P2 8 Chemical analysis

a single element/compound that hasn’t been mixed with another substance

• if another substance is mixed into a pure substance its boiling point will change • the purer the sample, the closer its boiling point to that of the pure substance

• a mixture designed to be a useful substance • components are mixed in measured quantities to ensure the formulation has the desired properties for its use • eg. paint, medicines, cleaning agents, alloys, fertilisers, fuels

• lit splint held at the mouth of the test tube containing the gas • burns rapidly with a squeaky pop if positive

• glowing splint inserted into the tube containing the gas • splint will relight if positive

• gas is bubbled through limewater • limewater turns cloudy/milky if positive

• damp blue litmus paper placed into the tube containing the gas • paper turns bleached white if positive

• separating (coloured) mixtures • testing purity - pure substance will produce one spot whereas compounds in a mixture will separate into different spots • identifying substances - compounds in a mixture identified using their Rf value

distance travelled by substance (ink) / distance travelled by solvent

• distance travelled by substance (ink) / distance travelled by solvent • measure distance between the starting pencil line and MIDDLE of the spot for substance • measure distance between starting+end pencil line for solvent • different compounds have different Rf values in a specific solvent • Rf used to identify compounds in a mixture

stationary - the paper -> less soluble substances mobile - the solvent moving up the paper eg. water -> more soluble substances

• less soluble substances: stronger attraction to the paper so spend longer in the stationary phase - move slowly+ travel a short distance up the paper • more soluble substances: stronger attraction to the water (solvent) so spend longer in the mobile phase - move quickly+ travel further up the paper

• draw horizontal pencil line 2cm from short edge of chromatography paper • use a pipette to put small spots of each ink on the pencil line (label under) • pour around 1cm3 water in beaker • suspend paper in beaker so bottom edge of paper dips in water • allow water to travel up paper (3/4) , remove paper then draw another line on the dry part beside where the water stopped • hang paper to dry fully • calculate distance travelled by water (solvent) and distances travelled by each ink (substances) • find Rf value of each ink spot (distance of substance / distance of solvent)