Atank contains 90 kg of salt and 2000 l of water. pure water enters a tank at the rate 6 l/min. the solution is mixed and drains from the tank at the rate 3 l/min.

(a) what is the amount of salt in the tank initially? (in kg)

(b) find the amount of salt in the tank after 3.5 hours. (in kg)

(c) find the concentration of salt in the solution in the tank as time approaches infinity. (assume your tank is large enough to hold all the solution.) ( in kg/l)

a) 90 kg

b) 68.4 kg

c) 0 kg/L

Explanation:

Mass balance:

w is the mass flow

m is the mass of salt

v is the volume flow

C is the concentration

a) Initially: t=0

b) t=210 min (3.5 hr)

c) If time trends to infinity the  division trends to 0 and, therefore, m trends to 0. So, the concentration at infinit time is 0 kg/L.

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assuming that your periodic table has eighteen columns, you should highlight   the four elements in the third column from the left of the table.

neutral atoms of elements after calcium contain d electrons. the energy of d orbitals of a particular main shell lies between the energy of the s and p orbitals of the next main shell. for example, electrons in the have energy higher than those in the orbital while lower than those of the orbital.

by the aufbau principle, electrons fill orbitals one at a time, starting from those of the lowest energy. the orbital is therefore filled right after orbitals and before orbitals.  

potassium has electron configuration and calcium . the s orbital of a main shell holds a maximum of two electrons. the next element would thus have the electron configuration and satisfy the requirements.

a neutral atom of the element contains three electrons on top of the most recent noble gas element. it should thus be placed in the third column of the periodic table. both scandium and yttrium would satisfy the conditions. an aufbau diagram indicates that the 4f orbital is filled before the 5d. however, it appears that exceptions exists for both lanthanum and actinium. neutral atoms of the two d-block elements also demonstrate the and should be highlighted as well.