Phosphorus halides - class-XII

A translucent white waxy solid (A) reacts with excess of chlorine to give a yellowish white powder (B). Here B is $PCl _5$.$PCl _5$ reacts with organic compounds containing -OH group converting them into chloro derivative $POCl _3. $.$PCl _5$ on hydrolysis gives (C).C is $POCl _3$ and is finally $POCl _3$ converted to phosphoric acid.

So  (A), (B) and (C) are $P _{4}$,$PCl _{5}$,$POCl _{3}$.

Hence option C is correct.

White P is reactive due to strain.
$P _{4}+6Cl _{2}\ \to \ 4PCl _{3}$
(White P)

All have dimer forms

$NO$ as $N _{2}O _{2}$

$NO _{2}$ as $N _{2}O _{4}$

$P _{2}O _{3}$ as $P _{4}O _{6}$

The oxidation state of ${P}$ in ${P}{Cl} _{3}$ is ${+3}$.
Each Chlorine atom has an oxidation number of ${-1}$. There are three chlorine atoms, hence the total oxidation number of the Chloride ions in ${-3}$. ${PCl} _{3}$ molecule is neutral. Hence the oxidation number of Phosphorus should be ${+3}$

The boiling point of ${PCl} _{3}$ is ${76.1}^{o}$ ${C}$

The hybridization of ${PCl} _{3}$ is ${sp}^{3}$. Phosphorus has five electrons in its outermost shell. Thus it forms three sigma bonds with three neighbouring Chlorine atoms. The remaining two electrons remain as a lone pair on Phosphorus atom. Thus these three sigma bonds and one lone pair, make this molecule ${sp}^{3}$ hybridized.

$PCl _3$ is a polar covalent molecule. It is polar because chlorine atoms are more electronegative than phosphorus atom and hence the polartity of the molecule is towards Chlorine atoms.
It is covalent because, Phosphorus has ive electrons in its outermost shell. It requires three more to complete its octet. Each chlorine atom has seven electrons in their outermost shell, they all require one electron each to complete their octet. Thus both phosphorus and chlorine complete their octet by mutually sharing their electrons. Hence this molecule is polar covalent in nature.

During the indusrial preparation of ${PCl} _{3}$, ${PCl} _{5}$ or Phosphorus Pentachloride is produced as an impurity. The balanced equation can be written as-
${PCl} _{3}$ ${+}$ ${Cl} _{2}$ ${=}$ ${PCl} _{5}$
Thus this impurity formation can be stopped by continual removal of ${PCl} _{3}$ as it is formed.

$PCl _3$ on hydrolysis gives $HCl$ and $H _3PO _3$.

$PBr _{3}+3H _{2}O\ \to \ H _{3}PO _{4}+HBr$
HBr is covalent $H _{3}PO _{4}$ is ionic. Solution conducts electricity due to ions.
So aqueous solution of $PBr _{3}$ conducts electricity due to presence of $H _{3}PO _{4}$.

The correct chemical equation is :

Solution:-
$PCl _3+3H _2O\rightarrow H _3\ PO _3+3HCl$

 Hydrolysis of $PCl _3$ gives:

Due to low ignition temperature of white phosphorus, it undergoes oxidation in presence of air which slowly raises its temperature and after a few moments it catches fire spontaneously. Due to this reason, it is stored under water. Ignition temperature ofred phosphorus is high Black phosphorus is crystalline in nature. Phosphorus forms a number of hydrides

${P}{Cl} _{3}$ is a colorless liquid or has a slight yellow color (but not bright yellow).

Phosphorus trichloride is prepared from phosphorus and chlorine. It has a pungent and irritating odour that is similar to that of hydrochloric acid.

The density of phosphorus trichloride is ${1.57}$ ${gm}{/}{cm}^{3}$

In ${ PCl } _{ 3 }$, $P$ is ${ sp }^{ 3 }$ hybridized with a lone pair. This makes its structure trigonal pyramidal. So, the correct answer is option $A$.

${PCl} _{3}$ is liquid under normal conditions. ${PCl} _{3}$ is a covalent compound. Phosphorus and each of the chlorine atoms fulfil their octet by mutually sharing their valence electrons. In general, covalent compounds have weak bond energy and hence they form liquid.

Dehydrated phosphorus trichloride in water gives phosphoric acid.

$PCl _3 + 3H _2O\rightarrow  H _3PO _3 + 3 HCl$

Hence option A is correct.

$P+Cl _2\longrightarrow \underset {(B)}{PCl _3} +\underset {(A)}{PCl _5}$

In solid state $PCl _5$ tries  to exist as oppositely charged ions like

(1) $PCl _4^{+}$ and (2) $PCl _6^{-}$ as the ionic bonding enhances the crystalline nature .

also $PCl _4^{+}$  is tetrahedral , while $PCl _6^{-}$ is octahedral . these structure fit well into each other which gives more stability to solid structure .

Hence option D is correct.

$PCl$ on reaction with these $4$ compounds produces $POCl _3$:

$PCl _{5}$ readily dissociates into $PCl _{3}$ and chlorine gas and therefore acts as a good chlorinating agent.

SI is too big for small P.
SI atoms cannot fil around small P. So $PI _{s}$ does not exist.

