Section 6 - Colligative Properties Flashcards
What do colligative properties depend on?
Number of solute particles in a solution
What is included in colligative properties?
- Osmotic pressure
- Vapor pressure lowering
- Boiling point elevation
- Freezing point depression
What is a one molar (1M) solution?
One gram-molecular weight of substance dissolved to a final volume of 1000 mL
What is a one molal (1m) solution?
One gram-molecular weight of substance dissolved in 1000 g of water
Is a molal solution temperature sensitive?
No
What is a one normal (1N) solution?
The equivalent weight (one gram-molecular weight/valence) of substance dissolved in water to a final volume of 1000 mL
What is normal saline?
0.9% solution of NaCl
When saline is w/ the fluid of a cell, is it hypo, hyper, or isotonic?
Isotonic
What is osmotic pressure?
The amount of pressure which must be applied to the more concentrated side to stop passage of solvent molecules
Solutions for injection should be made __tonic whenever possible
Isotonic
What does semi-permeable mean?
Only solvent molecules can pass through the membrane (not solute molecules)
In a biological system, what is the tonicity of the bathing fluid?
Isotonic to the fluid inside of the cells
What does Raoult’s law show?
The effect of solute concentration on vapor pressure
What is Raoult’s law and what does each value correspond to?
Pa = Pa0 (1 - xb)
- Pa = vapor pressure of solution
- Pa0 = vapor pressure of pure solvent
- Xb = mole-fraction of solute
- Xa = mole-fraction of solvent (Xa + Xb = 1)
What is the vapor pressure of pure water at 20 C?
17.54 mmHg
What is boiling point (with respect to pressure)?
Temperature at which vapor pressure of a liquid is equal o the external atmospheric pressure of 760 mmHg
What happens to vapor pressure when a non-volatile solute is added, and what does this mean for boiling point?
- Vapor pressure is lowered
- Solution must be brought to a higher temp than the pure solvent to reach the boiling point
What is freezing point (with respect to pressure)?
Temperature where solid and liquid phases of a solution are in equilibrium at a pressure of 1 atmosphere
What is the formula for boiling point elevation?
- Delta Tb = (Kb)(m)
- Tb = increase in temperature required
- Kb = proportionality constant
- m = molal strength of the solute
What is the boiling point proportionality constant for water?
0.515 C
What is the formula for freezing point depression?
- Delta Tf = (Kf)(m)
- Tf = lowering of freezing point
- Kf = proportionality constant
- m = molal strength of solute
What is the freezing point proportionality constant for water?
1.858 C
Identical molal solutions of non-electrolytes have the same _____
Colligative properties
How many grams of dextrose dissolved in 1000 g of water will produce a 0.1 molal solution?
19.8 g
How many grams of mannitol dissolved in 1000 g of water will produce a 0.1 molal solution?
18.2 g
How many grams of glycerin dissolved in 1000 g of water will produce a 0.1 molal solution?
9.2 g
Why are colligative properties different for identical molal electrolyte solutions?
Each ion will act as a particle, so the colligative properties will be a function of the degree of ionization
When in solution, how many particles will Na3citrate produce?
Four particles
What is a millimole?
1/1000 of the molecular weight in grams
What is the equivalent weight?
The molecular weight of the substance divided by the valence
What is milliequivalents related to?
Total number of ionic charges
What unit is used to expressed osmotic pressure?
mOsmol
What amount of dextrose will produce one mOsmol?
1 mmol b/c dextrose in a non-electrolyte
What will 1 mmol of NaCl be in mOsmol?
2 (assuming 100% ionization, will dissociate into 2 ions)
What happens to electrolyte solutions as concentration increases (with respect to dissociation and osmolarity)?
More interactions btwn solute particles, so electrolyte dissociation is less than 100%, so measured osmolarity will be less than calculated
What is the osmolarity of an isotonic solution?
275-320 mOsmol/L
What is the difference between osmolarity and osmolality?
- Osmolarity = milliosmoles of solute per litre of solution
- Osmolality = number of milliosmoles per kilogram of solvent
For which formulations are isotonic solutions better tolerated?
- Ophthalmic
- Nasal
- Vaginal
- Parenteral
How can you prepare isotonic solutions?
Using data derived from colligative properties of the solution
What temperature does serum freeze at?
-0.52 C
How can you determine how much of a substance dissolved in 1000g of water will give an isotonic solution?
- Use freezing point depression
- Know that serum freezes at 0.52 C
- Formula = (0.52 * MW) / (1.86 * i) = g of solute in 1000 g water
- i = dissociation factor
What can you determine from knowing that a solution of 55.5 g dextrose monohydrate in 1000 g of water has a freezing point depression of 0.52 C?
It is isotonic
What happens to degree of dissociation w/ increasing concentration?
Degree of dissociation decreases, so need to use a dissociation factor
What is the first step in making 100 mL of an isotonic solution of atropine sulfate 1%?
Determine how much the atropine contributes towards the tonicity of the solution
How will the tonicities compare of 2 solutions, each prepared w/ 1 gram-molecular weight divided by it’s i value and dissolved in 1000 g of water?
Tonicity will be the same
What is the i value for a substance that dissociates into 2 particles?
1.8
What is the i value for a substance that dissociates into 3 particles?
2.6
What is the i value for a substance that dissociates into 4 particles?
3.4
What method should be used to make an isotonic solution if the final product is to be buffered and what does this method include?
- Volume adjustment
- Determine the quantity of water needed to make an isotonic solution for a given amount of drug, followed by dilution w/ an isotonic solution to make up the volume
How do you do volume adjustment calculations?
Multiply weight of drug by its sodium chloride equivalent (E) = quantity of sodium chloride osmotically equivalent to weight per gram of drug
What is an easy way to make an isotonic solution?
Dissolve weight of drug * E in volume (mL) of water
Will adding together 2 isotonic solutions produce an isotonic solution?
Yes
