Question

1) One method of producing drinkable water is to force seawater through a membrane that does not allow the salt to pass through. Such a process is called reverse osmosis (RO) and the membrane a reverse osmosis membrane. A large reverse osmosis facility continuously filters 2300 L of seawater per hour. The seawater contains sodium chloride (NaCl) at a concentration of 1.4 M. Two streams emerge from the RO facility: (1) a “brine” stream with a sodium chloride concentration of 5.6 M and flow rate of 560 L/hr and (2) a drinking water stream. The densities of the three streams can be considered to be the same. What is the sodium chloride concentration in the drinking water?

Answer 1

Solution :-

2300 L salt water with 1.4 M NaCl

Brine stream = 560 L at 5.6 M

Lets calculate the total NaCl moles in the sea water

Moles = molarity * volume

           = 1.4 mol per L * 2300 L

          = 3220 mol

Now lets calculate the moles of NaCl in the brine stream

Moles of NaCl = 5.6 mol per L * 560 L

                          = 3136 mol

So moles of NaCl remain in drinking water = 3220 mol – 3136 mol = 84 mol

Volume of drnking water = 2300 L – 560 L = 1740 L

Now lets calculate the molarity of the NaCl in the drinking water

Molairity of drinking water = moles / volume

                                                  = 84 mol / 1740 L

                                                  = 0.0483 M

So the NaCl molarity in the drinking water is 0.0483 M