P2 8 Chemical analysis Flashcards
define pure substance
a single element/compound that hasn’t been mixed with another substance
describe how to identify the purity of a substance using boiling points
- 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
define a formulation +examples
- 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
describe the test for hydrogen
- lit splint held at the mouth of the test tube containing the gas
- burns rapidly with a squeaky pop if positive
describe the test for oxygen
- glowing splint inserted into the tube containing the gas
- splint will relight if positive
describe the test for carbon dioxide
- gas is bubbled through limewater
- limewater turns cloudy/milky if positive
describe the test for chlorine
- damp blue litmus paper placed into the tube containing the gas
- paper turns bleached white if positive
state uses of chromatography (3)
- 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
state equation for calculating the Rf of a compound in a solvent from chromatography
distance travelled by substance / distance travelled by solvent
describe what the Rf value of a compound in chromatography is
- ratio of distance travelled by substance to distance travelled by solvent
- measure the distance between the starting pencil line and (MIDDLE of the spot / ending solvent pencil line)
- different compounds have different Rf values in a specific solvent
- Rf used to identify compounds in a mixture
define stationary+mobile phase in chromatography
stationary - the paper
-> less soluble substances
mobile - the solvent moving up the paper
-> more soluble substances
describe how to identify more soluble substances in chromatography
- 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 solvent so spend longer in the mobile phase - move quickly+ travel further up the paper
describe steps for chromatography RP
