Question

Ocean water typically contains 35 moles of salt ions dissolved in each 1000 moles of water. Assuming that ocean water has the same density as pure water convert this ratio into a molarity and calculate the expected osmotic pressure of ocean water.

Answer 1

we know that

mass = moles x molar mass

so

mass of water = 1000 x 18 = 18000

now

volume = mass / density

so

volume of water = 18000/ 1

volume of water = 18000 ml

so

volume of water = 18 L

now

molarity = moles of salt ions / volume

so

molarity = 35 / 18

molarity = 1.9444

so

the molarity is 1.944 M

now

we know that

osmotic pressure = i x C x R x T

considering ocean water contains only NaCl

NaCl ---> Na+ + Cl-

there are 2 particles after dissociation

so

i = vanthoff factor = 2

so

osmotic pressure = 2 x 1.944 x 0.0821 x 298

osmotic pressure = 95.144 atm