Question

The stoichiometric constants for the reaction $pCu+qHN{O}_3\to rCu(N{O}_3{)}_2+sNO+t{H}_{2}O$ p, q, r ,s and t respectively are:

• A. 3, 3, 3, 2, 3
• B. 3, 2, 3, 2, 4
• C. 3, 8, 3, 2, 4
• D. 2, 3, 3, 3, 2

Answer 1

Answer: (C)

3, 8, 3, 2, 4

Given reaction:

$pCu+qHN{O}_3\to rCu(N{O}_3{)}_2+sNO+t{H}_{2}O$

Assign the oxidation states as:

$\stackrel{0}{Cu}+H\stackrel{+5}{N}{O}_3\to \stackrel{+2}{Cu}(\stackrel{+5}{N}{O}_3{)}_2+\stackrel{+2}{N}O+H_{2}O$

$\therefore$ for a total change of 6 electrons in reduction of N and oxidation of Cu multiply by 2 and 3 respectively

$3\stackrel{0}{Cu}+2H\stackrel{+5}{N}{O}_3\to 3\stackrel{+2}{Cu}(\stackrel{+5}{N}{O}_3{)}_2+2\stackrel{+2}{N}O+H_{2}O$

-Balance N

$3\stackrel{0}{Cu}+8H\stackrel{+5}{N}{O}_3\to 3\stackrel{+2}{Cu}(\stackrel{+5}{N}{O}_3{)}_2+2\stackrel{+2}{N}O$

-Balance O and H by adding $H_{2}O$

$3\stackrel{0}{Cu}+8H\stackrel{+5}{N}{O}_3\to 3\stackrel{+2}{Cu}(\stackrel{+5}{N}{O}_3{)}_2+2\stackrel{+2}{N}O+4H_{2}O$

comparing the above balanced reaction with given reaction we get:

p=3,q=8,r=3,s=2,t=4