Question

What are $X, Y, Z$ in the following reactions?

	X	Y	Z
(a)	$H_2SO_4, 443\,K$	$85 \% \,H_3PO_4, \,440\,K$	$20\% \,H_3PO_4, \, 358\,K$
(b)	$85 \% H _{3} PO _{4}, \,440\, K$	$H_2SO_4, \,443\,K$	$20\% \,H_3PO_4, \, 358\,K$
(c)	$20\%\, H_3PO_4,\, 358\,K$	$H_2SO_4, \,443\,K$	$85\%\,H_3PO_4, \,440\,K$
(d)	$H_2SO_4, \,443\,K$	$20\%, H_3PO_4, \,358\,K$	$85\%\,H_3PO_4, \,440\,K$

• A. a
• B. b
• C. c
• D. d

Answer 1

Answer: (B)

$CH_3CH_2OH \ce{ ->[{H_2SO_4 (Y)}][{443 K}] }CH_2=CH_2+H_2O$



These reactions are known as dehydration reactions where $H _{3} PO _{4}$ and $H _{2} SO _{4}$ are dehydrating agents. Ethanol undergo dehydration by heating with conc. $H _{2} SO _{4}$ at $443\, K$ whereas $2^{\circ}$ alcohols by $85 \% H _{3} PO _{4}$ at $440 K$ and $3^{\circ}$ alcohols by $20 \% H _{3} PO _{4}$ at $358 \,K$.