Some important compounds of Transition Metals: We contact transition metals daily without even realising it. Consider the element iron. Iron is used in a variety of applications, including ships, buildings, and cutlery. Some important transition element compounds are also used in similar ways in our daily lives. So, read the article below to learn more about important transition metal compounds.

Transition Elements

The transition elements may be defined as the elements whose atoms or simple ions contain partially filled d-orbitals. The d-block elements in groups of \(3\) to \(11\) are known as transition elements. Inner transition metals, including the lanthanides and actinides, are another name for the f block elements. 

Transition metals react with non-metals such as oxygen, nitrogen, phosphorus, halogens, sulphur, and carbon to form binary compounds. Some of these compounds are extremely important in the industry. Following are some important compounds of Transition metals.

Oxides and Oxoanions of Metals

The elements of the first transition series combine to form a variety of oxides with various oxidation states, with general formulae \(\mathrm{MO}, \mathrm{M}_{2} \mathrm{O}_{3}, \mathrm{M}_{3} \mathrm{O}_{6}, \mathrm{MO}_{2}, \mathrm{MO}_{3}\). In most cases, these oxides are formed by heating the metal with oxygen at a high temperature. These oxides have been listed in the table below:

\(\text {Sc}\)	\(\mathrm{Sc}_{2} \mathrm{O}_{3}\) (basic)
\(\text {Ti}\)	\(\mathrm{TiO}\) (basic), \(\mathrm{Ti}_{2} \mathrm{O}_{3}\) (basic), \(\mathrm{TiO}_{2}\)(amphoteric)
\(\text {V}\)	\(\mathrm{VO}\)(basic), \(\mathrm{V}_{2} \mathrm{O}_{3}\) (basic), \(\mathrm{VO}_{2}\)(amphoteric), \(\mathrm{V}_{2} \mathrm{O}_{5}\)(acidic)
\(\text {Cr}\)	\(\mathrm{CrO}\)(basic), \(\mathrm{Cr}_{2} \mathrm{O}_{3}\)(amphoteric), \(\mathrm{CrO}_{2}\)(amphoteric), \(\mathrm{CrO}_{3}\)(acidic)
\(\text {Mn}\)	\(\mathrm{MnO}\)(basic), \(\mathrm{Mn}_{2} \mathrm{O}_{3}\)(basic), \(\mathrm{Mn}_{3} \mathrm{O}_{4}\)(amphoteric), \(\mathrm{MnO}_{2}\)(amphoteric), \(\mathrm{Mn}_{2} \mathrm{O}_{7}\)(acidic)
\(\text {Fe}\)	\(\mathrm{FeO}\)(basic), \(\mathrm{Fe}_{2} \mathrm{O}_{3}\)(amphoteric), \(\mathrm{Fe}_{3} \mathrm{O}_{4}\)(basic)
\(\text {Co}\)	\(\mathrm{CoO}\)(basic)
\(\text {Ni}\)	\(\mathrm{NiO}\)(basic)
\(\text {Cu}\)	\(\mathrm{Cu}_{2} \mathrm{O}\)(basic), \(\mathrm{CuO}\)(amphoteric)
\(\text {Zn}\)	\(\mathrm{ZnO}\)(amphoteric)

Except for scandium, all metals form \(\text {MO}\) oxides, which are ionic in nature. The metal’s highest oxidation number in the oxides coincides with the group number and is attained in the case of metals ranging from scandium to manganese \(\left(\mathrm{SC}_{2} \mathrm{O}_{3}\right.\) to \(\left.\mathrm{Mn}_{2} \mathrm{O}_{7}\right)\). Except for \(\mathrm{Fe}_{2} \mathrm{O}_{3}\), no higher oxides are known beyond group-\(7\).

In addition to oxides, oxocations stabilise \(\mathrm{V}(\mathrm{V})\) as \(\mathrm{VO}_{2}^{+}, \mathrm{V}(\mathrm{IV})\) as \(\mathrm{VO}^{2+}\), and \(\text {Ti} (\mathrm{IV})\) as \(\mathrm{TiO}^{2+}\). These oxides exhibit acidic, basic and amphoteric behaviour.

