5) (20 points) A water tower containing 4,000 m³ of water has been taken out of service for installation of a chlorine monitor. The concentration of chlorine in the water tower was 2.0 mg/L when the tower was taken out of service. If the chlorine decays with a rate constant of 1.0 d'', what is the chlorine concentration when the tank is put back in service 8 hours later? What mass of chlorine (in kg) much be added to the tank to raise the level back to 2.0 mg/L? For this problem assume the tank is well-mixed.

Fig: 1