A saturated solution is made by dissolving 0.252 g of a polypeptide (a substance formed by joining together in a chainlike fashion some number of amino acids) in water to give 1.92 L of solution. The solution has an osmotic pressure of 3.69 torr at 25 °C. What is the approximate molecular mass of the polypeptide?
pi=3.69/760torr =.00485
M= m? r= .08205
T= 25+273.15= 298.15
m= pi/rt= .0000162 x 1.92=.0000312
.2521/.0000312
I get 8080.128 does that seem right?
The procedure looks ok but the numbers don't.You must be punching the wrong buttons.
The 0.00485 is really 0.004855 and I would round that to 0.00486
M (and that's M and not m) = 0.000198 x 1.92 = 0.000381
and molar mass is 0.242/0.000381 = ?
Check my work.
Let's break down the steps to calculate the approximate molecular mass of the polypeptide:
1. Calculate the moles of solute:
To start, we need to calculate the moles of solute (polypeptide) in the solution.
Moles of solute = mass of solute / molar mass
Given that the mass of solute is 0.252 g, we need to find the molar mass of the polypeptide.
2. Calculate the number of moles of solute:
To calculate the number of moles of solute, we use the formula:
Moles of solute = moles of solute / volume of solution
The solution has a volume of 1.92 L.
3. Calculate the osmotic pressure in atm:
We need to convert the given osmotic pressure from torr to atm.
Osmotic pressure (atm) = given osmotic pressure (torr) / 760 torr
The given osmotic pressure is 3.69 torr.
4. Calculate the approximate molecular mass:
Finally, we can calculate the approximate molecular mass of the polypeptide using the formula:
Molecular mass (g/mol) = moles / molar mass
We have the moles of solute from step 2, and we calculated the molar mass in step 1.
Now let's plug in the values and calculate:
1. Calculate the moles of solute:
Molar mass of the polypeptide = (0.252 g) / (moles of solute)
2. Calculate the number of moles of solute:
Moles of solute = (0.00485 atm) / (0.08205 L·atm/(mol·K) * 298.15 K)
3. Calculate the osmotic pressure in atm:
Osmotic pressure (atm) = 3.69 torr / 760 torr
4. Calculate the approximate molecular mass:
Molecular mass (g/mol) = (moles of solute) / (molar mass)
Now you can proceed with calculating the approximate molecular mass of the polypeptide using the values obtained in the steps above.
To find the approximate molecular mass of the polypeptide, you can use the formula for osmotic pressure:
Pi = (n/V)RT
Where:
Pi = osmotic pressure (in atm or torr)
n = number of moles of solute
V = volume of solution (in liters)
R = ideal gas constant (0.08205 L.atm/mol.K)
T = temperature (in Kelvin)
First, let's convert the osmotic pressure from torr to atm:
Pi = 3.69 torr / 760 torr/atm = 0.00485 atm
Now, rearrange the formula to solve for the number of moles of solute:
n = (Pi * V) / (RT)
n = (0.00485 atm * 1.92 L) / (0.08205 L.atm/mol.K * 298.15 K)
n ≈ 0.000162 mol
Next, calculate the molar mass of the polypeptide by dividing the mass of the solute by the number of moles:
Molar mass = mass / moles
Molar mass = 0.252 g / 0.000162 mol ≈ 1555.56 g/mol
So, the approximate molecular mass of the polypeptide is approximately 1555.56 g/mol.
It seems that there was an error in your calculation. The correct result is approximately 1555.56 g/mol, not 8080.128 g/mol.