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Chemistry > M8 Applying Chemical Ideas > Flashcards

M8 Applying Chemical Ideas Flashcards

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1
Q

Eutrophication

A

the enrichment of waterways by addition of nutrients (phosphates, nitrates) by fertilisers in run-off. Causes algal blooms then lack of photosynthesis in underwater plants, therefore lack of oxygen.

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2
Q

Why is it important to monitor the environment?

A

So that pollution can be controlled by knowing the source and the pollutant type.

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3
Q

Sources of pollution

A

Chemical spills (cause death of organisms, contamination of soil, waterways), Fertilisers (run-off into waterways, causes eutrophication).

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4
Q

Copper cation Cu2+ tests

A
  • blue precipitate with OH-, which dissolves in NH3 to form a deep blue solution.
  • Blue-green flame colour
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5
Q

Iron (II) cation Fe2+ tests

A
  • precipitate with OH- green or white, which may turn brown.
  • decolourises acidified dilute potassium permanganate solution.
  • Gold colour flame, may also be bright blue or green turning to orange-brown.
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6
Q

Iron (III) cation Fe3+ tests

A
  • orange-brown precipitate with OH-
  • no precipitate Cl-
  • deep red solution with thiocyanate (SCN-)
  • orange-brown flame colour
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7
Q

Barium cation Ba2+ tests

A
  • no precipitate with OH- and F-
  • white precipitate with SO4(2-)
  • pale green flame colour
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8
Q

Silver (I) cation Ag+ tests

A
  • orange-brown precipitate with OH-

- white precipitate with Cl-

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9
Q

Lead (II) cation Pb2+ tests

A
  • white precipitate with OH-, which dissolves with excess OH-.
  • yellow precipitate with I-
  • light blue-grey flame colour
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10
Q

Calcium cation Ca2+ tests

A
  • White precipitate with OH- (if not too dilute), F- and SO4(2-)
  • brick red flame colour
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11
Q

Magnesium cation Mg2+ tests

A
  • white precipitate with OH-

- No precipitate with SO4(2-)

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12
Q

Carbonate anion CO3(2-) tests

A
  • Reaction with acid (HNO3), produce CO2, lime water turning cloudy/bubbles
  • pH between 8 and 10, turns red litmus blue
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13
Q

Hydroxide anion OH- tests

A
  • pH > 7, turns red litmus blue

- Addition of NH4+ followed by gently heating will produce ammonia gas

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14
Q

Chloride anion Cl- tests

A

Addition of AgNO3 to an acidified sample produces a white precipitate, which dissolves in dilute ammonia solution and darkens in sunlight

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15
Q

Bromide anion Br- tests

A

Addition of AGNO3 to an acidified sample produces a pale cream precipitate that dissolves in concentrated ammonia solution, solution darkens slowly in sunlight

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16
Q

Iodide anion I- tests

A
  • Addition of AgNO3 to an acidified sample produces a pale yellow precipitate that does not dissolve in ammonia solution, a solution not affected by sunlight
  • Addition of Pb(NO3)2 produces a yellow precipitate
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17
Q

Sulfate anion SO4(2-) tests

A
  • Addition of Ba(NO3)2 to an acidified sample of the solution produces a thick white precipitate
  • Acidification and addition of Pb(NO3)2 produces a white precipitate
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18
Q

Phosphate anion PO4(2-) tests

A
  • Addition of ammonia followed by Ba(NO3)2 produces a white precipitate
  • Addition of Mg2+ in an ammonia/ammonium nitrate buffer produces a white precipitate, Mg(NH4)PO4
  • Acidification with HNO3 followed by addition of ammonium molybdate solution ((NH4)2MoO4) produces a yellow precipitate: warming the mixture for a few minutes may be necessary
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19
Q

Acetate ion CH3COO- tests

A
  • Does not precipitate with any cations except concentrated Ag+
  • An aqueous solution may have a vinegar smell
  • Addition of neutral FeCl3 produces a reddish brown solution; filter, add dilute HCl and colour disappears.
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20
Q

Naturally occurring substances as pollutants

A
    1. If their concentrations exceed levels agreed to in regulations.
    1. If they are not in the right area. E.g. Ozone is important in the upper atmosphere but is a pollutant at ground level.
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21
Q

Atomic Absorption Spectroscopy (AAS)

A

measures small quantities (trace concentrations) of elements. Used to measure the concentration of specific metals in a chemical sample. The amount of light absorbed by the atoms in a sample is dependent on how many atoms there are. The type or wavelength of light absorbed by the atoms in a sample is dependent on what type of atoms are present.

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22
Q

Limitations of AAS

A
  1. Only works for metals (cathode only works if the element can conduct electricity).
  2. Must choose metal before starting (must use a lamp that emits the right wavelength of light - match element in sample).
  3. Can only detect one element at a time.
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23
Q

Absorption and concentration relationship

A

How much light a sample absorbs is directly proportional (linear increase) to the concentration of atoms.

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24
Q

Calibration curves

A

used to find the concentration of atoms from the absorbance reading. Concentration in ppm (parts per million - equivalent to mg/L: milligrams per litre).

25
Q

Applications of AAS

A

Used to monitor pollutants in air, water and soil. Monitor toxic heavy materials (e.g. mercury) in food and water.

26
Q

Gravimetric analysis

A

a technique that allows us to find out the composition of a mixture by separating out the components and weighing them.

27
Q

Precipitation titration

A

a form of volumetric analysis in which the formation of an insoluble coloured complex is used to indicate the end point of the titration. End point is when the indicator changes colour (e.g. potassium dichromate K2CrO7).

