Tutorial 2: Solubility Flashcards Preview

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Flashcards in Tutorial 2: Solubility Deck (10):

What is solubility?

The extent to which dissolution proceeds under a given set of environmental conditions

The maximum amount of solute that will dissolve in a given quantity of solvent at a given temperature


How does the solute interact with the solvent? (simple rule)

A solute dissolves best in a solvent with similar chemical properties

I.e. Like dissolves like


What are the solvation mechanisms for polar solvents?

Dielectric constant (this is essentially a measure of polarity)
Acid base reactions and breaking covalent bonds
Hydrogen bond formations
Dipole interactions


How is polarity assessed?

For solutes and solvents (solids, liquids) they can be assessed using a logp value.
Low log p = polar

For solvents (liquids) they can be assessed using the dielectric constant
High DC = polar

For surfactants polarity is assessed using an HLB value
High HLB = polar


What factors affect aqueous solubility?

Temperature (increased temp increases solubility in endothermic dissolution. This is the reverse for an exothermic dissolution)

Hydrophobicity (like dissolves like)

Acid base properties / pH

Crystalline form of the drug

Ionisation (ionised form have a higher solubility)

Surface area (smaller particle size = more SA:volume ratio = increased solubility)

cosolvents/ mixed solvent systems

Number of Carbon atoms (increased C decreases solubility)

Branching of structure (reduced molecular volume increases solubility)

Functional groups like CH, OH, NH


What factors are considered when choosing a cosolvent?

Log P value
Aqueous solubility
High or low dielectric constant?


What is the relationship between solubility and ph of an acidic drug?

Solubility increases with pH


What is the relationship of solubility and pH of a basic drug.

Solubility decreases with pH


What is an elixir?

Sweetened aromatic solution of alcohol serving as a vehicle for medicines

Solvent frequently contains a high proportion of ethanol and syrup

Other solvents like glycerol are also sometimes used


What is invert syrup?

Mixture of glucose and fructose prepared by hydrolysing 66.7%w/v in a solution with sucrose with suitable mineral acids like HCl

The solution is then neutralised using sodium bicarbonate or calcium

The degree ofinv ersion is usually 95% at least