A protein has been isolated as a salt with the formula Na20P (this notation means that there are 20 Na+ ions associated with a negatively charged protein P20−). The osmotic pressure of a 10.0 mL solution containing 0.207 g of the protein is 0.295 atm at 25.0°C. (a) Calculate the molar mass of the protein from these data. g/mol (b) Calculate the actual molar mass of the protein.

Respuesta :

Answer:

a) 36,051.81 g/mol is the molar mass of the protein.

b) The actual molar mass of the protein is 757,087.96 g/mol.

Explanation:

Osmotic pressure of the solution = [tex]\pi = 0.295 atm[/tex]

Temperature of the solution , T= 25.0°C=25.0+273 K=298 K

Concentration of solution = C

van't Hoff factor = 20 +1 = 21

[tex]\pi =iCRT[/tex]

[tex]C=\frac{\pi }{iRT}=\frac{0.295 atm}{21\times 0.0821 atm L/mol K\times 298 K}[/tex]

[tex]C=0.0005742 M[/tex]

Moles of protein = n

Volume of solution = V = 10.0 mL = 0.010 L

[tex]C=\frac{n}{V(L)}[/tex]

[tex]n=0.0005742 M\times 0.010 L=5.742\times 10^{-6}mol[/tex]

Mass of  protein = 0.207 g

Molar mass of protein = M

Moles of protein(n) = [tex]\frac{0.207 g}{M}[/tex]

[tex]M=\frac{0.207 g}{5.742\times 10^{-6}mol}=36,051.81 g/mol[/tex]

36,051.81 g/mol is the molar mass of the protein.

b)

Actual molar mass of protein = M'

van't hoff factor = 21

[tex]i=\frac{M'}{M}[/tex]

[tex]M'=21\times 36,051.81 g/mol=757,087.96 g/mol[/tex]

The actual molar mass of the protein is 757,087.96 g/mol.

A) The molar mass of the protein from these data is; 1725 g/mol

B) The actual molar mass of the protein is; 36225 g/mol

Molar Mass Calculations

We are given;

  • Osmotic pressure; π = 0.295 atm
  • Mass of protein = 0.207 g
  • Volume of solution = 10.0 mL = 0.01 L
  • Temperature = 25.0 °C = 298.15 K

A) Formula for osmotic pressure is;

π = MRT

Where;

π is osmotic pressure

M is the molarity

R is the gas constant = 0.08206 L.atm/k/mol

T is the temperature.

Thus;

M = π/RT

M = 0.295/(0.08206 * 298.15)

M = 0.012 M

Molar mass = mass/(molarity * volume)

Molar mass = 0.207/(0.012 * 0.01)

Molar mass = 1725 g/mol

B) Since we are given 20 sodium ions, then Van't Hoff factor will be; i = 20 + 1 = 21

Formula for i is;

i = actual molar mass/observed molar mass

actual molar mass = 21 * 1725

Actual molar mass = 36225 g/mol

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