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Question
The amphoteric hydroxide is
The amphoteric hydroxide is
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Solution
The correct option is A Be(OH)2
For group-2 metal hydroxides, basicity increases down the group, as:
Be(OH)2<Mg(OH)2<Ca(OH)2<Sr(OH)2<Ba(OH)2
This is because as the size of metal atom increases, M−OH bond length increases or M−OH bond become weaker thus readily breaks to release OH− ions which are responsible for the basicity of these solutions.
But Be(OH)2 shows amphoteric (basic as well as acidic) character as it reacts with acid and alkali both which is shown in the following reactions. Be(OH)2 as a base:
Be(OH)2+2HCl→BeCl2+2H2O
Be(OH)2 as an acid:
Be(OH)2+2NaOH→Na2[Be(OH)4]
Theory
Oxides and hydroxides:
1. Burn in oxygen to form monoxide MO, have rock-salt structure except for BeO.
2. BeO is covalent in nature, while the oxides of other elements are ionic in nature.
3. The enthalpies of formation of these oxides are quite high, hence very stable to heat.
All these oxide are basic in nature except BeO.
They react with water to form sparingly soluble hydroxides.
MO+H2O⟶M(OH)3
Order of solubilities, thermal stabilities and basic character:
Mg(OH)2<Ca(OH)2<Sr(OH)2<Ba(OH)2
The alkaline earth metal hydroxides are less basic and less stable
than alkali metal hydroxides.
Beryllium hydroxide is amphoteric in nature as it reacts with both acids and alkalis.
Be(OH)2+2OH−⟶[Be(OH)4]2−
Be(OH)2+2HCl+2H2O⟶[Be(OH2)4]Cl2
Halides:
1. Halides of alkaline earth metals are ionic in nature except BeX2(whereX=F,Cl,Br,I
2.Beryllium halides are covalent and soluble in organic solvents.
3. BeCl2 forms dimer in the vapor phase which dissociates into monomer at temperatures above 1200 K.
4. The fluorides are relatively less soluble than the chlorides due to their high lattice energies.
Beryllium chloride has a chain structure in the solid state
The tendency to form halide hydrates gradually decreases down the group
Mg > Ca >Sr> Ba
The dehydration of hydrated chlorides, bromides and iodides of Ca, Sr and Ba can be achieved on heating.
The hydrated halides of Be and Mg on heating suffer hydrolysis.
For group-2 metal hydroxides, basicity increases down the group, as:
Be(OH)2<Mg(OH)2<Ca(OH)2<Sr(OH)2<Ba(OH)2
This is because as the size of metal atom increases, M−OH bond length increases or M−OH bond become weaker thus readily breaks to release OH− ions which are responsible for the basicity of these solutions.
But Be(OH)2 shows amphoteric (basic as well as acidic) character as it reacts with acid and alkali both which is shown in the following reactions. Be(OH)2 as a base:
Be(OH)2+2HCl→BeCl2+2H2O
Be(OH)2 as an acid:
Be(OH)2+2NaOH→Na2[Be(OH)4]
Theory
Oxides and hydroxides:
1. Burn in oxygen to form monoxide MO, have rock-salt structure except for BeO.
2. BeO is covalent in nature, while the oxides of other elements are ionic in nature.
3. The enthalpies of formation of these oxides are quite high, hence very stable to heat.
All these oxide are basic in nature except BeO.
They react with water to form sparingly soluble hydroxides.
MO+H2O⟶M(OH)3
Order of solubilities, thermal stabilities and basic character:
Mg(OH)2<Ca(OH)2<Sr(OH)2<Ba(OH)2
The alkaline earth metal hydroxides are less basic and less stable
than alkali metal hydroxides.
Beryllium hydroxide is amphoteric in nature as it reacts with both acids and alkalis.
Be(OH)2+2OH−⟶[Be(OH)4]2−
Be(OH)2+2HCl+2H2O⟶[Be(OH2)4]Cl2
Halides:
1. Halides of alkaline earth metals are ionic in nature except BeX2(whereX=F,Cl,Br,I
2.Beryllium halides are covalent and soluble in organic solvents.
3. BeCl2 forms dimer in the vapor phase which dissociates into monomer at temperatures above 1200 K.
4. The fluorides are relatively less soluble than the chlorides due to their high lattice energies.
Beryllium chloride has a chain structure in the solid state
The tendency to form halide hydrates gradually decreases down the group
Mg > Ca >Sr> Ba
The dehydration of hydrated chlorides, bromides and iodides of Ca, Sr and Ba can be achieved on heating.
The hydrated halides of Be and Mg on heating suffer hydrolysis.
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