C8: Chemical analysis Flashcards
What is chemical analysis?
The process of establishing what chemicals are present in a substance
What is a pure substance?
- a pure substance is a single element or compound , not mixed with any other substance
What is a formulation and how is it made? Give an example
- a mixture of compounds in measured quantities that has been designed as a useful product
- formulations include fuels, cleaning agents, paints , medicines, alloys
What is chromatography?
A process to separate the constituents of a mixture
In paper chromatography, what is
the stationary phase and what is
the mobile phase
Paper is stationary, solvent (usually water or ethanol) is mobile
How can chromatography show
the difference between pure and
impure substances?
Pure ones will not separate into a number of spots
How is the Rf value calculated?
Rf = distance moved by spot/distance moved by solvent
Describe the tests for hydrogen, oxygen, carbon dioxide and chlorine.
hydrogen: pop with burning splint over gas
oxygen: glowing splint relights
carbon dioxide: turns limewater milky
chlorine: bleaches damp litmus paper and makes it white
Describe the 5 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
In chromatography, why must the
substances be placed on a pencil
line?
Pencil will not dissolve in the solvent
In chromatography why must the
solvent height be lower than the
pencil line?
So that the substances do not dissolve into the solvent off the paper
Describe the sodium hydroxide test results for
- aluminium
- calcium
- magnesium
they all form white precipitates of ( metal) hydroxide
How would you
differentiate between
aluminium ions in one
solution , calcium ions in
a second and
magnesium ions in a
third solution
● Only the aluminium hydroxide precipitate will
redissolve in excess sodium hydroxide
● The solutions containing calcium and
magnesium can be distinguished using a flame
test. The solution containing calcium will
produce an orange-red flame colour
Describe the sodium hydroxide results for:
- copper (||) ions
- iron (||) ions
- iron (|||)
copper - blue precipitate of copper hydroxide
iron (||) - Green precipitate of iron (II) hydroxide
iron (|||) - Brown precipitate of iron (III) hydroxide
Write the balanced and ionic
equation for the reaction
between copper (II)
sulphate and sodium
hydroxide
balanced: CuSO₄ (aq) + 2NaOH (aq) ➝ Cu(OH)₂ (s) + Na₂SO₄ (aq)
ionic: Cu₂₊ (aq)+ 2OH- (aq) ➝ Cu(OH)₂ (s)
Write the balanced and ionic equation for the reaction between magnesium sulphate and sodium hydroxide
balanced : MgSO₄ (aq) + 2NaOH (aq) ➝ Mg(OH)₂
(s) + Na₂SO₄ (aq)
ionic: Mg₂₊ (aq) + 2OH- (aq) ➝ Mg(OH)₂ (s)
Write the balanced and ionic equation for the reaction between iron (|||) chloride and sodium hydroxide?
balanced: FeCl₃ (aq) + 3NaOH (aq) ➝ Fe(OH)₃ (s) + 3NaCl (aq)
ionic: Fe₃₊ (aq) + 3OH-(aq) ➝ Fe(OH)₃ (s)
- Describe how to
test for the presence of
carbonate ions.
Add dilute acid to sample
Give 2 observations
seen if carbonate ions
are present
● Effervescence
● Bubble the gas into a test tube containing limewater.
- The limewater will turn cloudy
showing the presence of carbon dioxide
Describe how to test for the presence of
sulphate ions. Give the observation seen for a
positive result
● Add dilute hydrochloric acid to the sample to
remove any carbonates
● Add barium chloride to the sample
● White precipitate of barium sulphate formed if the sample contained sulphates
Describe how to test for the presence of
halide ions. Give the observation seen for the
presence of chloride,bromide and iodide ions
● Add dilute nitric acid to remove any carbonates
● Add silver nitrate
● Chloride ions: white precipitate of silver
chloride forms
● Bromide ions: cream precipitate of silver
bromide forms
● Iodide ions: yellow precipitate of silver iodide
forms
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?
cations: positive ions
anions: negative ions
