Question

what happens when,
a. Borax is heated strongly
b. boric acid is added to water
c. aluminium is treated with dilute NaOH
d. BF3 is reacted with ammonia ?​

Answer 1

AnSwer :-

(a) When heated, borax undergoes various transition. It first loses water molecules and swells, then it turns into a transparent liquid, solidifying to a glass-like material called borax bead.

$\sf Na_2B_4O_7.10H_2O \overset{\Delta}\longrightarrow Na_2B_4O_7 \overset{\Delta}\longrightarrow 2NaBO_2 + B_2O_3$

(b) When boric acid is added to water, it accepts electrons from -OH ion.

$\sf B(OH)_3 + 2HOH \longrightarrow [B(OH)_4]^{-} + H_3O^+$

(c) Al reacts with dilute NaOH to from sodium tetradroxoaluminate (lll). Hydrogen gas is liberated in the process.

$\sf 2Al_{(g)} + 2NaOH_{(aq)} + 6H_2O_{(l)} \longrightarrow 2Na^+ [Al(OH)_4]_{(aq)} + 3H_{2(g)}$

(d) BF$_3$ (a Lewis acid) reacts with NH$_3$(a Lewis base) to form an adduct. This results in a complete octet around B in BF$_3$.

$\sf F_3B + :NH_3 \longrightarrow F_3B \longleftarrow : NH_3$