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AQA Chemistry > Chemical Analysis > Flashcards

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

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2
Q

how can we find out if a substance is pure using its mp/bp?

A

Pure substances melt and boil at a specific temp

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3
Q

what is a formulation?

A

a mixture that has been designed as a useful product eg. paint, fuel, medicine, alloys, fertilisers

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4
Q

how are formulations made?

A

mixing the components in carefully measured quantities to ensure that the product has the required properties

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5
Q

what phases does chromatography have?

A
  • mobile phase=where molecules can move eg. a liquid or gas
  • stationary phase=where molecules can’t move eg. a solid or really thick liquid
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6
Q

what are the phases in paper chromatography?

A
  • stationary phase=chromatography (filter) paper
  • mobile phase=solvent eg. water/ethanol
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7
Q

what is the time molecules spend in each phase affected by?

A
  • how soluble they are
  • how attracted they are to the paper
  • high solubility+less attracted to paper=more time in mobile phase=further up the paper
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8
Q

what is an Rf value?

A

ratio between distance travelled by solute and distance travelled by solvent

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9
Q

Rf value equation

A

distance moved by substance/distance moved by solvent

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10
Q

how can we identify pure substances with chromatography?

A
  • pure compounds will produce a single spot in all solvents
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11
Q

what are Rf values dependent on?

A

solvent
- changing solvent=different Rf values

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12
Q

required practical: chromatography

A
  • like normal chromatography but Rf value calculated
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13
Q

test for hydrogen

A

squeaky pop test
- burning splint held at the open end of a test tube of the gas
- hydrogen burns rapidly with a pop sound

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14
Q

test for oxygen

A
  • glowing splint inserted into a test tube of the gas
  • splint relights in oxygen
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15
Q

test for CO2

A
  • aqueous solution of calcium
    hydroxide (lime water)
  • CO2 is shaken with or
    bubbled through limewater the limewater turns milky/cloudy
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16
Q

test for chlorine

A
  • damp litmus paper is
    put into chlorine gas
  • litmus paper is bleached and turns white (may turn red first because chlorine solution=acidic)
17
Q

flame tests

A
  • lithium=crimson flame
  • sodium=yellow flame
  • potassium=lilac flame
  • calcium=orange-red flame
  • copper=green flame
  • a sample containing a mixture of ions is used some flame colours can be masked
18
Q

metal hydroxide tests

A
  • calcium - white precipitate
  • magnesium - white
  • aluminium - white+dissolves in excess sodium hydroxide solution=colourless
  • iron (II) - green
  • iron (III) - brown
  • copper - blue
19
Q

equations for metal hydroxides

A
  • calcium
    Ca+2 + 2OH- –> Ca(OH)2 (s)
  • magnesium
    Mg+2 + 2OH- –> Mg(OH)2
  • aluminium
    Al+3 + 3OH- –> Al(OH)3
  • iron (II)
    Fe+2 + 2OH- –> Fe(OH)2
  • iron (III)
    Fe+3 + 3OH- –> Fe(OH)3
  • copper
    Cu+2 + 2OH- –>Cu(OH)2
20
Q

carbonates test

A
  • add a couple drops of dilute acid eg. HCl to your solution in a test tube
  • using a bung, connect test tube with solution with a test tube with limewater
  • if CO2 released, limewater=milky/cloudy
21
Q

halides test

A
  • add a couple drops of dilute nitric acid (HNO3)
  • add a couple drops of silver nitrate (AgNO3)
  • chlorine - white
  • bromine - cream
  • iodine - yellow
22
Q

sulfates test

A
  • use a dropping pipette, add a couple drops of dilute HCl+barium chloride (BaCl2) to a test tube with the solution you’re testing
  • barium sulfate will form if barium is present
  • Ba+2 + SO4 -2 –> BaSO4
23
Q

what are instrumental methods?

A
  • a way of detecting+identifying elements/compounds
24
Q

pros of instrumental methods

A
  • very sensitive - detect tiny amounts
  • very fast - can be automated
  • vary accurate
25
Q

flame emission spectroscopy

A
  • an instrumental
    method used to analyse metal ions in solutions
  • sample is put into a flame=electrons become excited
  • electrons drop back to original energy level=transfer energy as light
  • light given out is passed
    through a spectroscope=detects different wavelengths=produces line spectrum
  • combination of wavelengths emitted by ion depend on its charge+electron arrangement
  • different ions=different wavelengths=different line spectrum
  • intensity of spectrum=concentration

AQA Chemistry (10 decks)

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