Flashcards in Lecture 8 Deck (42):
What are the solution mecanisms?
hydrogen bond formation
acid base reactions
breaking covalent bonds
what is the dielectric constant?
the extent of the material to store electric charge.
basically gives an indication of the polarity of the molecule
e.g. dielectric constant of water is 80. it is the highest so has the ability to break the bonds between ionic molecules.
whereas chloroform and benzene have low dieletric constants so are poor at solvating ionic salts
What is the relationship between dielectric constant and polarity?
Dielectric constant is proportional to polarity. So as dielectric constant decreases, the polarity will decreases, thus water solubility will also decrease
Can water dissolve organic and inorganic salts?
What can a solvent with a smaller DC dissolve?
non polar substances
How is dipole interaction relevant to solvation?
polar solvents are capable of solvating molecules and ions through dipole interaction forces
What is a dipole interaction?
an attraction between a partially negative portion of one molecule to the partially positive portion of another molecule nearby
What does the solute like to compete for?
the bonds of the solvent molecules
What does the dipole depend on?
the structure of the molecule.
If the molecule is symmetrical, the vector of the dipole moment will cancel out and there will be no resultant dipole.
Most polar solvents dissolve by the formation of what type of bonds?
these are interactions between H and electronegative atoms like F, O and N
It tends to form an electrostatic unit with the most electronegative part
What do polar solvents tend to do to strong acids and bases?
they tend to break the covalent bond of strong acids and bases
How can polar solvents break covalent bonds of strong acids and bases?
polar solvents are amphiprotic in nature so they can act as an acid or a base.
e.g. water with HCl can form H+ ions
Water with amine can from OH- ions
Why do weak acids only have partial solubility in water?
They do not completely ionise water. They are only partially soluble due to Hydrogen bonds.
What happens to solubility as ionisation increases?
solubility will decrease
What is the name given to the principle that describes the behaviour of reactions at equilbrium?
le chatelier's principle
What are the 3 main types of solutions in pharmaceutics?
1. gases in liquids,
2. liquids in liquids
3. solids in liquids
What are examples of a solution of gases in liquid?
common examples: carbonic beverages/fizzy drinks
pharmaceutical examples: ammonia water and effervescent preparations containing CO2
What is the solubility of the gas in liquid?
it is the concentration that is dissolved when it is in its equilibrium
What are the main factors that affect the solubility of gases?
addition of salts
what law shows the effect of pressure?
Henry's law. Which states that the solubility of any gas is directionally proportional to its partial pressure
What is partial pressure?
the total pressure above the solution - the vapour pressure of the solvent
What kind of solution do henry's law apply to?
very dilute solutions, when there is no chemical reaction.
What does a higher solubility coefficient value mean?
less pressure is required to dissolve the gas
Why is a cork wired on a bottle of champagne?
in the champagne, fermentation still continues in the bottle. CO2 is produced in this fermentation process which creates more pressure so if the cork is not wired, it will blow off the top
How can pressure affect deep sea diving?
When you are diving, there is a pressure exerted on you. during your time in the water you take up compressed gas so N tends to dissolve more.
However you resurface more rapidly than the pressure can decrease. This causes solubility of N to decrease so it tries to escape
this can cause a lot of pain and is dangerous
What is the effect of temperature on the solubility of a gas
as temperature increases, solubility of gas decreases due to gas expansion.
an increase in temperature increases the kinetic energy of the molecules. This will cause gases to escape rather than remain in the solvent.
Why does fizzy drink not taste as good after a while at room temperature?
At room temperature the solubility of CO2 decreases so it escapes as bubbles.
The fizzy drink will no longer taste as good
How should a solution with a high Vapour pressure e.g. ethyl nitrate be opened?
it should be immesred in ice or cold water before opening to ensure the temperature and pressure of the gas is controllable.
What causes a decreased solubility of the gas when adding an electrolyte?
the salting out effect
Why does salting out occur?
There is a greater affininty of the electrolytes towards the water molecule resulting in weakness of the gas solvent interactions.
This reduces the aqueous environment next to the gas molecule so the gas salts out
What effect does a chemical reaction have on solubility of the gas?
some gases like HCl, ammonia and CO2 deviate.
This causes a chemical reaction between the gas and solvent which increases the solubility
What is a liquid in liquid solution?
a preparation of pharmaceutical solutions which involve the mixing of 2 or more liquids
what are hydroalcoholic solutions?
solution formed from the mixing of alochol and water
what are aromatic waters?
solutions formed by the mixing of oils and water
what are spirits?
solutions formed by the mixing of volatile oils and alcohols
How can liquids in liquids solutions be categorised?
depending on their solubility
What are complete miscible solutions?
where two liquids are able to mix well in all proportions.
Means that adhesive forces > cohesive forces
and that there are no solubility problems for the pharmacist
What are partially miscible solutions?
where you attempt to mix 2 liquids but will form 2 layers,
This is due to the attraction between one of the liquids being much more stronger than the other
These type of systems can be changed with temperature
What is the critical temperature?
the temperature where a partially miscible system will become homoegenous
What is the upper critical temperature?
where the 2 liquids are miscible in all proportions
what is the lower critical temperature?
the temperature below where the 2 liquids are miscible in all proportions