# Calculate Protein Molar Mass Using Osmotic Pressure | Homework Example"

• Qube
In summary, the problem involves finding the molar mass of a protein based on its osmotic pressure in a solution. Using the given information, the molar mass is calculated by dividing the mass of protein (35g) by the molarity of the solution (5.37 * 10^-4 moles/liter). This results in a molar mass of approximately 65,142 g/mol. Additionally, the same method can be applied to a different problem with different quantities of protein and water, as long as the units are consistent.
Qube
Gold Member

## Homework Statement

A solution is prepared by dissolving 35.0 g of a protein in enough water to make up 1.0 L in volume. If the osmotic pressure of the solution is found to be 10.0 mm Hg at 25 C, the molar mass of the protein will be closest to:

## Homework Equations

Osmotic pressure = MRT

## The Attempt at a Solution

Pressure is expressed in atm, so 10/760 = 0.013 atm = M(0.0821)(25 + 273 K)

The molarity = 5.37 * 10^-4 moles/liter.

Now, we are given that there are 35 grams of protein per 1 liter of water in the problem.

(35g/L)/(5.37 * 10^-4 moles/liter) = molar mass of the protein, since molar mass is mass/moles.

The units being divided are (grams/liter) and (moles/liter). This equals:

Grams/liter * (liters / moles)

The liters cancel out, and we get grams / mole.

Question:

1) I'm fairly confident my work is correct and my answer is similarly correct.

2) However, if this problem were to be written, say, there are 70 grams of protein in enough water to make up 2.0 L in volume, I would have to do this, right?

(70 grams / 2 liters)/molarity of the solution? Because grams/liters divided by moles/liter is equivalent to grams/liters * liters/moles and the liters cancel out and we get grams/mole.

And if the problem were to state 70 grams / 2 liters I would be erroronus to perform 70 grams / molarity, since there are 2 LITERS of water, right? Doing this would be assuming there were only 1 liter of water.

Typically if units work, result is OK. That's what the units are for.

1 person

## 1. What is osmotic pressure and how does it relate to protein molar mass calculation?

Osmotic pressure is the pressure that must be applied to a solution to prevent the flow of water across a semipermeable membrane. This pressure is directly proportional to the concentration of solute particles in the solution. In the context of protein molar mass calculation, osmotic pressure is used to determine the molecular weight of a protein by measuring the change in pressure caused by the addition of the protein to a solution.

## 2. What are the steps involved in calculating protein molar mass using osmotic pressure?

The first step is to prepare a solution with a known concentration of the protein. Then, measure the osmotic pressure of the solution using an osmometer. Next, add the protein to the solution and measure the new osmotic pressure. Finally, use the change in osmotic pressure and the known concentration of the protein to calculate the protein's molar mass using the van't Hoff equation.

## 3. Can osmotic pressure be used to calculate the molar mass of any protein?

In theory, yes, osmotic pressure can be used to calculate the molar mass of any protein as long as the protein does not alter the properties of the solution or interact with the semipermeable membrane. However, in practice, some proteins may not be suitable for this method due to factors such as solubility, stability, and aggregation.

## 4. What are some limitations of using osmotic pressure for protein molar mass calculation?

One limitation is that the protein must be in a monomeric form for accurate results, as aggregates or oligomers can affect the osmotic pressure of the solution. Additionally, the presence of impurities or other substances in the solution can also affect the accuracy of the measurement. Lastly, osmotic pressure measurements can be affected by temperature, so it is important to control for this factor during the experiment.

## 5. Are there any alternative methods for calculating protein molar mass?

Yes, there are other methods for determining protein molar mass, such as mass spectrometry, gel electrophoresis, and size-exclusion chromatography. Each method has its advantages and limitations, and the choice of method will depend on factors such as the type of protein, sample availability, and the desired level of accuracy.

• Biology and Chemistry Homework Help
Replies
1
Views
2K
• Biology and Chemistry Homework Help
Replies
10
Views
3K
• Biology and Chemistry Homework Help
Replies
4
Views
3K
• Biology and Chemistry Homework Help
Replies
8
Views
2K
• Biology and Chemistry Homework Help
Replies
14
Views
2K
• Biology and Chemistry Homework Help
Replies
3
Views
1K
• Biology and Chemistry Homework Help
Replies
3
Views
2K
• Biology and Chemistry Homework Help
Replies
2
Views
2K
• Biology and Chemistry Homework Help
Replies
1
Views
11K
• Biology and Chemistry Homework Help
Replies
2
Views
8K