chemical analysis Flashcards
what is a pure substance?
a single element/single compound
what is a mixture?
a combination of two or more substances that are not chemically combined
what is a formulation?
a mixture that has been designed for a specific purpose eg paint
what is the MP/BP of pure substances?
a single defined temperature
what is the MP/BP of mixtures?
melts/boils over a range of temperatures
how would you test purity?
test the melting or boiling point- if it is exact it is pure.
how big is a nanoparticle?
1-100nm
how are nanoparticles useful in formulations?
you can use less to the same effect (high surface area to volume ratio)
what is the purpose of chromatography?
used to separate substances and provide information to help identify them
describe the steps of chromatography (4)
- a pencil line is drawn on chromatography paper and spots of the sample are placed on it (pencil is used for this as ink would run into the chromatogram along with the samples)
- the paper is then lowered into the solvent container, making sure that the pencil line sits ABOVE the level of the solvent so the samples don’t wash into the solvent container
- the solvent travels up the paper by capillary action, taking some of the coloured substances with it
- different substances have different solubilities so will travel at different rates, causing the substances to spread apart
(those substances with higher solubility will travel further than the others)
what is the mobile phase?
the solvent in which the sample molecules can move e.g. water or ethanol
what is the stationary phase?
the stationary phase in paper chromatography (the actual chromatography paper)
what do more soluble substances do?
travel further up the paper- they spend more time in the mobile phase and are carried further up the paper than the less soluble components
how do you calculate Rf (retention factor) value?
Rf = distance moved by substance / distance moved by solvent
what are the units for Rf value?
it is a ratio and therefore has no units (+ will be less that 1)
what is a flame test?
a method of identifying a metal ion by the colour it produces in a roaring flame
describe the process of doing a flame test?
- dip a nichrome wire in HCl and burn it in a bunsen burner (washing)
- repeat the washing process until no color comes from the wire
- dip the nichrome wire in the substance being tested
- hold it in the flame and observe the color
what colors do the following metal ions produce in a flame test; sodium, calcium, lithium, copper, potassium?
sodium- yellow
calcium- orange/red
lithium- crimson red
copper- blue/green
potassium- lilac
what is another method of identifying metal ions?
metal hydroxide test- NaOH + ion forms a colored precipitate
what color precipitates do the following ions produce; iron (II), iron (III), copper, aluminium, magnesium
iron (II)- green
iron (III)- reddish brown
copper- blue
aluminium- white
magnesium- white
how would you distinguish between Al and Mg ions?
aluminium precipitate redissolves in excess NaOH, magnesium does not
what is the test for carbonate ions?
add dilute acid- if it fizzes, if test is positive
the gas (CO2) will turn the limewater cloudy.
what is the test for sulfate ions?
add dilute nitric acid and dilute barium nitrate - a white precipitate forms if sulfate ions are present
why should you not use hydrochloric acid in the sulfate test?
sulfate test is performed before halide test- adding HCl puts chloride ions in the solution which would mess with the results in the halide test
what is the test for halide ions?
add nitric acid and silver nitrate solution
what are the positive results for halide test?
chloride- white precipitate
bromide- cream precipitate
iodide- yellow precipitate
what are instrumental methods of testing?
use of machines to detect chemicals- eg flame emission spectroscopy
what are the advantages of instrumental methods?
accurate, sensitive, rapid
what are disadvantages of instrumental methods?
usually expensive, require training, must compare results to known samples
what are advantages of flame emission spectroscopy?
can spot multiple ions, can find ion concentration, can detect ions in very small samples
