Chemistry revision 2 separation methods

Decanting

The pouring of a liquid from a settled solid
Used to separate liquid from undissolved solids quickly
E.g. sand from water

Filtration

Decanting can be used to separate components of a mixture prior to or with filtration
Often used to separate liquid or solution from insoluble solid
E.g. salt soluble in water but sand is insoluble, sand taken out with filter paper

Evaporation

recovery of a dissolved solid from a solution

crystallisation

depends on the components of a mixture having different solubilities in a selected solution
E.g. a mixture of salt and baking soda can be separated by dissolving in hot water and then cooling the resultant solution

Recrystallisation

often used to purify impure substances
E.g. sugar refining
1. impure substance dissolved in a minimum amount of solvent at high temp
2. hot mixture is filtered to remove insoluble impurities
3. filtrate is cooled, causing crystals of the pure substance to form
4. crystals can be filtered, leaving any impurities in the filtrate

Distillation

Used to purify liquids
Effective when mixtures have different boiling points
1 liquid evaporates

Fractional Distillation

separation of 2 or more liquids from a mixture
E.g. alcohol form wine
petrol, kerosene + oil from crude oil

Solvent extraction

Separate substances because of their different solubilities in 2 immiscible liquids
E.g. salt and iodine
1. dissolve mixture in water and add separating funnel
2. solvent is added and mixture is shaken
3. mixture settles salt will dissolve
4. 2 liquids separated by running lower layer through tap

Chromatography

Used to separate components in small quantities of mixtures
E.g. dyes or drugs
1. mixture is passed over inert substance
2. separation of components occurs because they cling to surface of inert substance
3. less absorbing components pass through

Ionic bond

Lattice structure
Form as a result of electrostatic attraction between anion and cation

ionic bond properties

Melting point
- high melting and boiling point due to high electrostatic force so lots of energy and thermal heat needed to break it
Brittleness
- brittle as it you move the lattice the positive will repel the positive and negative will repel the negative
Electrical conductivity
dont have mobile charge carriers in solid state but do in molten (liquid) state

Metallic bonds

Bond between 2 metals
formed by electrostatic attraction between delocalised electrons and the lattice of positively charged ions

Metallic bonding Properties

Melting point
- high melting point as there is a high electrostatic attraction between delocalised electrons and the +ve ions
Electrical Conductivity
- free mobile charge carriers - delocalised electrons that can carry charge
Thermal Conductivity
- good thermal conductors as electrons transfer Ek throughout the structure very quickly
Malleable + Ductile
- metallic bonds are non-directional so they can be bent and shaped easily

Covalent bonds

occurs between non metals - electrons shared
very strong bonds as they share electrons

Covalent molecular structures

small group of atoms bonded together
Properties
Melting point
- Low melting point as weak INTERmolecular forces between them (not INTRA)
Conductivity
- dont conduct electricity as they dont have mobile charge carriers
Malleable
- easy to form into shapes due to weak intermolecular force

Covalent network structures

continuing lattice structures bonded together
Properties
Melting point
- high melting point as large amount of energy required to break electrostatic attraction
Brittle
- strong bonds and wont change shapes
Conductivity
- only graphite conducts electricity as it is the only one with mobile charge carriers