JEE Main 2017 · Chemistry · s-Block, p-Block Elements and Hydrogen · medium

White phosphorus (P4, M=124) is heated with excess concentrated NaOH solution, giving phosphine and sodium hypophosphite. From 6.2 g of P4, the…

Single correct option

White phosphorus (

\mathrm{P_4}

M=124

) is heated with excess concentrated NaOH solution, giving phosphine and sodium hypophosphite. From

6.2\ \mathrm{g}

\mathrm{P_4}

, the volume of

\mathrm{PH_3}

at STP (

22.4\ \mathrm{L\,mol^{-1}}

) and the mass of

\mathrm{NaH_2PO_2}

(

M=88

) formed are, respectively

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Answer: (B) $1.12\ \mathrm{L}$ and $13.2\ \mathrm{g}$

Balanced reaction (disproportionation of P(0)):

\mathrm{P_4+3NaOH+3H_2O\to PH_3+3NaH_2PO_2}

. Moles of

\mathrm{P_4}=6.2/124=0.050

\mathrm{PH_3}=0.050

mol

=0.050\times22.4=1.12

\mathrm{NaH_2PO_2}=3\times0.050=0.150

mol

=0.150\times88=13.2

g. A common mistake is to use 3 mol of

\mathrm{PH_3}

per

\mathrm{P_4}

or only 1 mol of hypophosphite.

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