chem prelim Flashcards
heterogeneous mixture
the constituents are not uniformly mixed throughout the mixture, eg water and oil
homogenous mixture
constituents are uniformly mixed meaning mixed the same throughout the mixture eg solution
aqueous form
when dissolved in water
pure substance
only homogenous cannot be separated into two or more substances by physical means, fixed composition and same properties
mixture
can be separated into two or more pure substances, may be homogenous or heterogenous, variable properties reflect parts that make it up
separate substances of different particle sizes
sieving
separating mixture of solids and liquids
filtration, if particles of solid are very coarse or dense use sedimnetation(solids settle at bottom of container) or decantation( carefully pouring off the liquid and leaving the solid undisturbed at the bottom of container)
separating dissolved solids from liquid if only want solid
evaporation, if only want solid
separating dissolved solid from liquid if want both liquid and solid
crystallisation(slower evaporation)
separate two or more liquids from one another
distillation(process of evaporating then condensing gas back into liquid in separate apparatus so liquids are separated) only if boiling points differs by at least 40 or 50 celsius
if the liquids are close in boiling point use
fractional distillation
immiscible liquids
do not mix due to density and must be separated using a separating funnel
steps of gravimetric analysis
dissolve same mole if not already in solution, adjust ph so that proper precipitate forms and to prevent formation of others, add chemical that favours precipitating material you want, filter solution, dry precipitate, weigh the precipitate
percentage composition
mass of one substancex100 on mass of total sample
pure substance has
characteristic colour