Question

It is desired to produce an aqueous solution of nitric acid (HNO3) at 5% by weight, to achieve this it has a tank with a maximum capacity of 100kg. By mistake an operator fills the tank with an 8% by weight aqueous solution of nitric acid. To solve the error at a given moment, water is added to the tank at a rate of 4 kg / min and the nitric acid solution overflows at the same speed. Consider that the tank is perfectly mixed. It is requested:

a. Obtain the nitric acid composition in the stream leaving the tank in% weight after 5 minutes that water was added.

b. How long will the system take to reach a composition in the solution within 5% by weight of nitric acid.

Answer 1

Mass of Chemical in Tank = 100kg

Mass of Nitric Acid (8%) = 8kg

Mass of water = 100-8 = 92kg

A. After 5 minutes, water entered will be = 5*4 = 20kg

Total water would be = 92+20 = 112kg

Same will be exiting the tank, therefore %wt concentration = 8/112+8 = 8/120 = 6.67%

B. The time at which the solution will reaach 5% will be the time at which solution overflowing will be also of 5%

Therefore, 0.05 = 8 / (8+92+x)

x = 60

Therefore, after 60 kg water has been added.

Rate of water addition = 4kg/min

For 60kg, time, t = 60/4 = 15

time = 15minute