Identify halide ions - chloride, bromide, iodide

In this lesson, we are going to identify halide ions. chloride, bromide, iodide. We study what compounds are used to identify halide ions and what are the observations we can see after halide ions testing. Some halide ions compounds dissolve in water and some form precipitates. According to the physical state and halide ion, we choose different methods and reagents to test halide ion.


What is a halide ion?

Halide ion the anion of halogen atom. The charge of halide ion is -1. F-, Cl-, Br-, I- are the halide ions. These halide ions have some simialar properties and different properties.


All of those halides are in -1 oxidation state. Also these halides can be presence as solid state or solution state. Some of these halide compounds are precipitates. According to the state, we have to change the experimental method to identify the ion.


Identify halide ions in solution state

Here, we are going to discuss about 3 different methods to identify halide ions which exist such as NaCl(aq) , KI(aq) .

Identify chloride ion in solution state

  1. Add lead(ii) acetate ( Pb(CH3COO)2 ) or lead(ii) nitrate ( Pb(NO3)2 ). It will give white precipitate of lead(ii) chloride (PbCl2). Also this precipitate will melt in hot water and when it cools again, it will precipitate again.

    PbCl2 white precipitate colour
  2. Add first dilute HNO3 and then AgNO3(aq).
    It will give AgCl white precipitate which solve in dilute NH3.

    AgCl white precipitate identify Cl- ion

  3. Add CHCl3 or CCl4 and joggle the mixture.
    It will give colourless layer.



Identify bromide ion in solution state

  1. Add lead(ii) acetate ( Pb(CH3COO)2 ) or lead(ii) nitrate ( Pb(NO3)2 ). It will give white(cream) precipitate of lead(ii) bromide(PbBr2). Also this precipitate will melt in hot water and when it cools again, it will precipitate again.
    PbBr2 precipitate identify from hot water

  2. Add first dilute HNO3 and then AgNO3(aq).
    It will give AgBr light yellow precipitate which solve in conc. NH3.
    AgBr precipitate dissolve in concentrated ammonia

  3. Add CHCl3 or CCl4 and joggle the mixture.
    It will give brown/orange globule.

Identify iodide ion in solution state

  1. Add lead(ii) acetate ( Pb(CH3COO)2 ) or lead(ii) nitrate ( Pb(NO3)2 ). It will give yellow precipitate of lead(ii) bromide(PbI2). This precipitate will melt when it's boiling. Then cool the solution again, it will deposit as a gold yellow powder.
    PbI2 precipitate gold yellow colour powder

  2. Add first dilute HNO3 and then AgNO3(aq).
    It will give AgI yellow precipitate which doesn't solve NH3.
    AgI precipitate not dissolve in NH3

  3. Add CHCl3 or CCl4 and joggle the mixture.
    It will give purple globule.

identify chloride, bromide, iodide ions solutions


Identify halide ions in solid state

Here, we are going to discuss about 2 different methods to identify halides which exist as solids such as NaCl(s), KI(s)

Identify chloride ion in solid state compounds


Concentrated sulphuric acid and solid chloride then heat the mixture.

It will give NaHSO4 and HCl gas. HCl can be identified by ammonia (NH3) gas. HCl and NH3 reacts and give white solid fog of ammonium chloride(NH4Cl).
NaCl and concentrated sulfuric acid reaction

Concentrated sulphuric acid, MnO2 and solid chloride compound , then heat the mixture.

Manganese dioxide(MnO2) is a oxidizing agent which oxidizes chloride ions into chlorine gas. Light yellow green colour Cl2 gas is released in the reaction.Cl2is a toxic gas.
MnO2 + NaCl +H2SO4


Chromyl Chloride Test to identify chloride ion

Add K2Cr2O7, concentrated H2SO4 to solid chloride. Then heat the mixture. A red colour vapour CrO2Cl2 is formed.

Chromyl Chloride Test to identify chloride ion

Add NaOH. CrO2Cl2 and OH- react to give yellow solution CrO42-. Then add CH3COOH and Pb(CH3COO)2. A yellow colour PbCrO4 precipitated is formed. PbCrO4(s) solve in dilute HNO3.

chromate ion and dichromate ion HNO3 acid

Identify bromide ion - solid state compounds


Concentrated sulphuric acid and solid bromide compounds then supply heat to the mixture

It will give brown colour Br2 gas. H2 gas also is given.

NaBr + H2SO4 gives Br2

NaCl(s) gives HBr with concentrated H3PO4.

When hot concentrated H3PO4 acid is added to solid NaCl, HBr vapour is formed.



Concentrated sulphuric, MnO2 with solid bromide compounds, then heat the mixture.

It will give brown colour Br2 gas. MnO2 is reduced to Mn2+ ions.


Identify iodide ion in solid state compounds


Concentrated sulphuric acid and solid iodide compound, then heat the mixture.

Iodide ion is oxidized and it will give purple colour I2 gas. Also hydrogen gas is given.


Concentrated sulphuric acid, MnO2 and solid iodide compound then heat the mixture.

It will give purple colour I2 gas.


KI and H3PO4

HI is formed. H3PO4 is not a oxidizing acid.

KI + H3PO4

KI(s), K2Cr2O7 and H2SO4(aq) reaction

Purple colour I2 is given. Also Cr3+ is formed. But red CrO2Cl2 vapour is not given.

KI + H2SO4 + K2Cr2O7

Iodide ion and Cu2+ or Fe3+ reaction

I2 is released. I2 can be identified by farina.

