# Question d2b12

Jan 4, 2017

The molar mass of myoglobin is 8800 g/mol.

#### Explanation:

The formula for osmotic pressure ($\Pi$) is

$\textcolor{b l u e}{\overline{\underline{| \textcolor{w h i t e}{\frac{a}{a}} \Pi = M R T \textcolor{w h i t e}{\frac{a}{a}} |}}} \text{ }$

where

$M$ = molarity of the solution
$R$ = the Ideal Gas Constant
$T$ = the temperature of the solution

We can rearrange the above equation to get

$M = \frac{\Pi}{R T}$

Pi = 1.5 color(red)(cancel(color(black)("Torr"))) × "1 atm"/(760 color(red)(cancel(color(black)("Torr")))) = "0.001 97 atm"

$R = \text{0.082 06 L·atm·K"^"-1""mol"^"-1}$

$T = \text{(25 + 273.15) K" = "298.15 K}$

M = ("0.001 97" color(red)(cancel(color(black)("atm"))))/("0.082 06 L" color(red)(cancel(color(black)("atm·K")))·"mol"^"-1" × 298.15 color(red)(cancel(color(black)("K")))) = 8.07 × 10^"-5" color(white)(l)"mol/L"#

$\text{Moles of myoglobin" = "0.005 00" color(red)(cancel(color(black)("L"))) × 8.07 × 10^"-5"color(white)(l) "mol"·color(red)(cancel(color(black)("L"^"-1"))) = 4.03 × 10^"-7"color(white)(l) "mol}$

$\text{Molar mass" = "mass"/"moles" = (3.50 ×10^"-3" color(white)(l)"g")/(4.03 × 10^"-7" "mol") = "8700 g/mol}$

Note: I must be having a brain burp here. This is about half the recognized value for human, horse, and sperm whale myoglobin. Where is my mistake?