Question

What volume of hydrogen gas, at $273K$ and $1atm$ pressure will be consumed in obtaining $21.6g$ of elemental boron (atomic mass $=$ $10.8$) from the reduction of boron trichloride by hydrogen?

• A. $89.6L$
• B. $67.2L$
• C. $44.8L$
• D. $22.4L$

Answer 1

The correct option is B $67.2L$

The reaction would be $2BC{l}_3+3H_2\to 2B+6HCl$

In the reaction to obtain $2moles$ of elemental boron at S.T.P requires $3moles$ of $H_2$ gas.

The moles of boron in $21.6g=\frac{21.6}{10.8}=2moles$

These $2moles$ of $B$ need $3moles$ of $H_2$ at STP.

The volume of $1mole$ of gas at $STP=22.4L$

Therefore, the volume of $3moles=22.4\times 3=67.2L$