Ch12 Chemical analysis Flashcards
pure susbtance
single element or compound not mixed with any other substance
melt and boil at specific temperatures(fixed points)
melting and boiling point data
used to identify a pure substance
Formulation
a mixture that has been designed to produce a useful product with required properties
examples of formulations
fuels, cleaning agents, paints, medicines, alloys, pesticides, fertilisers and
foods
Test for hydrogen
uses a burning splint held at the open end of a test tube of the gas
the hydrogen burns rapidly with a pop sound
Test for oxygen
glowing splint inserted into a test tub of the gas
the splint relights in oxygen
Test for carbon dioxide
uses an aqueous solution of calcium hydroxide(lime water)
when CO2 is shaken with or bubbled through limewater turns milky(cloudy)
Test for chorine
Damp blue litmus paper is put into the chlorine gas
The litmus paper is bleached and turns white
Lithium flame test
crimson
Sodium flame test
yellow
Potassium flame test
lilac
Calcium flame test
orange-red
Copper flame test
green
Flame test method
- A nichrome wire loop must be dipped into concentrated hydrochloric acid and then heated to clean it
- re-dipped into the acid before dipping it into the metal compound
- Hold the loop in the flame of a Bunsen burner
- Use the colour of them flame to identify the metal ion in the compound
- If the sample contains a mixture of metal ions, some flame colours can be masked
copper with sodium hydroxide
blue precipitate is formed
iron(II) with sodium hydroxide
green precipitate is formed
Fe2+(aq) + 2OH-(aq) –> Fe(OH)2(s)
iron(III) with sodium hydroxide
brown precipitate is formed
calcium with sodium hydroxide
white precipitate is formed
magnesium with sodium hydroxide
white precipitate is formed
aluminium with sodium hydroxide
white precipitate is formed
aluminium hydroxide precipitate dissolves in excess sodium hydroxide solution
Al3+(aq) + 3OH-(aq) –> Al(OH)3(s)
test for carbonate ions
add dilute hydrochloric acid
bubbles are produced -carbon dioxide
CO3 2- + 2H+ –> CO2 + H2O
can be tested with limewater
Test for halide ions
Add dilute nitric acid to the unknown compound
Then add silver nitrate solution
Positive for halide ions if a precipitate forms
iodide ions with halide test
yellow precipitate
bromide ions with halide test
cream precipitate
chloride ions with halide test
white precipitate
test for sulfate ions
add dilute hydrochloric acid to unknown compound to remove carbonate ions
then add barium chloride solution
Positive for sulphate ions if a white precipitate forms(barium sulphate)
Ba2+(aq) + SO42-(aq) –> BaSO4(s)
Advantages for instrumental methods
highly accurate and sensitive
quicker
enable very small samples to be analysed
Disadvantages for instrumental methods
very expensive
takes special training to use
gives results that can often be interpreted only by comparison with data from known substances
Instrumental methods
used to detect and identify elements and compounds
Flame emission spectroscopy
instrumental
method used to analyse what metal ions are in solutions and the concentration
Method of flame emission spectroscopy
- solution is heated in a flame
- energy provided excites electrons in the metal ions, causing them to jump up energy levels
- when they fall back into low energy levels, energy is released as light energy, outputting a line spectrum
- line spectrum is used to identify the metal ion by comparing it on a computer database
- spectrometer can measure the intensity(absorbance) and wavelength of light to measure the concentration of the metal ions
Mobile phase in chromatography
the chosen solvent moves through the stationary phase, carrying the components of the mixture under investigation
Stationary phase in chromatography
the paper
Rf value in chromatography
retention factor
distance moved by substance/ distance moved by solvent
helps identify the compounds