Some of the characteristic features of these oxides are given below:

1. Oxides are generally basic when the metal is in a lower oxidation state and acidic when the metal is in a higher oxidation state. 
2. If the metal is in an intermediate oxidation state, the oxides are generally amphoteric.

For example, \(\text {Mn}\) oxides exhibit the following behaviour:

Similarly, \(\mathrm{CrO}\) is basic, \(\mathrm{Cr}_{2} \mathrm{O}_{3}\) is amphoteric, and \(\mathrm{CrO}_{3}\) is acidic in the case of chromium. When it comes to vanadium, \(\mathrm{V}_{2} \mathrm{O}_{3}\) is basic, \(\mathrm{V}_{2} \mathrm{O}_{4}\) is less basic, and \(\mathrm{V}_{2} \mathrm{O}_{5}\) is amphoteric (predominantly acidic). \(\mathrm{V}_{2} \mathrm{O}_{4}\) dissolves in acids to form \(\mathrm{VO}^{2+}\) salts. \(\mathrm{V}_{2} \mathrm{O}_{5}\) reacts with alkalis to produce \(\mathrm{VO}_{4}{ }^{3-}\) salts and acids to produce \(\mathrm{VO}_{4}{ }^{+}\) salts.

Potassium Dichromate \(\left(\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}\right)\)

Chromite ore \(\left(\mathrm{FeCr}_{2} \mathrm{O}_{4}\right)\) is used to make potassium dichromate. The following are the various steps involved:

1. Preparation of sodium chromate: In a reverberatory furnace, powdered ore is heated with molten alkali in the presence of air to produce sodium chromate.

2. Conversion of sodium chromate into sodium dichromate: To make sodium dichromate, sodium chromate is extracted with water and acidified with sulphuric acid. On cooling, sodium sulphate separates as \({\rm{N}}{{\rm{a}}_2}{\rm{S}}{{\rm{O}}_4} \cdot 10{{\rm{H}}_2}{\rm{O}}\), and the solution contains sodium dichromate. Orange \(\mathrm{Na}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7} .2 \mathrm{H}_{2} \mathrm{O}\) crystallises from this solution.

3. Conversion of sodium dichromate into potassium dichromate: Sodium chloride, the least soluble, separates out and is removed by filtration. When potassium dichromate cools, it crystallises into orange crystals. Potassium dichromate dissolves fairly well in water.

Properties of Potassium Dichromate

i. It has a melting point of \(671 \mathrm{~K}\) and is an orange crystalline solid.
ii. It is highly soluble in hot water but only moderately so in cold water.
iii. The action of heat: \(\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}\) decomposes on heating to form potassium chromate and chromic oxide.

iv. It acts as a strong oxidising agent in an acidic medium.

It oxidises sulphites to sulphates, chlorides to chlorine, nitrites to nitrates, thiosulphates to sulphates and sulphur, and stannous salts \(\left(\mathrm{Sn}^{2+}\right)\) to stannic salts \(\left(\mathrm{Sn}^{4+}\right)\)
The chemical equations are as follows:

v. Reaction with hydrogen peroxide: Acidified solution of dichromate ions forms a deep blue colour with hydrogen peroxide due to the formation of \(\mathrm{CrO}_{5}\).

Uses of Potassium Dichromate

1. In photography, it is used to harden gelatine film.
2. In dyeing, for use as a mordant.
3. \(\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}\) and conc. \(\mathrm{H}_{2} \mathrm{SO}_{4}\) make up the chromic acid mixture used to clean glassware.
4. In the leather industry, potassium dichromate is used in chrome tanning.
5. It is employed as an oxidising agent.
6. For the volumetric estimation of ferrous salts, iodides and sulphites.
7. For the preparation of other chromium compounds such as chrome alum, \(\mathrm{K}_{2} \mathrm{SO}_{4} \mathrm{Cr}_{2}\left(\mathrm{SO}_{4}\right)_{3} \cdot 24 \mathrm{H}_{2} \mathrm{O}\), chrome yellow \(\left(\mathrm{PbCrO}_{4}\right)\) and chrome red \(\left(\mathrm{PbCrO}_{4} \mathrm{PbO}\right)\).

