chapter 3 - separation

Página 1

LIQUID IS SOLVENT , SOLUTE ARE SOLIDS THAT DISSOLVE IN SOLVENT

Filtration - separate a liquid from an insoluble solid

residue - insoluble solid

filtrate - the liquid passes through pores

decanting - careful pouring of liquid to leave insoluble solid at the bottom of the container

evaporation&dryness - obtain soluble solid

* if the solid is thermally stable ( don't decompose ) , solution is heated to dryness , solid remain as crystalline residue after the solvent has

evaporated

crystallisation

* if the solid is not thermally stable it will decompose

during crystallisation , water is removed to heat the solution to obtain hot saturated solution, when its cooled the dissolved solids will become pure

crystals . crystals can be filtered off and dried by pressing them between sheets of filter paper.

strong heating is often used when evaporating solvent , but it will cause some substances to decompose

during evaporation , some soluble impurities might be left together with solute , thus outcome of solute might not be pure.

distillation - to separate solvent from solution

during distillation , solution is heated , when it boils , solvent turns into vapour and leaves flask, hot vapour is then cooled in the condenser and condenses back into liquid and collected as distillate

!! this ensures that the coldest part of the condenser is just before any uncondensed vapour escapes , the jacket is completely filled with water

fractional distillation - to separate 2 more miscible liquids w diff boiling pt

> the liquid with lower boiling point will distil over first to condenser

> fractionating column is used to increase surface area for vapour to condense

> so the liquid with higher boiling point condense along the F.C and re-enter round bottom flask

separating funnel

> to separate 2 or more immiscible liquids

> denser liquid is at the bottom of the funnel

sublimation

> separate substance that sublime from one with high melting point

paper chromatography

- separate 2 or more substances or identify components in a mixture

separation of components

>components in the mixture dissolve in the solvent

> pencil lead contains carbon that is insoluble in water thus it will not affect chromatogram

> the start line is above the solvent , because is to prevent the ink from dissolving in the solvent without being separated

> spots must be small if not the components will overlap ---> unclear results

> cannot measure distance from the starting line to solvent front and Rf value cannot be determined

Rf= dist by component / dist by solvent front

colourless substances - locating agent is used as it is a chemical that reacts with substances to form visibly coloured products

Testing for purity

> if substances are pure , it would melt / boil at a fixed constant temp and there would only be a single spot

> if substances are impure , the substance would melt / boil over a range of temperature and there would be 2 or more spots