Phosphorus pentoxide (P4O10) reacts with hot water to produce phosphoric acid (H3PO4).

(A) Calcium cyanamide on treatment with steam under pressure gives ${NH _3}$ and ${Ca CO _3}$
 $\displaystyle CaCN _2+3H _2O \text { (steam)} \xrightarrow {\displaystyle \text {3 atm}} CaCO _3+ 2NH _3$
(B) ${PCl _5}$ is kept in well stopped bottle because it reacts readily with moisture
 $\displaystyle PCl _5+H _2O \rightarrow POCl _3+2HCl$
 $\displaystyle PCl _5+4H _2O \rightarrow H _3PO _4+5HCl$
(C) Ammonium nitrite on heating gives nitrogen and water.
 $\displaystyle NH _4NO _2 \rightarrow N _2  +2H _2O$
(D)Cane sugar reacts with conc. ${H NO _3}$ to form oxalic acid
 $\displaystyle C _{12}H _{22}O _{11}+36HNO _3 \rightarrow 6(COOH) _2+36NO _2+23H _2O$

PCl$ _5$ (solid) dissociates into PCl$ _4^+$ and PCl$ _6^-$. LiH reacts with AlH$ _3$ forming LiAlH$ _4$. These are facts. $NH _3$ is not protonated. On protonation, it forms $NH _4^+$ion. $H _3PO _2$ on heating does not form $PH _3$ and $H _3PO _3$.

In the reaction of ethanol (CH3CH2OH) with PCl5, the hydroxyl group (-OH) is replaced by a chlorine atom. This involves the breaking of the O-H bond (Z position) and the C-O bond.

In solid state, $PCl _5$  prefers to exist as oppositely charged ions like $[PCl _4]^+$ & $[PCl _6]^-$ as the ionic bonding enhances the crystalline nature.

In solid state, $PCl _5$ prefers to exist as oppositely charged ions like $[PCl _4]^+$ & $[PCl _6]^-$ as the ionic bonding enhances the crystalline nature. Also, $[PCl _4]^+$ is tetrahedral while $[PCl _6]^-$ is octahedral, these structures fit well into each other providing extra stability to the soild structure.

In solid state, $PCl _5$ prefers to exist as oppositely charged ions like $[PCl _4]^+ [PCl _6]^-$ as ionic bonding enhances the crystalline nature. Also, $[PCl _4]^+$ is tetrahedral while $[PCl _6^-]$ is octahedral. These structures fit well into each other providing extra stability to the solid structure.

In solid state, $PCl _5$ prefers to exist as oppositely charged ions like $[PCl _4]^+ PCl _6^-$ as ionic bonding enhances the crystalline nature. Also, $[PCl _4]^+  = sp^3$ is tetrahedral while $[PCl _6^-]$ is octahedral. These structures fit well into each other providing extra stability to the soild structure.

In limited amount of water,
$PCl _5 (s)+H _2O (l)\rightarrow POCl _3(l) + 2HCl(aq)$
In large amount of water,
$PCl _5(s) +4H _2O(l)\rightarrow H _3PO _4+ 5HCl$

Solid $PCl _5$ exists as tetrahedral $PCl^{+} _{4}$ and octahedral  $PCl^{-} _{6}$ ions.
$2PCl _5 \rightleftharpoons [PCl _4]^+ (tetrahedral) + [PCl _6]^-(octahedral)$
Solid $PBr _5$ exists as $PBr^{+} _{4}Br^{-}$.
$PBr _5 \rightleftharpoons [PBr _4]^+(tetrahedral) Br^-$
Solid $N _2O _5$ exists as $NO^{-} _3$ and $NO^{+} _{2}$.
$N _2O _5 \rightleftharpoons NO^{-} _3 + NO^{+} _{2}$
Oxides of phosphorus $P _2O _3$ and $P _2O _5$ exist as dimers $P _4O _6$ and $P _4O _{10}$. 

In solid state, position of ions are fixed, and hence, cannot conduct electricity.

$(i) P{Cl} _{5}+{SO} _{2}\rightarrow SO{Cl} _{2} (A)+PO{cl} _{3} (B)$

$PCl _{5}+SO _{2}\rightarrow POCl _{3}+SOCl _{2}$

The cation $PCl^+ _4$ and the anion $PCl _6^-$ are tetrahedral and octahedral which are more stable then $PCl _5$ due to symmetry.

The given statement is True.
 
$\displaystyle PCl _5$ molecule has trigonal bipyramidal geometry which is unstable as axial P-Cl bonds are slightly larger than equatorial P-Cl bonds. Also some bond angles are of 90 deg and others are of 120 deg. Due to this, trigonal bipyramidal geometry is not regular and not stable. Hence, in solid state, $\displaystyle PCl _5$ molecule dissociates into tetrahedral $\displaystyle [PCl _4]^+$ and octahedral $\displaystyle [PCl _6]^-$
$\displaystyle 2PCl _5 \rightleftharpoons [PCl _4]^+ +[PCl _6]^- $

In gaseous and molten state $PCl _5$ is neutral molecule with trigonal bipyramidal symmetry.

In solid state $PCl _5$ is ionic which forms $PCl _4^{+}$, $PCl _6^{-}$. The cation and anion $PCl _4^{+}$, $PCl _6^{-}$ are tetrahedral and octahedral respectively.