Potassium Permanganate

Pyrolusite is used to make potassium permanganate \(\left(\mathrm{KMnO}_{4}\right)\). In the presence of atmospheric oxygen or an oxidising agent such as potassium nitrate or potassium chlorate, pyrolusite is fused with \(\text {KOH}\) to form potassium manganate, \(\mathrm{K}_{2} \mathrm{MnO}_{4}\).

The green mass is extracted with water and oxidised to potassium permanganate, either electrolytically or by passing chlorine or ozone through the solution.

Oxidation by Electrolysis

At the anode, manganate ions are oxidised to permanganate: 

At cathode, 

Oxidation by Chlorine:

The green colour of the solution changes to purple as a result of oxidation. The purple solution containing \(\mathrm{KMnO}_{4}\) is concentrated by evaporation, which results in the formation of \(\mathrm{KMnO}_{4}\) crystals upon cooling.

Properties of Potassium Permanganate

i. Potassium permanganate is a violet crystalline solid with a melting point of \(513 \mathrm{~K}\).
ii. It is water-soluble, and its aqueous solution is purple in colour.
iii. Effect of alkaline solution: In an alkaline solution, \(\mathrm{KMnO}_{4}\) is first reduced to manganate and then to insoluble manganese dioxide
iv. Effect of heat: When heated, potassium permanganate transforms into manganate, and oxygen gas is evolved.

v. Effect of Alkalis: When potassium permanganate is heated with alkalis, it transforms into manganate and evolves into oxygen gas.

vi. Oxidising Properties: In acidic, neutral, and alkaline media, KMnO₄ is a very powerful oxidising agent. The following equations represent oxidation in these media:

In acidic medium,

In neutral or alkaline medium,

Uses of Potassium Permanganate

1. In the laboratory and industry, it is used as an oxidising agent.
2. It is used for volumetric estimation of ferrous salts, oxalates and other reducing agents. 
3. It is used to detect halides, oxalates, tartrates, and sulphites, etc.
4. It is used as a water disinfectant.
5. It is employed in dry cells.
6. It is employed in the bleaching of wool, cotton, silk, and other textile fibres.

Summary

The transition elements may be defined as the elements whose atoms or simple ions contain partially filled d-orbitals. The elements of the first transition series combine to form a variety of oxides with various oxidation states.

Chromite ore \(\left(\mathrm{FeCr})_{2} \mathrm{O}_{4}\right)\) is used to make potassium dichromate \(\left(\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}\right)\), and Pyrolusite is used to make potassium permanganate \(\left(\mathrm{KMnO}_{4}\right)\). These have many applications, such as these are used in the laboratory and industry as an oxidising agent; in the leather industry, potassium dichromate is used in chrome tanning, potassium permanganate is used in dry cells, and also bleaching of wool, cotton, silk, etc.

FAQs on Some Important Compounds of Transition Metals

Q.1. What are some important compounds of transition metals?
Ans: Some important compounds of transition metals are potassium dichromate and potassium permanganate.

Q.2. What type of compounds do transition metals have?
Ans: Bonding in transition element simple compounds ranges from ionic to covalent.

Q.3. Which is the most important transition metal?
Ans: Iron is the most important transition metal.

Q.4. What are the main transition metals?
Ans: The main transition metals are Scandium, Titanium, Vanadium, Chromium, Manganese, Iron, Cobalt, Nickel, copper, zinc, etc.

Q.5. What is special about the compounds of transition metals?
Ans: The presence of unpaired electrons in the partially filled d-shell, which gives rise to magnetic properties, is one of the distinguishing properties of transition-metal compounds.

Q.6. What do you mean by the stability of coordination compounds?
Ans: The degree of association between the metal ion and the ligands involved in the state of equilibrium is the stability of coordination compounds in the solution.

Learn About Classification Of Elements Here

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