150,000 mol of aqueous phosphoric acid (H3PO4) solution contains 5.00% H3PO4 by moles. The solution is concentrated by adding pure H3PO4 at a rate of 20.0 L/min.
1) Write a differential mole balance on H3PO4 and write the initial condition. (Hint: Start by defining np to be the total quantity of H3PO4 in the tank at any given time.
2) Solve to find np(t). Then derive an expression for the mole fraction of H3PO4 in the solution, xp(t).
3) How long will it take to concentrate the solution to 15% H3PO4?