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Chem C4-C6 > C4.2 - Identifying Products of Chemical Reactions > Flashcards

C4.2 - Identifying Products of Chemical Reactions Flashcards

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1
Q

How do you detect CO2 (and how does it work)?

A
  • Bubble the gas through limewater (calcium hydroxide solution)
  • if it turns cloudy, The gas is CO2
  • it works by…limewater + CO2 reacting to product a white precipitate
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2
Q

How do you detect chlorine (and why does it work)?

A
  • hover a dampened piece of blue litmus paper above the substance
  • if chlorine present, paper bleaches (turns red then white)
  • this works because….chlorine bleaches dyes
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3
Q

Why does the litmus paper have to be damp?

A
  • As when chlorine reacts with water it creates an acidic solution.
  • therefore, the water allows the litmus paper and chlorine to react
  • and so the paper becomes bleached
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4
Q

What must you do to make sure you are not harmed when smelling substances in a laboratory?

A
  • keep container a few cm away from nose + a cautious sniff

Make sure you do not breathe in a lot of substance

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5
Q

How do you detect for hydrogen?

A
  • place a lit splint (you can see a flame) near the mouth of test tube
  • it should ignite with a ‘squeaky pop’ sound
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6
Q

How do you detect for oxygen?

A
  • place a glowing splint (so almost gone), into mouth of test tube
  • flame should relight (becomes a roaring flame)
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7
Q

Describe why a flame test works (the science behind it)

A
  • when metal ions are heated, energy is transferred to electrons
    |
    \/
    Electrons move to higher electron shells (outwards) - now unstable
    |
    \/
    When electrons move back to normal energy shells, energy is transferred to surroundings as radiation (we see as light, or a flame)
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8
Q

Why do different metals produce different colours of light?

A

As they have different chemical properties or different placed electrons, so the electrons jump different lengths (different wavelength so different colour produced)

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9
Q

What kind of ions do flame tests work on?

A

Metal ions (or cations - positive ions)

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10
Q

How do you carry out a flame test?

A

1) clean nichrome wire loop (with handle), by dipping in HCl acid
2) then rinse it in distilled water
3) place into bunsen burner to see if the blue flame changes colour, if it does dip it in HCL acid again and rinse it
4) dip clean loop into test power/solution
5) place loop into blue flame on Bunsen burner
6) record flame colour

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11
Q

What colour is lithium’s flame?

A

Red

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12
Q

What colour is sodium’s flame?

A

Yellow

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13
Q

What colour is potassium’s flame?

A

Lilac

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14
Q

What colour is calcium’s flame?

A

Orange-red

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15
Q

What colour is copper’s flame?

A

Green-blue

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16
Q

What would the colour of iron (II) precipitate be?

A

Green

17
Q

What would the colour of iron (III) precipitate be?

A

Orange-brown

18
Q

What would the colour of copper (II) precipitate be?

A

Blue

19
Q

What would the colour of calcium precipitate be?

A

White

20
Q

What would the colour of zinc precipitate be?

A

White, if you add excess of sodium hydroxide then it becomes colourless

21
Q

How do you perform a hydroxide precipitate test?

A

1) Add a few drops of sodium hydroxide solution to the solution containing metal ions
2) record the colour of the precipitate

22
Q

Why do you use sodium hydroxide solutions in a precipitate test?

A

As group 1 hydroxides are soluble in water (most other metal hydroxides are insoluble).

23
Q

why must you clean the wire loop between each test?

A

to ensure the substance being tested is not contaminated with the previous test substance

(not confuse the flame colours)

24
Q

how do you detect sulfate ions?

A

1) add a few drops of dilute hydrochloric acid
2) add a few drops of barium chloride solution

  • a white precipitate should form
25
Q

what is the basis to detect sulfate ions?

A

barium ions and sulfate ions react to make white insoluble barium sulfate

26
Q

state one measure used in a sulfate test to ensure the accuracy

A
  • dilute HCl acid is added
  • to remove the carbonate ions
    (or else they can react to produce a white precipitate)
27
Q

how do you detect carbonate ions?

A

1) add any dilute acid to sample (usually HCl)

  • would react to release CO2 gas
  • to check if CO2 bubble through limewater
28
Q

what is the basis to detect carbonate ions?

A

H+ ions in acid react with CO3 (2-) ions in the carbonate, to make CO2 + H20

  • so the CO2 gas is an indicator that carbonate ions are present
29
Q

how do you detect halide ions?

A

1) add a few drops of dilute nitric acid
2) add a few drops of silver nitrate solution

  • a precipitate is formed if chloride/bromide/iodide ions are formed
30
Q

difference between chlorine and chloride?

A

chloride is the ion of chlorine

31
Q

why is dilute nitric acid added in halide tests?

A

H+ ions in acid react with CO3 (2-) ions in solution

  • to prevent carbonate ions reacting with silver nitrate (as they also produce a white precipitate)
32
Q

what are the 3 colours produced in a positive halide test?

and what is the corresponding element

A

white, cream, yellow

chloride, bromide, iodide

33
Q

what are the advantages of instrumental methods of analysis?

A
  • more sensitive (can analyse small amounts of substance)
  • higher accuracy (can be calibrated using internationally accepted standards)
  • greater speed (analyse quickly + run all the time)
34
Q

give 3 features of a gas chromatogram and what they mean

A

each peak = a substance present in mixture

area under peak = relative amounts of substance

retention time = time taken for substance to travel through the chromatography column (diff. for diff substances)

35
Q

what does a mass spectrometer do?

A
  • measure the masses of atoms and molecules

- analyse the relative amounts of different isotopes of an element + structure of molecules

36
Q

give 3 features of a mass spectrum

A
  • each peak represents a fragment of the molecule
  • peak on far right represents the molecular ion (entire molecule)
  • mass to charge ratio of molecular ion = to Mr of substance (relative formula mass)
  • on x axis
37
Q

How does mass spectrometry work?

A
  • sample molecules are ionised by the machine to form molecular ions
  • these may break up to form fragments, which the machine can separate and detect

Chem C4-C6 (19 decks)

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