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JEE Advanced

Exam: JEE Advanced
Subject: Chemistry
Chapter: p Block Elements (Group 13 & 14)

JEE Advanced · Chemistry · p Block Elements (Group 13 & 14)

How many grams of borax (Na_2 ~B_4 O_7 .10 H_2 O) are required to...

How many grams of borax

\left(\mathrm{Na}_2 \mathrm{~B}_4 \mathrm{O}_7 .10 \mathrm{H}_2 \mathrm{O}\right)

are required to prepare 100 mL of 0.5 M OH⁻ solution? \{Atomic Mass;

B=10.8 \mathrm{amu}, O=16 \mathrm{amu}, \mathrm{Na}=23 \mathrm{amu}\}\mathrm{B}_4 \mathrm{O}_7^{-2} \longrightarrow 4 \mathrm{H}_3 \mathrm{BO}_3+2 \mathrm{OH}^{-}

Options

A4.76 g
B9.53 g
C19.06 g
D1.59 g

Correct answer

B. 9.53 g

Step-by-step solution

Mole of

\mathrm{OH}^{-}

present in 100 mL 0.5 M solution = 0.05 mole 1 mole of borax gives 2 moles of

\mathrm{OH}^{-}

0.025 mole of borax gives

\mathbf{0 . 0 5}

mole of

\mathrm{OH}^{-}

Weight of borax needed is

0.025 \times 381.27=9.53 \mathrm{~g}

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