pBlock ElementsII - Result Question 131
####16. The reaction of white phosphorus with aqueous $NaOH$ gives phosphine alongwith another phosphorus containing compound. The reaction type, the oxidation states of phosphorus in phosphine and the other product respectively are
(2012)
(a) redox reaction, -3 and -5
(b) redox reaction, 3 and +5
(c) disproportionation reaction, -3 and +5
(d) disproportionation reaction, -3 and +3
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Solution:
- The reaction of white phosphorus with aqueous alkali is
$$ P _4+3 NaOH+3 H _2 O \longrightarrow PH _3+NaH _2 PO _2 $$
In the above reaction, phosphorus is simultaneously oxidised $\left[P _4(0) \longrightarrow NaH _2 \stackrel{+1}{P} O _2\right]$ as well as reduced $\left[P _4(0) \longrightarrow \stackrel{-3}{P} H _3\right]$ Therefore, this is an example of disproportionation reaction. Oxidation number of phosphorus in $PH _3$ is -3 and in $NaH _2 PO _2$ is +1 . However, +1 oxidation number is not given in any option, one might think that $NaH _2 PO _2$ has gone to further decomposition on heating.
$$ 2 NaH _2 PO _2 \stackrel{\Delta}{\longrightarrow} Na _2 H \stackrel{+5}{P} O _4+PH _3 $$
