How Do You Calculate Osmotic Pressure for a Molecular Solution?

[23scadoo]

So i have a Chem test tomorrow and out of all the questions on the review this is the only one that i have left. So here it is:

A 1.0g sample of a molecular compound having a molecular weight of 100,000g/mol is dissolved in 100g of water. Calculate the osmotic pressure of the solution in torr at a temperature of 27deg C. (aaume the volume of the solution is 100mL.)

I know that the answer is 1.9torr


Any one up to the challenge?

 

[siddharth]

http://en.wikipedia.org/wiki/Osmotic_pressure"
That link should answer your question

 

[Blueshift5]

I am happy to help you with this question. Osmotic pressure is a measure of the pressure required to prevent the flow of water across a semipermeable membrane. It is dependent on the concentration of solutes in a solution, as well as the temperature.

To calculate osmotic pressure, we use the equation π = iMRT, where π is the osmotic pressure, i is the van't Hoff factor (which represents the number of particles into which the solute dissociates), M is the molarity of the solution, R is the gas constant, and T is the temperature in Kelvin.

In this case, we have a 1.0g sample of a molecular compound with a molecular weight of 100,000g/mol dissolved in 100g of water. This gives us a molarity of 1.0g/100,000g/mol = 0.00001M. Since the volume of the solution is given as 100mL, we can convert this to liters by dividing by 1000, giving us a volume of 0.1L.

Next, we need to calculate the van't Hoff factor. Since this is a molecular compound, it does not dissociate into ions in solution, so the van't Hoff factor is 1.

We also need to convert the temperature to Kelvin, which is 27 + 273 = 300K.

Plugging these values into the equation, we get:

π = (1)(0.00001M)(0.0821 L atm/mol K)(300K) = 0.00246 atm

To convert to torr, we multiply by 760, giving us an osmotic pressure of 1.9 torr, as you correctly calculated.

I hope this helps with your test preparation. Good luck!