separating substances Flashcards
what is it called when a substance goes straight from a solid to a gas
sublimation
what is it called when a substance goes straight from a gas to a solid
deposition
what is a physical change
physical changes can be reversed as the particles do not change but the arrangement and movement and amount of stored energy does, the chemical properties stay the same
what is lost when a solid is heated
attractive forces
how do tell apart the melting point of an impure substance and a pure substance
pure has a sharp clear melting point, a mixture doesn’t
solution =
solute + solvent
what is a mixture
contains elements/compounds that aren’t chemically bonded, doesn’t have a fixed composition and can be separated through physical processes
why will a pure substance have a sharp melting point
because it has the same composition in every part of the substance, its physical properties are the same all throughout it
how do filters separate mixtures
they let smaller pieces of liquids through but trap insoluble substances
what are some examples of filters
coffee maker, cars, vacuum cleaners, air conditioning
what is a saturated solution
contains the maximum amount of solute that can be dissolved by the solvent at that temperature
how do salt crystals form from a saturated solution
if more water evaporates or the solution cools
what is a filtrate and residue
filtrate = the solvent and solute that pass through the filter's fine holes residue = bits of insoluble substances that cannot fit through the tiny holes in the filter paper
what are some bad things that could come from overheating the filtrate during crytalisation
hot crystals may spit out
crystals may change chemically
what’s the difference between a risk and a hazard
hazard = something that could cause harm risk = chance of a hazard causing harm
why does the temperature stay the same at the melting and boiling point?
the substance is still being heated but the added energy is making the particles break away from their fixed arrangement
in paper chromatography, what ink would be carried further up the paper
the more soluble ink molecules
why does paper chromatography work
because the different inks in a mixture all dissolve to different extents in the solvent, the more attracted the ink is to the paper the less high it will travel up the paper leading the different inks to spread out (separate)
what is the mobile phase and the stationary phase in paper chromatography
paper = stationary phase solvent = mobile phase
what number is Rf value always below
1
how do you calculate Rf value
distance travelled by spot / distance travelled by solvent
what can paper chromatography be used for
identifying substances at crime scenes
distinguishing between pure and impure substances
what does distillation do
makes a substance pure
how do simple distillation and fractional distillation differ
simple separates a liquid from minerals and dissolved or solid substances
fractional separates two liquids that have different boiling points
