First slide

Borax

Question

Statement 1: The borax ${Na}_{2} [B_{4} O_{5} {(OH)}_{4}] . 8 H_{2} O$ is a useful as primary standard for titrating against acids.
Statement 2: Aqueous solution of borax contains equal amounts of weak acid and its salt.

Difficult

A

Both statements 1 and 2 are correct
B

Statement 1 is correct and statement 2 is incorrect
C

Statement 1 is incorrect and statement 2 is correct
D

Both statements 1 and 2 are incorrect

Solution

$\begin{array}{l} {Na}_{2} [B_{4} O_{5} {(OH)}_{4}] . 8 H_{2} O + 2 HCl \\ \to 2 NaCl + 4 H_{3} {BO}_{3} + 5 H_{2} O \end{array}$
Indicator methyl orange pH range $3.1 - 4.4$
In water, borax gives both $B {(OH)}_{3} and {[B {(OH)}_{4}]}^{-} and only the {[B {(OH)}_{4}]}^{-}$ reacts with HI
Reason : ${[B_{4} O_{5} {(OH)}_{4}]}^{2 -} + 5 H_{2} O \overset{}{⇌} \underset{weak acid}{3 B {(OH)}_{3}} + \underset{its salt}{2 {[B {(OH)}_{4}]}^{-}}$
thus acts as a buffer.

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