Question

Assuming that seawater has a total ion concentration (a.k.a colligative molarity) of 1.10 Mc, calculate how many liters of seawater are needed to produce 81.0 L of fresh water at 20 °C with an applied pressure of 70.0 bar.

Answer 1

Calculate the concentration with the given information

C = , where p is pressure, R is the gas constant, T is temperature

P = 50 bar

T = 20 Celsius

T kelvin = 20 + 273.15 = 293.15 K

1 bar = 0.9869 atm

50 bar = 49.34 atm

C = 49.34 / (0.082 * 293.15) = 2.0525 M

So we have

C final = 2.0525 M

C initial = 1.1 M

For 1 liter of seawater

1.1 / (1 - W ) = 2.0525

1.1 / 2.0525 = 1 - W = 0.536

W = 1 - 0.536 = 0.464 Liters

For 81 Liters

81 / 0.464 = 174.57 Liters

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