Question

Borax in water gives
$B_4O_7^{2-} + 7H_2O\to 4H_3BO_3 + 2OH$
How many grams of Borax $(Na_2B_4O_7 . 10H_2O)$ are required to prepare $50 \,ml$ of $0.2 \,M$ solution.

• A. $0.32\, g$
• B. $3.82\, g$
• C. $0.28\, g$
• D. None of these

Answer 1

Answer: (B)

The $n$-factor or valency factor of borax in the above reaction is $2$
Meq. of borax in $50\, ml$ solution $= 50 \times 0.2 \times 2 = 20$
Let weight of borax required $= W$
$\frac{W}{382} \times 2 \times 1000 = 20$
$\therefore W_{(Na_2B_4O_7. 10H_2O)} = 3.82$