide / Tin(II) sulfide
||Yellow brown or dark brown
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
- 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
- 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.
Related tutorials for sulfide ion
3d metals colours, oxidation numbers, compounds