Question

$A$ and $B$ are formed when borax is dissolved in water. $C$ and $B$ are formed when borax is reacted with aqueous $HCl$ solution. What are $A$ and $C$ respectively?

• A. $NaCl , NaOH$
• B. $NaOH , NaCl$
• C. $NaBO _{2}, NaCl$
• D. $NaOH , NaBO _{2}$

Answer 1

Answer: (B)

The reaction of borax $\left( Na _{2} B _{4} O _{7}\right)$ with water occurs as follows:

$Na _{2} B _{4} O _{7}+7 H _{2} O \longrightarrow \underset{(B)}{4 H _{3} BO _{3}}+\underset{(A)}{2 NaOH}$

While, borax reacts with $HCl $ (dil.) as follows:

$Na _{2} B _{4} O _{7}+2 HCl ($ dil. $) \longrightarrow 2 NaCl +4\left[ B \left( H _{2} O \right)( OH )_{3}\right]$

Or
$Na _{2} B _{4} O _{7}+2 HCl +9 H _{2} O \longrightarrow \underset{C)}{2 NaCl} +4\left[ B \left( H _{2} O \right)( OH )_{3}\right]$

or, $Na _{2} B _{4} O _{7}+2 HCl \cdot l 0 H _{2} O \longrightarrow \underset{(B)}{4 H _{3} BO _{3}}+\underset{(C)}{2 NaCl} +5 H _{2} O$

Hence, $(A)= NaOH$ and $(C)= NaCl$