Osmosis Flashcards
What is osmosis?
Movement of water from a low concentration solution (hypotonic) to a high concentration solution (hypertonic), though a semi permeable membrane
What is osmotic pressure?
The amount of pressure that would need to be applied to the hypertonic side of a solution to stop inward flow of its pure solvent across a semi-permeable membrane
Does osmotic pressure cause movement of fluid until the solutions on either side of the membrane are completely isotonic?
No, movement will stop once osmotic pressure of the solution is reached, even if the solution is still relatively hypertonic. This is a colligative property as it is dependent on number of solute molecules rather than the nature i,e. The same number of moles glucose will exert the same as the same number of moles of nacl
What is hydrostatic pressure?
The pressure exerted by fluids e.g. water. For example the pressure exerted by plasma due to blood pressure.
What do we use to measure osmotic pressure and how do these work?
Osmometers. These use colligative properties such as reduced BP to measure osmolality. Urine or plasma are put in a tube in a cooled bath and the freezing temperature gives the osmolality
What equation do we use to calculate osmotic pressure?
Van’t hoff eqn
N (pie shape) = iMRT
I = VH factor
M = molarity
R = universal gas constant
T = temp in Kelvin
How does the osmolality fit into avogadros hypothesis?
In a 22.4L solution containing 1 mole of solute at STP.
Oncotic pressure = (1x8.31x273.15)/22.4 = 101.325kPa (1 bar)
Avogadro = 1 mole of gas exerts 1 atmosphere of pressure in 22.4L
How is a 1 molar solution different from a solution containing 1 mole?
1 molar = 1 mole per L
1 mole = just 1 mole regardless of volume
How much pressure would a 1 molar solution exert if you had 22.4L?
22.4 atmospheres
What is the osmotic gradient?
What is the plasma and intracellular K gradient?
Difference in osmotic pressure across a membrane. The gradient determines the rate that both sides become isotonic.
K gradient = 1:25
Does the osmotic gradient in humans ever become 0?
No as this would result in no movement of ions etc. and would result in death. It is prevented by using pumps etc.
What is reverse osmosis?
It is when pressure is applied to the high solute side of solution to allow the water to move up its concentration gradient to the area of low solute.
What can we use reverse osmosis for?
To produce drinking water from sea water. Need to apply 50 bar.
What is the osmotic pressure of seawater?
24 bar
What is an osmole?
The number of moles in a compound contributing to the overall osmotic pressure.
E.g. 1 mole of NaCL gives 2 osmolality whereas 1 mole of glucose gives 1
