Testing Manganese ion | Qualitative Analysis of Mn2+

Manganese +2 ion is the most common ion of manganese in so many compounds of manganese such as manganese chloride, manganese sulfate and more. Aqueous manganese ion solution is light pink colour.

There are precipitates and soluble compounds for Mn2+ cation. They are important to identify compounds. In qualitative analysis, there are experiments to identify manganese 2+ ion from other cations.

In this tutorial, you will followings of Mn2+ ion

  1. Experiments to identify Mn2+ ion
  2. List of colours of manganese +2 ion compounds
  3. Solubility of Mn2+ ion's compounds

Experiments to test manganese +2 ion

Following experiments can be conducted to test Mn2+ ions. At the end of this tutorial, we do several exercises to testing Mn2+ ion to identify from other cations and compounds.

  1. Addition of aqueous sodium hydroxide (NaOH) to Mn2+ ion solution.
  2. Addition of hydrogen sulfide gas (H2S)
  3. Reaction of Mn2+, HNO3 and PbO2

Addition of aqueous sodium hydroxide (NaOH) to manganese 2+ ion solution

When aqueous NaOH solution is added to the Mn2+ ion solution, a buff white precipitate of manganese hydroxide ( Mn(OH)2 ) forms.

Mn2+ + 2NaOH → Mn(OH)2 + 2Na+

Manganese hydroxide is an insoluble hydroxide in water.

When manganese hydroxide is exposed to air or oxidizing agent like bromine water or sodium peroxide, manganese hydroxide is oxidized to manganese dioxide which is a black precipitate.

2Mn(OH)2 + O2 → 2MnO2 + 2H2O

In this process, oxidation number of manganese is increased from +2 to +4.

Addition of hydrogen sulfide gas (H2S) to aqueous Mn2+ ion solution

In a basic medium, hydrogen sulfide gas is sent to aqueous Mn2+ ion solution. A pink colour precipitate, manganese sulfide (MnS) is given.

Mn2+ + H2S → MnS + 2H+

Why basic medium is used to precipitate manganese sulfide?

To precipitate manganese sulfide, higher sulfide ion concentration is required. In basic medium, dissociation of hydrogen sulfide is shifted to right side and give higher S2+ concentration.

See other sulfide compounds which do not dissolve in water

Reaction of manganese +2 ion aqueous solution, HNO3 acid and PbO2

Boil a solution of Mn2+ with HNO3 acid and PbO2. Give sometime to settle pink / violet red colour of the supernatant liquid, due to formation of permanganic acid (HMnO4).

Mn2+ + 6HNO3 + 5PbO2 → 2HMnO4 + 3Pb(NO3)2 + 2Pb2+ + 2H2O

This is a redox reaction. Mn2+ ion is oxidized to HMnO4. As the reduction, PbO2 is reduced to Pb2+ ion.

Colours and solubility of Mn2+ compounds

Manganese hydroxide ( Mn(OH)2 )

A white precipitate which does not dissolve in water.

Manganese chloride solubility and colour

Manganese chloride is highly soluble in water. At solid state, manganese chloride exist as pink trigonal crystals. In the aqueous phase, it is colourless or yellow pink.

Manganese sulfate

In solid state, manganese sulfate exist as white crystals in anhydrous state. But in hydrate state, a pale pink colour is given by manganese sulfate.

Also MnSO4 is soluble in water like most metal sulfate compounds.

Manganese carbonate

Manganese carbonate is insoluble carbonate compound in water. In solid state it exists as white to faint pink soli.

Problems of testing Mn2+ ion to identify from other compounds

manganese 2+ ion colour

We can consider manganese 2+ ion colour in solid state and solution state. We will look about compounds of manganese 2+ ion.

Colour of manganese 2+ ion compounds in solid state

  • MnCO3: White to faint pink
  • MnS: Green to pinkish powder
  • MnSO4: pale pink
  • MnCl2: pink solid (tetrahydrate)

Colour of manganese 2+ ion compounds in solid state

  • MnSO4: pink
  • MnCl2: pink

You see, almost all compounds of manganese 2+ ion compounds are pink colour.

How do you identify Mn2+ ion and Zn2+ ion?

With H2S in the basic madium, Mn2+ ion solution gives a pale pink colour MnS precipitate.

With H2S in the basic madium, Zn2+ solution gives a white ZnS precipitate.

According to the colour of precipitatate, Mn2+ ion solution can be identified.

colour of manganese hydroxide?

Manganese hydroxide (Mn(OH)2) is insoluble in water and form a White precipitate in the water.

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