the molar mass of an enzyme was determined by dissolving it in water and measuri
ID: 912184 • Letter: T
Question
the molar mass of an enzyme was determined by dissolving it in water and measuring the osmotic pressure at 293K via the height of the water column. the following data were obtained (picture);
Concentrations (mg/cm³): 3.221, 4.618, 5.112, 6.722.
Water heights (cm): 5.746, 8.238, 9.119, 11.990.
Plot an appropriate graph and determine the molar mass of the enzyme in kg/mol.
Explanation / Answer
=MRT
where
is the osmotic pressure,
R is the ideal gas constant (0.0821 L atm / mol K),
T is the temperature in Kelvin,
M is the molar concentration of the solute.
M = C / molar mass = C/Mx
=RTC/Mx
Mx = RTC/
From a plot C vs. you obtain the value C/ (it can be also calculated, see the table)
1 cm H2O = 98.07 Pa = 0.0009741 atm
Conc. C,
mg/mL
Conc. C,
g/L
,
cm H2O
,
atm
C/ ,
g/L.atm
1
3.221
3.221
5.746
0.005597
575.5
2
4.618
4.618
8.238
0.008025
575.5
3
5.112
5.112
9.119
0.008883
575.5
4
6.722
6.722
11.990
0.011679
575.5
5
Average value =
575.5
Mx = RTC/ =
= 0.0821 L atm / mol K x 293 K x 575.5 g/L.atm = 13 840 g/mol = 13.840 kg/mol
Conc. C,
mg/mL
Conc. C,
g/L
,
cm H2O
,
atm
C/ ,
g/L.atm
1
3.221
3.221
5.746
0.005597
575.5
2
4.618
4.618
8.238
0.008025
575.5
3
5.112
5.112
9.119
0.008883
575.5
4
6.722
6.722
11.990
0.011679
575.5
5
Average value =
575.5
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