T8 chemical analysis Flashcards
what is a pure substance
single element or compound, not mixed with any other substance
what is a formulation and how is it made
give examples
- mixture of compounds in measured quantities that has been designed as a useful product
- formulations include fuels, cleaning agents, alloys, medicines, fertilisers
e. g. alloys are mixtures of metals, harder than pure metals so have a particular purpose
describe paper chromatography
- start line is drawn near the bottom of the paper. Mixture is spotted on the line
- beaker is filled with small amount of solvent
- paper is hung on a rod and placed in a beaker
- solvent travels up the paper, separating the components
- before solvent level reaches the end, paper is taken out and the finish line is marked, paper is dried
- procedure works when different compounds have different affinities for the solvent/paper. Stronger attraction for the paper - travels slowly with the solvent
- paper is called the stationary phase - doesn’t move, solvent is the mobile phase
how is Rf calculated
distance moved by the spot / distance moved by solvent
describe the tests for hydrogen, oxygen, carbon dioxide and chlorine
H - pop with burning split over gas
O - glowing split relights
D - turns limewater (Ca(OH)2) milky
C - bleaches damp litmus paper and makes it white
describe the flame test results
lithium compounds - crimson red flame sodium compounds - yellow flame potassium compounds - lilac flame calcium compounds - orange red flame copper compounds - green flame
describe the test for carbonate anions
add dilute acid e.g. HCl
fizzing observed as CO2 released
describe sulfate tests
add a solution containing Ba2+ cations
white precipitate pf BaSO4 forms
describe silver nitrate tests
add a solution of AgNO3 (acidified with HNO3)
chlorines - white precipitate, silver chloride
bromides - cream precipitate, silver bromide
iodides - yellow precipitate, silver iodide
what are instrumental methods
accurate, sensitive and rapid methods which are useful when the amount of sample is very small
describe the flame emission spectroscopy
a) instrumental method used for identifying metal ions in solution or measuring their concentration
b) Spectroscope measures the exact wavelength of the light emitted by a metal ion
c) That allows for definite identification - sometimes colours are difficult to
distinguish.
d) Concentrations are found by measuring the intensity of light emitted. The more intense light, the greater the concentration of the metal ion in a solution.
e) From the intensity vs concentration graph, you can read off a relevant
concentration value at a given intensity.
what are cations and anions
c - positive ions
a - negative ions
describe the sodium hydroxide test results
copper (II) forms a blue precipitate
iron (II) forms a dirty green precipitate
iron (III) forms a brown precipitate
Al3+, Ca2+, Mg2+ forms white precipitate but only Al(OH)3 dissolves in excess NaOH to form a colourless solution
in paper chromatography experiment, a compound A was found to have an Rf value of 0.85 - what does it tell you about the compound
has a higher affinity for the solvent than for the paper