# Calculate Molecular Weight of Polyethylene from Osmotic Pressure

• Chemistry
• mate1000
In summary, the formula for calculating the molecular weight of polyethylene from osmotic pressure is M<sub>w</sub> = RT/(V<sub>π</sub>ρ<sub>p</sub>), where M<sub>w</sub> is the molecular weight, R is the gas constant, T is the temperature, V<sub>π</sub> is the osmotic volume, and ρ<sub>p</sub> is the polymer density. The units used for the variables in the formula are M<sub>w</sub> (g/mol), R (J/mol*K), T (K), V<sub>π</sub> (m<sup>3</sup>/mol), and
mate1000
WOuld someone be able to give us a hand for this question, I am stumped.
Polyethylene is a synthetic polymer or plastic with many uses. 2.06 g of a polyethylene sample was dissolved in enough benzene to make 100 mL of solution, and the osmotic pressure was found to be 1.86 torr at 25oC. What is the molecular weight (g mol-1) of the polyethylene? (1 torr = 1 mm Hg, 1 atm = 760 mm Hg)
Cheers

How does osmotic pressure depend on the dissolved substances concentrations?

You have to make an attempt at the question - what relationships do you know about osmotic pressure and molecular weight?

## What is the formula for calculating the molecular weight of polyethylene using osmotic pressure?

The formula for calculating the molecular weight of polyethylene from osmotic pressure is Mw = RT/(Vπρp), where Mw is the molecular weight, R is the gas constant, T is the temperature, Vπ is the osmotic volume, and ρp is the polymer density.

## What units should be used for the variables in the formula?

The units used for the variables in the formula are as follows: Mw (g/mol), R (J/mol*K), T (K), Vπ (m3/mol), and ρp (g/cm3).

## How is osmotic volume determined in the calculation?

Osmotic volume is determined by measuring the change in volume of the solvent before and after adding the polymer. The difference in volume is the osmotic volume, which is necessary for calculating the molecular weight of polyethylene.

## What is the significance of calculating the molecular weight of polyethylene from osmotic pressure?

Calculating the molecular weight of polyethylene from osmotic pressure is important for understanding the properties and behavior of polymers. It can also be used for quality control in industrial processes, as well as for research and development of new polymer materials.

## Are there any limitations to using osmotic pressure for calculating the molecular weight of polyethylene?

Yes, there are limitations to using osmotic pressure for calculating the molecular weight of polyethylene. This method is most accurate for polymers with a narrow molecular weight distribution and may not be suitable for polymers with a wide range of molecular weights. Additionally, the presence of impurities or side reactions can affect the accuracy of the results. Other methods, such as gel permeation chromatography, may be more suitable for these cases.

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