Question

The reaction of white phosphorus with aqueous $NaOH$ gives phosphine along with another phosphorus containing compound. The reaction type, the oxidation states of phosphorus in phosphine and the other product respectively are

• A. redox reaction, $- 3$ and $- 5$
• B. redox reaction, $+ 3$ and $+ 5$
• C. disproportionation reaction, $- 3$ and $+ 5$
• D. disproportionation reaction, $- 3$ and $+ 3$

Answer 1

Answer: (C)

disproportionation reaction, $- 3$ and $+ 5$

Answer 2

The reaction of white phosphorus with aqueous alkali is $P_4 + 3NaOH + 3H_2O \longrightarrow PH_3 + NaH_2P O_2$ In the above reaction, phosphorus is simultaneously $oxidised [P_4 ( 0 )\longrightarrow NaH_2\, ^{+1}_{P} O_2]$ as well as reduced $[P_4(0) \longrightarrow\, ^{-3}_{P} H_3]$. Therefore, this is an example of disproportionation reaction. Oxidation number of phosphorus in $PH_3\, is\, - 3\, and\, in\, NaH_2P O_2$ is + L
However, + 1 oxidation number is not given in any option, one might think that $NaH_2P O_2$ has gone to further decomposition on heating. $2NaH_2P O_2\, \, \xrightarrow{\Delta}\, \, \, Na_2H\, ^{+5}_{P} O_4 +PH_3$