A student studies the bleaching of crystal violet (CV+) by NaOH using a spectrophotometer at 590 nm. With NaOH in large excess (pseudo-first-order), the absorbance is recorded versus time: t (s): 0 30 60 90 120 150 A: 0.800 0.610 0.464 0.353 0.269 0.205 A plot of ln(A) versus t is linear with slope = -0.00908 s^-1.
Repeating the experiment with twice the [NaOH] gives k_obs = 0.0182 s^-1. What is the order with respect to OH-?
- A
Second order
- Bcheck_circle
First order
- C
One-half order
- D
Zero order
Explanation
Doubling [OH-] doubled k_obs, indicating k_obs proportional to [OH-]^1, so first order in OH-.