28
Q

Colourimetry

A

a method of identifying a coloured substance or determining its concentration in solution based on its ability to absorb parts of the visible spectrum.

29
Q

Colourimetry advantages

A

simple, low cost, can detect small colour differences impossible for the human eye to see, and you do not have to isolate the substance from the mixture to measure its concentration. Organic, inorganic substances.

30
Q

Calibration curve

A

absorbance vs wavelength

31
Q

Beer-Lambert Law

A

absorbance is directly proportional to concentration. A = (sigma)Lc. A is absorbance, (sigma) is molar absorptivity, L is the length of the cuvette, c is concentration.

32
Q

UV-Visible Spectrophotometry

A

can accurately measure very low concentrations of chemicals. Looks at absorption spectra. Visible range: 380-780 nanometers. UV range: 190-380 nanometers.

33
Q

Bromine water test

A

determining difference between alkanes and alkenes. Bromine water (brown/orange) decolourises when added to an alkene but does not react with alkanes when in absence of UV light.

34
Q

The Lucas test

A

determining difference between primary, secondary and tertiary alcohols. Lucas reagent: mixture of concentrated hydrochloric acid and anhydrous zinc chloride catalyst. Alcohol needs to be fairly soluble in aqueous solution. Tertiary alcohols react. Secondary react very slowly. Primary do not react.

35
Q

Test for carboxylic acid

A

Add carbonate. Acid + carbonate → Salt + Water + CO2. Bubble CO2 through limewater, turns cloudy. Or test with blue litmus paper: acidic turns red. To ensure acid is carboxylic acid react with alcohol (esterification).

36
Q

Oxidation test for alcohols

A

Oxidation of primary, secondary alcohols with Cr2O72- (orange to green) or KMnO42- (purple to clear). Tertiary do not oxidise. Reduction of oxidising agent causes colour change.

37
Q

Test for alcohols

A

After oxidised, react with Benedicts / Fehling’s solution (contains copper (II)). Primary (aldehydes) blue to red precipitate. Secondary (ketones) no colour change, stays blue. Tertiary do not react.

38
Q

Alkoxide

A

conjugate base of an alcohol.

39
Q

Redox reaction

A

Metal + Alcohol → Metal Alkoxide + Hydrogen gas.

40
Q

Sodium test

A

tests for presence of hydroxides (cannot be aqueous form as sodium violently reacts with water; therefore liquid form). 2C2H5OH (ox agent, reduced, gains electrons) + 2Na (red agent, oxidised, loses electrons) → 2NaC2H5O + H2

41
Q

Mass Spectrograph

A

y-axis: relative abundance. x-axis: molar mass.

42
Q

Mass Spectrometer

A

vaporised sample, electron gun ionises molecules, accelerated through electric field, magnetic field (electromagnet), lighter and higher charged particles deflected more, detector.

43
Q

Base peak

A

100 relative abundance (highest abundance)

44
Q

Parent molecular ion

A

gives the molar mass of the original compound

45
Q

mass/charge ratio

A

If the mass/charge ratio is too small, they are deflated too much and don’t reach the detector, same if too big. Free radicals (e.g. H+) are not detected.
Uncharged molecules are not detected by mass spec.

46
Q

Nuclear Magnetic Resonance (NMR)

A

commonly used technique for organic compound structure determination. H NMR and C NMR.

47
Q

H NMR

A

applying an external magnetic field causes the nuclei spin to flip. The environment of the proton/hydrogen in the molecule affects where the signal is seen on the resultant spectrum. More electronegative (e.g. next to O), more to the right.

48
Q

Anti-parallel spin state

A

high level of energy, unstable. North of magnetic field is in opposite direction to north or the nucleus.

49
Q

Identical carbon environments

A

Identical carbon environments (in symmetrical molecules) will be the same peak.

50
Q

nucleus magnetic spin

A

e.g. C-13 can generate its own magnetic field (spin) due to an odd number of protons and/or neutrons.

51
Q

Electron shielding

A

Electrons from neighbouring elements can shield the carbon nuclei from an external magnetic field (changes the energy required to flip a nucleus).

52
Q

NMR graph

A

x-axis: chemical shift (ppm). 0 ppm is far right (up field), created by nuclei with high electron shielding. Downfield (left): lower electron shielding, absorb and emit lower frequency radio waves. y-axis: absorbance.
Carbons bonded to high electronegative atoms (e.g. 0) have low electron shielding as the O atom draws electrons closer to it, therefore will be to the left.

53
Q

Tetramethylsilane

A

used as a reference in NMR. Molecule with 0 ppm, highest electron shielding possible. Don’t count any 0 peak as a peak.

54
Q

Infrared spectroscopy

A

looks at how infrared radiation interacts with organic molecules. Atoms with higher masses will absorb lower frequency radiation. The same bonds in different places on a molecule will absorb different frequencies. Y-axis: percentage transmittance. X-axis: decreasing wavenumber (cm-1: inverse of wavelength) Identifies functional groups. IR causes bonds to vibrate.

55
Q

Spectra fingerprint region

A

1500-500 cm-1. Is unique to a compound.

56
Q

Yield

A

the amount of product, usually by mass, formed in a chemical reaction.

57
Q

Theoretical yield

A

amount of product that ‘should’ form if all reactants are used.

58
Q

Haber process (ammonia)

A

high temperature maximises rate, low temperature maximises yield.

Chemistry (4 decks)

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