eLFH - Solvents and Solutes

Question 1

Solution definition

Answer 1

A homogenous mixture of 2 or more substances

Question 2

Mixture / Suspension definition

Answer 2

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

Question 3

What gives water its strong capacity to act as a solvent

Answer 3

Its polar nature

Question 4

Why does water have such a high boiling point, melting point, heat of vaporisation and surface tension than would be predicted for small molecules

Answer 4

Hydrogen bonds (H bonds)

Question 5

What makes water molecules polar

Answer 5

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

Question 6

How many H-bonds can each water molecule form

Answer 6

4

Question 7

At what temperature is water most dense

Answer 7

4 degrees Celsius

Water becomes less dense when solid as ice

Water is only non-metallic substance to expand when solidifying

Question 8

Solutes which dissolve well in water

Answer 8

Ionic salts

Non-ionic but polar substances - sugars

Other molecules - ketones

Question 9

Solutes which do not dissolve well in water

Answer 9

Non-polar, lipophilic solutes

Eg oil

Question 10

Better solvent for non-polar lipophilic solutes

Answer 10

Benzene

Picture shows Benzene ring

Question 11

Hydration shells

Answer 11

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

Question 12

Clathrate formation

Answer 12

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

Question 13

Solubility definition

Answer 13

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

Question 14

Factors which affect solubility

Answer 14

Pressure

Temperature

Nature of solvent and solute (and intermolecular forces between them)

Question 15

Effect of pressure on solubility

Answer 15

Pressure does not greatly impact solubility of solid in liquid

Partial pressure of gas above solvent does impact its solubility (Henry’s law)

Question 16

Effect of temperature on solubility

Answer 16

Higher temp increases solid solubility in liquid

Higher temp reduces solubility of gas in liquid

Question 17

Clinical effect of gas solubility with temperature

Answer 17

Bubbles can form in intravenous fluid line that has gone through fluid warmer as dissolved air comes out of solution as temp increases

Question 18

How would be best to describe solubility such that it was not affected by temperature

Answer 18

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

Question 19

Colloid definition

Answer 19

Type of mixture or suspension

Made up of internal phase and external phase

Dispersed substance does not settle out under influence of gravity

Question 20

Internal phase of colloid

Answer 20

Small particles 1-1000 nm in diameter

Question 21

External phase of colloid

Answer 21

Solvent within which the internal phase is dispersed

Question 22

Emulsion definition

Answer 22

Colloidal system which is liquid in liquid - mixture of 2 or more immiscible liquids

(rather than solid in liquid or solid in gas)

Question 23

Emulsion formation

Answer 23

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

Question 24

Emulsion stabilisation methods

Answer 24

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

Question 25

Emulsion used clinically

Answer 25

Propofol

Emulsion of lipid soluble propofol in watery base

Question 26

Emulsifiers used in propofol

Answer 26

Egg and Soya lecithin

Question 27

Colligative properties definition

Answer 27

Physical properties of a solution that vary by the number of dissolved particles rather than by the identity of the solute

Question 28

Example of colligative properties

Answer 28

Change in boiling point or freezing point or vapour pressure of water with amount of salt or sugar dissolved

Question 29

Raoult’s Law

Answer 29

Overall vapour pressure of ideal solution depends on the vapour pressure of each component within the solution - which is in turn determined by mole fraction of each component

As concentration of solute increases, resultant vapour pressure of solvent must fall to keep total vapour pressure constant

Question 30

How does solute alter boiling point of solvent

Answer 30

Water boils when SVP reaches atmospheric pressure
Therefore at high altitude with lower atmospheric pressure, boiling point reduces to lower temperature

However adding solute reduces SVP of water, therefore higher temperature is needed to increase SVP to meet atmospheric pressure

That is why add salt to boiling water when cooking - increase temperature and speed up cooking

Question 31

How does solute alter freezing point of solvent

Answer 31

Liquids solidify by forming ordered matric like molecular structures

Dissolved solute disrupts this structure formation and freezing point is depressed

Used when rock salt spread on icy roads