Pure substance =
Something that only contains one compound or element throughout (not mixed with anything else)
Test purity of sample by measuring its ….. and comparing it with the pure substance’s - the closer the measured value is to the actual value, ….
Melting or boiling point
The purer the sample
Formulations are …
Examples =
Useful mixtures with a precise purpose made by following a formula
In paint = Pigment, solvent, binder (resin), additives
Formulations particularly important in the ….. - for example:
Pharmaceutical industry
Changing formulation of a pill = deliver drug to correct part of body, right concentration, consumable, shelf life
Test for chlorine
Chlorine gas bleaches damp blue litmus paper (turns white)
Test for oxygen
Oxygen relights a glowing splint when placed in the gas
Test for carbon dioxide
Bubbling carbon dioxide through limewater (calcium hydroxide) causes solution to turn cloudy
Test for hydrogen
Burning splint at open end of test tube containing hydrogen you will hear a ‘squeaky pop’ sound
Two phases in chromatography :
A mobile phase - molecules can move (always a liquid or gas)
A stationary phase - molecules can’t move (solid or thick liquid)
Phase movement in chromatography
The mobile phase moves through the stationary phase and anything dissolved in the mobile ohase moves with it
The chemicals that spend more time in the mobile phase in chromatography ….
Will move further though the stationary phase
Components of mixture will normally separate through the …. As long as all components …..
Stationary phase
Spend different amounts of time in the mobile phase
Separated components form ,… - only pure substances have …
Spots
One spot
In paper chromatography
The stationary phase =
The mobile phase =
The chromatography paper
The solvent (eg ethanol or water)
Amount of time molecules spend in each phase depends on: 2x
How soluble they are in the solvent
How attracted they are to the paper
(High solubility = less attracted to paper = more time in mobile phase = carried further up the paper)
Rf value is the ….
Ratio between the distance travelled by the dissolved substances and the distance travelled by the solvent
Calculate the Rf value by using the formula=
Rf = distance travelled by substance (dot) / distance travelled by solvent (solvent front line)
If using chromatography to see if a substance is present in the mixture, …
You run a pure sample of that substance alongside the unknown mixture and if the Rf values of the reference and one of the spots in the mixture match, the substance may be present
Rf value is dependent on the ….
Solvent used
Paper chromatography
If you test both the mixture and the reference in a number of different solvents and the Rf values are all very similar, ….
It is likely the reference compound is present in the mixture
Test for anions (…..) often give ….
Negative ions
Precipitates
Test for carbonates (CO3 2- ions)
Use dropping pipette to add a few drops of dilute acid to test tube with substance
Connect test tube with test tube containing limewater - if carbonate ions present, carbon dioxide released in reaction + will turn limewater cloudy when bubbled through it
Test for sulfates (SO4 2- ions)
Use dropping pipette to add a couple drops of dilute hydrochloric acid followed by a couple drops of barium chloride solution (BrCl2) to a test tube containing mystery solution
If sulfate ions present - a white precipitate of barium sulfate will form
Test for halides (Cl-, Br-, I-)
Add a couple drops of dilute nitric acid (HNO3) followed by a couple drops of silver nitrate solution (AgNO3) to mystery solution
Chloride = white precipitate of silver chloride
Bromide = cream precipitate of silver bromide
Iodide = yellow precipitate of silver iodide
