Chemical Analysis Freesciencelessons Flashcards
What is a pure substance?
Single element or compound that is not mixed with any other substance
How can you tell if a substance is pure?
It will have a specific fixed melting and boiling point
How can you tell if a substance is impure?
It melts and boils over a range of temperatures
Define formulation
A complex mixture that has been designed as a useful product
What are quantities like in a formulation?
Carefully measured components so products have the properties needed e.g. medicine
What type of process are all separation techniques?
Physical processes
Why are separation techniques physical processes?
They do not involve chemical reactions and no new substances are made
What does paper chromatography do?
Seperate substances based on their different solubilities
Summarise the chromatography practical.
Draw a pencil line near the bottom of a piece of chromatography paper, put dots of each colour on the line using a capillary tube,attach the paper to a rod and lower into a beaker of a small amount of solvent,the solvent will travel up the paper dissolving the ink which will travel up as well, draw a pencil line where the solvent reached and leave it to dry
What is the stationary phase of the chromatography practical?
Paper - as it doesn’t move
What is the mobile phase of the chromatography practical?
Solvent - as it moves up
How many spots appear for a pure substance?
One
How many spots appear for a mixture/impure substance?
Two or more
Why does paper chromatography work?
The chemicals in the mixture are attracted to the stationary phase to different extents
What does strongly attracted mean for the movement?
Won’t move up far
What does weakly attracted mean for the movement?
Will move further up
Why do we draw the starting line in pencil?
It is insoluble in the solvent therefore will not move up the paper
How can we determine which inks are in an unknown mixture?
The spots that line up with the unknown mixture are in the mixture
How do we measure Rf value?
Measure from the pencil line to the centre of each spot and the distance moved by the solvent to the new pencil line
What is the equation for Rf value?
Distance moved by substance / distance moved by solvent
What is the hydrogen test?
Remove the bung from the test tube and insert a burning splint, hydrogen burns quickly and produces a squeaky pop sound
What is the oxygen test?
Insert a glowing splint into the test tube and the splint will relight if its oxygen
What is the carbon dioxide test?
Use limewater in a test tube (aqueous solution of calcium hydroxide) and draw in some gas using a pipette,bubble gas through limewater and repeat until the limewater turns cloudy
What is the chlorine test?
Insert damp litmus paper into the test tube, chlorine gas will bleach the litmus paper white
