eLFH - Solvents and Solutes Flashcards
Solution definition
A homogenous mixture of 2 or more substances
Mixture / Suspension definition
Non homogenous mixtures where 2 or more substances are dispersed through each other but constituent parts retain their original identity
E.g more dense constituents still sink
What gives water its strong capacity to act as a solvent
Its polar nature
Why does water have such a high boiling point, melting point, heat of vaporisation and surface tension than would be predicted for small molecules
Hydrogen bonds (H bonds)
What makes water molecules polar
Covalent bonds hold hydrogen atom to oxygen atoms via shared pairs of electrons
Has non-linear molecular arrangement
Bent structure means hydrogen atoms maintain small net positive charge, and oxygen maintains small negative charge - makes it polar
How many H-bonds can each water molecule form
4
At what temperature is water most dense
4 degrees Celsius
Water becomes less dense when solid as ice
Water is only non-metallic substance to expand when solidifying
Solutes which dissolve well in water
Ionic salts
Non-ionic but polar substances - sugars
Other molecules - ketones
Solutes which do not dissolve well in water
Non-polar, lipophilic solutes
Eg oil
Better solvent for non-polar lipophilic solutes
Benzene
Picture shows Benzene ring
Hydration shells
Water readily dissolves salts despite electrostatic attractions between cations and anions
Because dipolar nature of water molecule enables formation of strong hydration shell to surround components of the salt
Clathrate formation
More complex hydration shell which forms around larger non-polar molecules
Electrical forces amongst the water molecules combine to surround the non-polar solutes in cage like structure
Solubility definition
Ability of a substance to dissolve in a solvent
Measure of maximum amount of solute that can dissolve per amount of solvent under specified temperature and pressure
Factors which affect solubility
Pressure
Temperature
Nature of solvent and solute (and intermolecular forces between them)
Effect of pressure on solubility
Pressure does not greatly impact solubility of solid in liquid
Partial pressure of gas above solvent does impact its solubility (Henry’s law)
Effect of temperature on solubility
Higher temp increases solid solubility in liquid
Higher temp reduces solubility of gas in liquid
Clinical effect of gas solubility with temperature
Bubbles can form in intravenous fluid line that has gone through fluid warmer as dissolved air comes out of solution as temp increases
How would be best to describe solubility such that it was not affected by temperature
Mass of solute in mass of solvent
(I.e 1% = 1g in 100g water rather than 100 ml water)
Volume of solvent may change with varying temperature whereas mass will not
Colloid definition
Type of mixture or suspension
Made up of internal phase and external phase
Dispersed substance does not settle out under influence of gravity
Internal phase of colloid
Small particles 1-1000 nm in diameter
External phase of colloid
Solvent within which the internal phase is dispersed
Emulsion definition
Colloidal system which is liquid in liquid - mixture of 2 or more immiscible liquids
(rather than solid in liquid or solid in gas)
Emulsion formation
Energy input through stirring, shaking or spraying is required to form the initial emulsion
Tend to revert to their component parts over time - more stable emulsions remain evenly dispersed for long periods of time
Emulsion stabilisation methods
Use of emulsifiers to stabilise emulsions
Eg. surfactants - surface active substances such as egg yolk
Surfactant binds electrostatically to surface of particles enabling particles to maintain position within emulsion
