Question

Prior to the spill, the mining waste holding pond was intended to temporarily hold water to allow time for particles to settle and the pH to be adjusted. Suppose the pond was used as intended, assuming no flow in or out. Cyanide (a common chemical used to extract gold from ore) is present in the pond at a concentration of 0.5 mg/L. Cyanide has a decay rate of 0.05/hr. What would the cyanide concentration be after 1 day of holding the water in the pond

Answer 1

0.15 mg/L

Step-by-step explanation:

Decay is a first order process so;

ln[A] = ln[A]o - kt

[A]o = initial concentration = 0.5 mg/L

[A] = concentration at time t

t = time taken = 1 day = 24 hours

k = decay constant = 0.05/hr

ln[A] = ln(0.5) - 0.05(24)

ln[A] = -0.693 - 1.2

ln[A] = -1.893

e^ln[A] = e^-1.893

[A] = 0.15 mg/L