# Calculate Molar Mass of Protein from Osmotic Pressure

• physicsss
In summary, to determine the molar mass of a certain protein, 1.00E-3 grams of the protein was dissolved in enough water to make a 1.00 mL solution. The osmotic pressure of this solution was found to be 1.12 torr at 25.0C. The molar mass of the protein can be calculated using the equation p = i M R T, where i is the van't Hoff factor and is likely to be 1 for proteins, and R and T are constants. This equation can be rearranged to solve for M, the molar mass of the protein.
physicsss
To determine the molar mass of a certain protein, 1.00E-3 grams of the protein was dissolved in enough water to make a 1.00 mL solution. The osmotic pressure of this solution was found to be 1.12 torr at 25.0C. Calculate the molar mass of the protein.

Yes ? And what do you want us to do ?

physicsss said:
To determine the molar mass of a certain protein, 1.00E-3 grams of the protein was dissolved in enough water to make a 1.00 mL solution. The osmotic pressure of this solution was found to be 1.12 torr at 25.0C. Calculate the molar mass of the protein.
I assume you want help in working out the molar mass. Where are your attempts first?

The Bob (2004 ©)

I tried using this equation: p = i M R T, but I have no idea what i is.

physicsss said:
I tried using this equation: p = i M R T, but I have no idea what i is.

i = moles of stand-alone stuff per mole of stuff (for lack of better words). for example, i for sulphuric acid is 3. i for potassium chloride is 2. i for acetic acid is 1 (weak acids do not dissociate).

Do you know what it is for protein?

Probably 1

i = van't Hoff factor. Roughly speaking, it measures the degree to which the ions dissassociate in solution. For example, the van't Hoff factor of NaCl is 2 since NaCl completely dissassociatesin water. Since most proteins don't ionize in water, n is probably 1.

i does not necessarily have to be an integer. For compounds that don't completely dissassociate, the van't Hoff factor is less than wht you would expect. The van't Hoff factor for HF for instance, is only a little bit more than 1 and not 2 since HF is a weak acid.

## 1. What is the purpose of calculating the molar mass of a protein from osmotic pressure?

The purpose of calculating the molar mass of a protein from osmotic pressure is to determine the average molecular weight of the protein. This information can be used to identify the type and structure of the protein, as well as its potential biological functions.

## 2. How is osmotic pressure related to the molar mass of a protein?

Osmotic pressure is directly proportional to the molar mass of a protein. This means that as the molar mass of a protein increases, so does its osmotic pressure. This relationship is due to the fact that larger molecules exert a greater pressure on a solution compared to smaller molecules.

## 3. What is the formula for calculating the molar mass of a protein from osmotic pressure?

The formula for calculating the molar mass of a protein from osmotic pressure is M = πRT/MRT, where M is the molar mass of the protein, π is the osmotic pressure, R is the gas constant, T is the temperature in Kelvin, and MRT is the molecular weight ratio of the protein.

## 4. What units are typically used for osmotic pressure and molar mass in this calculation?

Osmotic pressure is typically measured in units of atmospheres (atm) or kilopascals (kPa), while molar mass is usually expressed in grams per mole (g/mol). It is important to use consistent units in the calculation to ensure accurate results.

## 5. Are there any limitations to using osmotic pressure to calculate the molar mass of a protein?

Yes, there are some limitations to this method. Osmotic pressure measurements can be affected by factors such as temperature, pH, and ionic strength of the solution. Additionally, the protein must be in a pure and homogeneous state for accurate results. Other techniques, such as mass spectrometry, may be more precise for determining molar mass in certain cases.

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