Iodide ion and Cu2+ or Fe3+ reaction



identify cloride, bromide, iodide ions solid compounds


Halide ions of alkali metals

All alkali metal halide compounds are high melting crystalline solids. All alkali metal halide compounds are soluble in water exception of LiF. LiF is insoluble in water due to its high lattice energy because of small cation and small anion size. Other halide ions of lithium are soluble in ethanol, acetone, ethyl acetate. LiCl is soluble in pyridine. CsI has also low solubility due to smaller hydration energy of its two ions.



Halide ions of alkali earth metals

Being covalent BeCl2 is soluble in organic solvents. MgCl2, MgBr2 are soluble in organic solvents. BeCl2 has low melting point and BaCl2 has higher melting points. Fluorides of alkali earth metals are sparingly soluble in water. The solubility increases slightly with increase of cation size. All alkali earth metals are ionic and soluble in water except BeCl2.



Colours of halide compounds

Some halide compounds have colours. Below all compounds are precipitates.

  • PbCl2(s) : white
  • PbBr2(s) : white cream
  • PbI2(s) : yellow
  • AgCl2(s) : white
  • AgBr2(s) : light yellow
  • PbI2(s) : yellow

Hydrogen halides

Hydrogen halides are the most useful compounds of halogens. HCl, HBr, HI are strong acids and HF is a weak acid. All of the hydrogen halides are very soluble in water. HCl, HBr, HI are almost completely dissociated in dilute solutions.

Preparing hydrogen halides

Heating a salt containing the halide ion with a nonvolatile acid is the usual way in which HF, HCl, and HBr are obtained in laboratory experiments.


Preparing HCl, HBr and HI

Preparing HF

But this method cannot use to prepare HI because HI is not relatively stable than other hydrogen halides.

Preparing HI

prepare a compound containing iodine,then carry out a hydrolysis reaction.

Hydrolysis iodine compound to prepare HI



Questions of halide ions


How do you identify sodium chloride and sodium bromide solution?

There are two colourless aqueous solutions without labels. But students have been informed that those two solutions are sodium chloride and sodium bromide. You are advised that. Propose a method to identify these two solutions.


Sodium ion is common in two solutions. So we have to do the testing for chloride ions and bromide ion.

First add dilute nitric acid and then lead nitrate solution. You can notice that a white precipitate and light yellow precipitate form in two solutions. White precipitate is lead chloride. Now we can identify two solutions from comparing colours of two precipitates.



How do you identify sodium nitrite and sodium bromide?

Both sodium bromide and sodium nitrite are white solid compounds at room temperature.

  • Add both solids to water separately to see a difference. No you cannot see a change. Both compounds give colourless solutions. So what to do next?
  • Add aqueous silver nitrate to colourless solutions. In one flask, a white precipitate is formed.
  • Consider existing anions and cations of two solutions.
  • In Sodium bromide solution, Na+, Br-, Ag+, NO3-
  • In sodium nitrite, Na+, NO2-, Ag+, NO3-
When Ag+ and Br- ions are in the solution, it give AgBr white precipitate.

How to test chloride ion in presence of bromide ion?

We can do concentrated sulfuric acid and manganeese dioxide to test chloride ion in the presence of bromide ion. Here how it does.

Manganeese dioxide - MnO2

Add concentrated sulfuric acid and heat the mixture. You can see a vapour of Br2 in red brown colour. Then again add concentrated sulfuric acid and MnO2. A yello green Cl2 gas emits.


What are the coloured solutions when add concentrated excess aqueous HCl to transition metal ions?

When we add concentrated excess aqueous HCl to transition metal ions, complexes or coordination compounds are formed. Some 3d metal ions give coloured solutions with concentrated excess aqueous Cl- ions.

3d metal ion complexes when add concentrated excess aqueous Cl- ions

  • [FeCl4]2-(aq) : yellow
  • [CoCl4]2-(aq) : blue
  • [NiCl4]2-(aq) : blue
  • [NiCl4]2-(ethanol) : yellow brown
  • [CuCl4]2-(aq) : yellow

How bromine and iodine are prepared by chlorine gas?

Chlorine is located under iodine and bromine in the electrochemistry series. Therefore reducing of chlorine(Cl2) to chloride(Cl-) is easier than Br2 to Br- and I2 to I-. Bromine is obtained by the oxidation of Br- with chlorine gas in saline water. Iodine is similarly produced by passing chlorine gas through saline water containing I- ions.
Cl2 + 2I- → I2 + 2Cl-
Cl2 + 2Br- → Br2 + 2Cl-


sodium bromide with copper presence of sulphuric acid

If you want to release bromine gas, you have to add concentrated sulfuric acid. If you use concentrated sulfuric acid in the presence of copper, copper is oxidized while sulfuric acid is reduced to sulfur dioxide because concentrated sulfuric acid is an oxidizing acid.


How to identify metal halides with potassium ions

All potassium halides ( KF, KCl, KBr, KI ) are soluble in water and give colourless solutions.

  • KF - white crystals, soluble in water and HF, but not soluble in alcohol.
  • KCl - White crystals, soluble in water, not souble in ethanol.
  • KBr - Colorless crystals or white granules or powder, soluble in water, Sparingly soluble in ethanol.
  • KI - white solid, soluble in water, Slightly soluble in ethanol.

Only KI is soluble in HF. And KBr and KI are sparingly soluble in ethanol.


Which halide ion, chloride, bromide and iodide is more easy to oxidize?

Iodide ion is easily oxidize to I2 than bromide to bromine and chloride to chlorine.


Lewis structures

P2O5 lewis structure OH- lewis structure Ammonium ion (NH4+) lewis structure H2CO3 lewis structure

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