Question

Thionyl chloride on reaction with white phosphorus gives a compound of phosphorus 'C' which on hydrolysis gives an oxo acid 'O'. The correct statements about C and O are
I. Shape of 'C' is pyramidal
II. 'O' is a dibasic acid
III. 'O' is a monobasic acid
IV. 'C' on reaction with acetic acid gives 'O'

• A. I \& II only
• B. II \& IV only
• C. I, III \& IV only
• D. I, II \& IV only

Hint:

The basicity of phosphorus oxoacids is a common point of confusion. It's determined by the number of P-OH bonds, not the total number of H atoms. Draw the structures to be sure: - H₃PO₂ (Hypophosphorous): 1 P-OH bond \(\rightarrow\) monobasic. - H₃PO₃ (Phosphorous): 2 P-OH bonds \(\rightarrow\) dibasic. - H₃PO₄ (Phosphoric): 3 P-OH bonds \(\rightarrow\) tribasic.

Answer 1

The Correct Option is D

Step 1: Identify C: Reaction of White Phosphorus with Thionyl Chloride (\( \text{SOCl}_2 \)): \[ \text{P}_4 + 8\text{SOCl}_2 \to 4\text{PCl}_3 + 4\text{SO}_2 + 2\text{S}_2\text{Cl}_2 \] Compound C is \( \text{PCl}_3 \) (Phosphorus Trichloride).
Step 2: Identify O: Hydrolysis of \( \text{PCl}_3 \): \[ \text{PCl}_3 + 3\text{H}_2\text{O} \to \text{H}_3\text{PO}_3 + 3\text{HCl} \] Acid O is \( \text{H}_3\text{PO}_3 \) (Orthophosphorous acid).
Step 3: Analyze Statements: - Statement I: Structure of \( \text{PCl}_3 \) involves \( sp^3 \) hybridization with 1 lone pair. Geometry is Tetrahedral, Shape is Pyramidal. (True) - Statement II: Structure of \( \text{H}_3\text{PO}_3 \) has two P-OH groups and one P-H group. It has 2 ionizable hydrogens. Hence, it is Dibasic. (True) - Statement III: It is monobasic. (False) - Statement IV: \( 3\text{CH}_3\text{COOH} + \text{PCl}_3 \to 3\text{CH}_3\text{COCl} + \text{H}_3\text{PO}_3 \). It yields O. (True) Conclusion: Statements I, II, and IV are correct.