In a certain first-order reaction, B^n+ is getting converted to B^(n+4)+ in solution. The rate constant of this reaction is measured by titrating a volume of the solution with a reducing agent which r

Question

In a certain first-order reaction, B^n+ is getting converted to B^(n+4)+ in solution. The rate constant of this reaction is measured by titrating a volume of the solution with a reducing agent which reacts only with B^n+ and B^(n+4)+. In the process, it converts B^n+ to B^(n-2)+ and B^(n+4)+ to B^(n-1)+. At t = 0, the volume of reagent consumed is 25 ml and at t = 10 min, the volume used is 32.5 ml. The rate constant for the conversion of B^n+ of B^(n+4)+ is (ln 2 = 0.7, ln 5 = 1.6)

Prashant Kotian · Accepted Answer

Correct answer: C. Reducing B^n+ to B^(n-2)+ uses 2 eq. B^(n+4)+ to B^(n-1)+ uses 5 eq. At t=0, V0 ∝ 2a = 25 => a = 12.5. At t=10, Vt ∝ 2(a-x) + 5x = 2a + 3x = 32.5 => 25 + 3x = 32.5 => x = 2.5. Then a-x = 10. k = (1/10) ln(12.5 / 10) = 0.1 ln(1.25) = 0.1 * 0.2 = 0.02 min^-1. Therefore, correct answer is C.

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