Question

Neatly present all calculations requested below.

You know that plasma is a solution, composed of many different solutes in water. Most of these solutes are NaCl (0.9%). But there are also proteins in plasma (Total protein=7g%), and albumin accounts for more than half of that protein. So, let's assume albumin's concentration in plasma is 4g%.

1) Compute the osmolalities for each substance, albumin and NaCl, in plasma.

Necessary information: NaCL molecular weight=58.5 g/mole. The molecule is formed by ionic bonds, and dissociates into 2 ions. Albumin molecular weight=70,000 g/mole. Albumin is composed of atoms which are covalently bonded, and do not dissociate. It is a fact that the osmotic pressure exerted by 1 osmolal (1 osmole/L) of solute is 19,300 mmHg; (that's the same as 1mOsmolal (1mOsmole/L) solute exerting 19.3 mmHg pressure).

2) Compute the osmotic pressure exerted by each of the substances, albumin and NaCl in plasma. Which substance is larger? There are more molecules of which substance in plasma? With the information, which substance exerts greater osmotic pressure in plasma, NaCl or protein?

"Colloid osmotic pressure" is the term given to the osmotic pressure exerted by protein.

Answer 1

Answer 1

Osmolarity =

number of mole of dissolved particle / number of litre of solution

Step one convert grams to mole:

NaCl - 0.9 gm% = 0.9gm/ 100 mel

Convert GM/ ml to gm/L

0.9gm/100 ml × 1000 ml

Now convert grams to mole - this achieve by dividing by the molecular weight

Therefore,

0.9gm/ 100 ml × 1000 ml × 1mole / 58.5 gm

Now, NaCl completely dissolved and gives rise to 1 Na+ and 1Cl- = 2 osmoles

Therefore,

0.9gm/100ml × 1000ml × 1mole /58.5 × 2 osmoles/ 1 NaCl

The amount of solution is 1L

Inserting all values in the formula, we get

Osmolarity =

0.9gm/100 ml × 1000 ml/ 1L × 1 mole/ 58.5 gm× 2 osmoles / 1 mole

Cancelling gms and mole and ml

0.9/100 × 1000 / 1 L × 1/ 58.5× 2 osmoles

= 0.308 osmole/ L

=308 mosmole/L

The osmolarity of 0.9% NaCL is 308 mosmole/L

Osmolarity for albumin 4gm% - please do remember albumin doesn't dissolve - 1 mole of albumin = 1 osmole

Inserting all the values in the formula we get

4g/ 100ml × 1000ml/ L× 1 mole / 70000 g × 1osmole/ 1mole

Cancelling the ml, g, mole

4/100 × 1000/L × 1/ 70000 × 1osmole

0.000571 osmole/L

0.571 mosmole/L ( 1 osmole = 1000 mosmoles)

Let us calculate the osmotic pressure

Formula for osmotic pressure is

iMRT

i = von hoff's factor

M = molar concentration of solution (mol/L)

R = ideal has constant

T= temperature in Kelvin's

Osmotic pressure for NaCL

First let's convert 0.9 gm % into mol/ L =

0.9gm/ 0.1 ml × 1/ 58.5 gm ×

The i for NaCl is 2 (as it completely dissolved)

R = 0.0821 LAtm/mol K

Convert temperature into Kelvin

37 + 273 = 310 K

Inserting all values in the formula

2 × 0.9g / 0.1 L ×1/58.5g × 0.0821 Latm/molK × 310K

Cancelling g , mole , K , L

2 × 0.9 /0.1 × 1/ 58.5× 0.0821 atm × 310

7.82 atm

7.82 atm is the osmotic pressure of NaCl

For albumin 4 gm% ( remember albumin doesnt dissociate so i = 1

Using the same formula

1 × 4 g / 0.1 L × 1mole/ 70,000 g × 0.082 L atm/ molK × 310 k

1 × 4/0.1 × 1/70000 × 0.082 Atm × 310

0.014 atm

The oncotic pressure of albumin is 0.014 atm

The osmotic pressure of sodium is higher than that of albumin

There is more sodium (140 mmol/L) than albumin in blood

Osmotic pressure is directly related to molar concentration in this example the molar concentration of NaCL was higher that albumin. Therefore the osmotic pressure of NaCl is high