The osmotic pressure exerted by a solution is equal to the molarity multiplied by the absolute temperature and the gas constant R. Suppose the osmotic pressure of a certain solution is measured to be 20.atm at an absolute temperature of 321.K. Write an equation that will let you calculate the molarity c of this solution. Your equation should contain only symbols. Be sure you define each symbol other than R.

20 atm / (R . 321 K . i) = M

Explanation:

Osmotic pressure is a colligative property which is determined by the solute.

Solutes over solutions, can increase the osmotic pressure which is calculated like this:

P = M . R . T

where P is pressure, M is molarity, R the Universal Constant Gases and T, the absolute Temperature. We also have to consider the Van't Hoff factor, i, numbers of ions dissolved. Ionic salts determine more osmotic pressure than organic compounds, where i = 1. Then, the complete formula is:

π =  M . R . T . i

To determine molarity, osmotic pressure divide all the terms:

20 atm / (R . 321 K . i) = M

R = 0.082 L.atm/mol.K

If you see all the units in R, they will be cancelled, so finally the answer will be mol/L, which is molarity. The i term has no unit!.

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