Question

The equilibrium $p-Xyloquinone+methylenewhite\rightleftharpoons o-Xyolhydroquinone+methyleneblue$ may be studied conveniently by observing the difference in color of methylene white and methylene blue. It was then found that 4 percent of the added methylene blue was reduced to methylene white. What is the equilibrium constant of the above reaction? The equation is balanced with one mole each of 4 substances.

• A. $K_c=496$
• B. $K_c=500$
• C. $K_c=540$
• D. $K_c=576$

Answer 1

The correct option is D $K_c=576$

Let the reaction be represented as $A+B\to C+D$
A is pxyloquinone, B is methylenewhite, C is Xyolhydroquinone and D is methyleneblue
4 mol% of D is reduced to B.
The equilibrium number of moles of A, B, C and D will be 4,4, 96 and 96 respectively.
The expression for the equilibrium constant bencomes $K_c=\frac{\left[C\right]\left[D\right]}{\left[A\right]\left[B\right]}=\frac{96\times 96}{4\times 4}=576.$