First slide

Orthoboric acid

Question

Statement I : BCl₃ and AlCl₃ are both Lewis acids and BCl₃ is stronger than AlCl₃
Statement II : H₃BO₃ is strong tribasic acid

Moderate

A

Both the statements are true
B

Both the statements are false
C

I is false and II is true
D

I is true and II is false

Solution

III_A group trihalides are lewis acids as they accepts the electron pair from electron pair donors
$_5B{^*}\,\,\,\,1{s^2}2{s^1}2{p_x}^12{p_y}^12{p_z}^0$
The electron pair accepting tendency of trihalides is due to the presence of empty p-orbital in its valency shell.
I) As the size of central atom increases,
metallicnature increases,
electronegativity decreases,
and hence electron pair accepting tendency decreases,
$\therefore$ Lewis acidic streangth decreases.
Hence acidic strength order of III_A group trihalides: Bcl₃ > AlCl₃ > GaCl₃ > InCl₃ > TlCl₃
II) ${H_3}B{O_3} + {H_2}0\,\,\, \to \,\,{[B{(OH)_4}]^ - } + \,{H^ + }$
                              $OR$
H₃BO₃    is not a protic acid and hence it is not a tribasic acid ,H₃BO₃ is a Lewis acid and the released proton is not from H₃BO₃ and the H⁺ion is released from water.
    Therefore statement-I is true and II is false.

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