First slide

Orthoboric acid

Question

Hot and concentrated solution of borax is treated with hydrochloric acid to give A and B. “B” on strong heating undergoes dehydration to give C. then “C” is

Easy

A

An acidic oxide
B

A basic oxide
C

An amphoteric oxide
D

Salt of a strong acid and strong base

Solution

$\mathop {N{a_2}{B_4}{O_7}}\limits_{Borax} + 2HCl + 5{H_2}O \to \mathop {2NaCl}\limits_A + \mathop {4{H_3}B{O_3}}\limits_B$
OR $\mathop {2{H_3}B{O_3}}\limits_B \xrightarrow{{Strong\,\,heating/\operatorname{Re} d\,hot}}\mathop {\mathop {{B_2}{O_3}}\limits_{Boric\,anhydride} }\limits_C + 3{H_2}O$
$\mathop {{H_3}B{O_3}}\limits_{Ortho\,boricacid} \xrightarrow[{ - {H_2}O}]{{{{100}^0}c}}\mathop {HB{O_2}}\limits_{meta\,boricacid}$
$\mathop {4HB{O_2}}\limits_{meta\,boricacid} \xrightarrow[{ - {H_2}O}]{{{{160}^0}c}}\mathop {{H_2}{B_4}{O_7}}\limits_{Tetra\,boric\,acid}$
${H_2}{B_4}{O_7}\xrightarrow[{ - {H_2}O}]{{\operatorname{Re} d\,hot}}\mathop {\mathop {2{B_2}{O_3}}\limits_{Boric\,\,\,anhydride} }\limits_{Acidic\,\,\,\,oxide}$

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