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Question
What are the chemical properties of Lanthanoids ?
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Solution
Chemical Properties of Lanthanides - The +3 lanthanide compounds are much more reactive than Aluminium compounds but slightly more reactive than Magnesium compounds (refer to the electrode potentials). They react slowly with cold water but rapidly with hot water.
- Hydroxides are precipitated by ammonia as gelatinous precipitates. They are less basic than Ca(OH)2 but more basic than Al(OH)3.
- Above 300-400°c lanthanides react with hydrogen to form solid hydrides. These hydrides have a non stoichiometric formula with 2H-ions while the metal is in +3 state. Yb forms approximately YbH2.5 hydride.
- Lanthanides tarnish readily in air, forming oxides. On heating with oxygen also they form the oxide M2O3. Ce is an exception and forms CeO2.
- Anhydrous halides are made by heating metal and halogen or alternatively, by heating oxide with the appropriate ammonium halide.
- Hydrated lanthanum chloride on heating dissociates into Lanthanum oxychloride with fumes of water and HCl.
- On arc melting metal with carbon in inert atmosphere, metal carbide is formed which has one electron in the conduction band with formula LnC2 and Ln4(C2)3. These carbides with water produce acetylene and hence are called acetylides.
- At high temperatures lanthanides react with n.P, As, Sb. Like AlN, these nitrides also give ammonia on getting wet with water.
- Lanthanides also form a wide variety of oxo salts with nitrates, sulphates phosphates.
- The +3 lanthanide compounds are much more reactive than Aluminium compounds but slightly more reactive than Magnesium compounds (refer to the electrode potentials). They react slowly with cold water but rapidly with hot water.
- Hydroxides are precipitated by ammonia as gelatinous precipitates. They are less basic than Ca(OH)2 but more basic than Al(OH)3.
- Above 300-400°c lanthanides react with hydrogen to form solid hydrides. These hydrides have a non stoichiometric formula with 2H-ions while the metal is in +3 state. Yb forms approximately YbH2.5 hydride.
- Lanthanides tarnish readily in air, forming oxides. On heating with oxygen also they form the oxide M2O3. Ce is an exception and forms CeO2.
- Anhydrous halides are made by heating metal and halogen or alternatively, by heating oxide with the appropriate ammonium halide.
- Hydrated lanthanum chloride on heating dissociates into Lanthanum oxychloride with fumes of water and HCl.
- On arc melting metal with carbon in inert atmosphere, metal carbide is formed which has one electron in the conduction band with formula LnC2 and Ln4(C2)3. These carbides with water produce acetylene and hence are called acetylides.
- At high temperatures lanthanides react with n.P, As, Sb. Like AlN, these nitrides also give ammonia on getting wet with water.
- Lanthanides also form a wide variety of oxo salts with nitrates, sulphates phosphates.
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