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chemistry > 8 Chemical analysis > Flashcards

8 Chemical analysis Flashcards

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1
Q

what is a pure substance

A
  • a single element or compound, not mixed with any other
    substance
  • have specific melting and boiling points
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2
Q

what is a formulation

A
  • a mixture that has been designed as a useful product
  • made by mixing components in carefully measured quantaties
  • eg. fuels, cleaning agents, paints, medicines, alloys, fertilisers, foods
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3
Q

how can you check an unknown substance is pure

A
  • measure its melting or boiling point and comapre it with the melting/boiling point of the pure substance
  • the closer the measure value to the actual melting/boiling point the purer the sample
  • impurities in a sample will lower the melting point and increase the melting range
  • impurities will increase boiling point
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4
Q

what is chromotography

A
  • an anyltical method used to seperate substances in a mixture
  • can be used to identify substances
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5
Q

what are the 2 phases in chromatography

A
  • mobile phase - where molecules can move, always a liquid or gas
  • stationary phase - where the molecules can’t move, can be solid or really thick liquid
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6
Q

the time spent in each phase depends on what?

A
  • how soluble they are in the solvent
  • how attracted they are to the paper
    (molecules with a higher solubility in solvent and less attracted will travel further)
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7
Q

chromotography practical

A
  1. Use a ruler to draw a horizontal pencil line 2 cm from the bottom short edge of the chromatography paper- origin line
  2. add a spot of ink to the line and place the sheet in a beaker of solvent eg. water
  3. add the piece of paper into the water with only the bottom submerdeged eg. 1cm
  4. clip the top to a wooden spill resting on the top of the beaker
  5. put a lid on top to stop the solvent evaporating
  6. the solvent seeps up the paper carrying the ink with it
  7. each dye in the ink will move up the paper at different rate forming a spot
  8. if any ink is insoluable it will stay on the baseline
  9. when the solvent has nearly reached the top of the paper take it out and dry it
  10. the end result is a chromotogram
    analysis(8):
  11. measure the distance traveled by the solvent
  12. measure the distance in mm between the centre of the spots of dyes and the base line
  13. calculate the Rf = distance travelled by substance/distance travelled by solvent
  14. compare the ratios of the different dyes
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8
Q

why are different solvents sometimes used

A
  • depends on solubility
  • some compunds dissolve well in water but sometimes other solvents like ethanol are used
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9
Q

what can chromotography be used for

A

to find if a substance is present in a mixture:
- run a pure sample of the substance alongside the unknown mixture
- if the Rf values to the refrence and one of the spots match the mixture, the substance may be present

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10
Q

Rf=

A

distance traveled by substance/distance traveled by solvent

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11
Q

gas tests

A

hydrogen - squeaky pop with a burning splint over gas
oxygen - glowing splint relights
Carbon dioxide - turns lime water cloudy
Chlorine - bleaches damp litmus paper white

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12
Q

how can you detect Carbonates (anion)

A
  • put a sample of unknown solution and add a couple drops of dilute acid
  • connect the test tube to a test tube of limewater, if carbonates present, carbon dioxide will be released that will turn the limewater cloudy when it bubbles
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13
Q

test for sulfates

A
  • use a dropping pippette to add a couple of drops of dilute HCl acid
  • then add a couple drops of BaCl barium chloride
  • if sulfate ions present a white precipiatate of barium sulfate will form

Ba2+ (aq) + SO42-(aq) —> BaSO4 (s)

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14
Q

test for halides

A
  • add a couple drops of dilute nitric acid (HNO3)
  • add a drops of silver nitrate solution AgNO3 to the unknown soluution
  • Chloride gives a white precipitate of silver chlorise Ag+ + Cl- —> AgCl
  • Bromide gives a cream precipitate of silver bromide Ag+ + Br—> AgBr
  • An iodide gives yellow precipitate of silver iodide Ag+ + I —> AgI
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15
Q

flame tests for cations results

A
  • Lithium burn a crimson flame - crimson LIpstick , lithium
  • Sodium burn a yellow flame Sodium - Sun - yellow
  • Pottasium burn a lilac flame - Potassium Purple - lilac
  • Calcium burn an orange-red flame - 2c’s so 2 colours
  • Copper burns a green flame
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16
Q

how to do a flame test

A
  • clean a platinum wire loop by dipping it in some dilute HCl and hold it in a blue flame from a bunsen burner until it bruns with no colour - tp get rid of ny impurities
  • dip the loop into the sample you want to test and put it back in the flame
  • record the colour of the flame
  • only works if sample contains a single metal ion
17
Q

how to do a precipitate test

A
  • add a few drops of sodium hydroxide to a solution of unknown compound
  • record the colour and find which metal is present
18
Q

precipitate test for cations NaOH results

A

calcium - white = Ca2+ + 2OH- –> Ca(OH)2
copper(II) - blue= Cu2+ + 2OH- —> Cu(OH)2
Iron(II) - green = Fe2+ + 2OH- —> Fe(OH)2
Iron(III) - brown = Fe3+ + 3OH- —> Fe(OH)3
Aluminium - white at first the redisolves excess NaOH to produce a colourless solution = Al3+ + 3OH- —> Cu(OH)3
Magnesium - White = Mg2+ + 2OH- —> Mg(OH)2

19
Q

describe flame emission spectroscopy

A
  • a sample is placed in a flame
  • as ions heat up their electrons become exited, when drop back to their orginal energy levels they transfer energy as light
  • the light passes through a spectroscope which detects different wavelengths of light to produce a line spectrum
  • different ions hit different wavelengths of light so each ion has a different pattern of wavelengths
  • intensity of the spectrum indicates the concentration of that ion in solution
  • means line spectrums can be used to identify ions in a solution and calculate their concentrations
  • can also be used to identify ions in mixtures - compare spectrums for different ions to the spectrum of a mixture

chemistry (11 decks)

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