Tutorial 2: Solubility Flashcards Preview

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Flashcards in Tutorial 2: Solubility Deck (10):
0

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

1

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

2

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

3

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

4

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

5

What factors are considered when choosing a cosolvent?

Log P value
Aqueous solubility
High or low dielectric constant?

6

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

Solubility increases with pH

7

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

Solubility decreases with pH

8

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

9

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