The equilibrium: p-xyloquinone + methylene white ⇌ p-xylohydroquinone + methylene blue, may be studi — Chemical Equilibrium Chemistry Question
Question
The equilibrium: p-xyloquinone + methylene white ⇌ p-xylohydroquinone + methylene blue, may be studied conveniently by observing the difference in colour between methylene blue and methylene white. One millimole of methylene blue was added to 1.00 l of solution that was 0.24 M in p-xylohydroquinone and 0.012 M in p-xyloquinone. It was then found that 4.0% of the added methylene blue was reduced to methylene white. What is the equilibrium constant for the above reaction? The equation is balanced with 1 molecule of each of the four substances.
💡 Solution & Explanation
Let [p-X] = p-xyloquinone, [MW] = methylene white, [p-XH₂] = p-xylohydroquinone, [MB] = methylene blue. Reaction: [p-X] + [MW] ⇌ [p-XH₂] + [MB]. Initial concentrations: [p-XH₂] = 0.24 M, [p-X] = 0.012 M, [MB] = 0.001 M, [MW] = 0. 4.0% of MB is reduced, meaning 0.04 × 0.001 = 4 × 10⁻⁵ M of MB reacts with p-XH₂ to form MW and p-X. Equilibrium concentrations: [MB] = 0.001 - 0.00004 = 0.00096 M. [MW] = 0.00004 M. [p-XH₂] = 0.24 - 0.00004 ≈ 0.24 M. [p-X] = 0.012 + 0.00004 ≈ 0.012 M. K_c = ([p-XH₂][MB]) / ([p-X][MW]) = (0.24 × 0.00096) / (0.012 × 0.00004) = 20 × 24 = 480. Therefore, correct answer is 0480.