Chapter 2 - Separation Techniques Flashcards
What is the difference between a pure and impure substance?
- pure substance has a fixed melting and boiling point
- impure substances melt and boil over a range of temperatures
- impurities lower the mp of a pure substance while increasing the bp of a pure substance
What are the separation techniques for solid-solid mixtures?
magnetic separation, sublimation and dissolution
What are solids that sublime?
iodine, ammonium chloride, dry ice, and naphthalene (mothballs)
What are the separation techniques for solid-liquid mixtures?
filtration, evaporation to dryness, crystallisation and simple distillation
for filtration, what is the solid remaining on the filter paper called and the liquid that passes through the paper called?
residue, filtrate
can all soluble substances use evaporation to dryness?
no
What is crystallisation? What is the procedure for crystallisation?
process of obtaining a pure solid from its saturated solution. Heat the solution until it becomes saturated (not all water is evaporated). allow the saturated solution to cool at r.t.p and crystals of the solid will form. mixture is then filtered, washed with cold distilled water, then dried by pressing them between sheets of paper.
What are the separation techniques for liquid-liquid mixtures?
fractional distillation and chromatography
how to calculate Rf value?
distance moved by substance / distance moved by solvent (x / y)
What is chromatography for?
separate 2 or more substances which have different solubilities in the same solvent
what is the most commonly used solvent in paper chromatography?
ethanol and water
how to analyse colourless substances in chromatography?
apply a locating agent. it reacts with the colourless substances to form coloured spots
