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Chemistry > Elements From The Sea > Flashcards

Elements From The Sea Flashcards

1
Q

What is the equation for percentage atom economy?

A

Atom economy = (molecular mass of desired products/sum of all products) x 100

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2
Q

Is the anode positive or negative?

A

Positive

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3
Q

Is the cathode positive or negative

A

Negative

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4
Q

What characteristic should electrodes have?

A

Inert so they don’t react

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5
Q

What are rules at the cathode for aqueous solutions

A

If the metal is less reactive than hydrogen it will be formed

If it is more reactive (group 1 and 2 and aluminium) hydrogen gas is formed

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6
Q

What rule for the anode for an aqueous solution

A

If it doesn’t contain a halide, or is a dilute solution containing a halide, oxygen will be formed

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7
Q

How can halogens be extracted?

A

Electrolyse concentrated solution containing halogens

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8
Q

In electrolysis where are halogens released

Is it oxidation or reduction

A

Anode

Oxidation

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9
Q

What is brine

A

A solution of water with a high concentration of salts - mainly sodium chloride but also some bromine and iodine salts

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10
Q

Why do you have to use concentrated halide solutions for electrolysis?

A

Because in dilute solutions they’re not discharged

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11
Q

How are bromine and iodine produced from brine?

A

Bubbling chlorine gas displaced it

it is then collected condensed and purified

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12
Q

What is an electrolyte?

A

liquid that contains free ions so can conduct electricity in electrolysis

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13
Q

What electrodes are used for aqueous solutions? why?

A

Platinum or graphite because they’re inert

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14
Q

How do you do electrolysis of an aqueous solution?

A
  • Connect the electrode at the anode to the positive pole and the electrode at the cathode to the negative pole
  • Put electrodes in beaker with the electrolyte, making sure electrodes aren’t touching
  • turn on power supply
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15
Q

What will the half equation at the anode show?

A

negative ions losing electrons to form atoms

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16
Q

What will the half equation at the cathode show?

A

positive ions gaining electrons to form atoms

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17
Q

What does a molten ionic compound break into in electrolysis?

A

Its elements

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18
Q

Where and how does brine naturally occur?

A

salt lakes or as sea water

by rock salt dissolving in water

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19
Q

What happens at the cathode during the electrolysis of brine?

A

Hydrogen ions accept electrons to become one hydrogen gas molecule

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20
Q

What happens at the anode during the electrolysis of brine

A

Chlorine gas is formed

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21
Q

What is an oxidation state?

A

How many electrons it has donated or accepted to form an ion or bond

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22
Q

What electron state do O2 and Ag ?

A

0

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23
Q

What is the oxidation state for an ion of 1 atom (Na+)?

A

The same as its charge (Na+ would be +1)

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24
Q

What is the overall oxidation state for a molecular ion?

A

The same as the overall charge

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25
Q

What is combined oxygens usual oxidation state?

A

-2

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26
Q

What is the usual oxidation state of combined hydrogen?

A

+1

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27
Q

What is the overall oxidation state of a neutral compound?

A

0

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28
Q

What does it mean if an ion ends in -ate? (sulfate)

A

Made of oxygen and another element

sulfur and oxygen

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29
Q

What is (NO3)- called?

A

nitrate(V)

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30
Q

What is (SO4)2- called?

A

Sulfate(VI)

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31
Q

What is (CO3)2- called?

A

carbonate

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32
Q

What is (MnO4)- called?

A

Manganate(VII)

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33
Q

What is OH- called?

A

Hydroxide

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34
Q

What is (NH4)+ called?

A

Ammonium

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35
Q

What is (HCO3)- called?

A

hydrogencarbonate

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36
Q

What is (S)2- called?

A

Sulfide

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37
Q

What is (SO4)2- called?

A

Sulfate(VI)

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38
Q

What is (SO3)2- called?

A

Sulfate(VI)

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39
Q

What is oxidation?

A

loss of electrons

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40
Q

What is reduction?

A

gain of electrons

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41
Q

What happens to reducing agents?

A

They are oxidised and donate electrons

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42
Q

What happens to oxidising agents?

A

They are reduced and accept electrons

43
Q

What are iodine-sodium thiosulphate titrations used for?

A

Finding the concentration of an oxidising agent

44
Q

How do you clean the burette for titration?

A

rinse it out with the solution going in it (eg. sodium thiosulphate)
- using water will leave traces which will dilute the solution

45
Q

What is the equation for concentration?

A

conc = moles/vol(dm^3)

46
Q

What do you add so you can see the end point easier in iodine-sodium thiosulphate titrations? When?

A

Starch solution - when the solution turns pale yellow

47
Q

What is the end point for an iodine - sodium thiosulphate titration?

A

Blue –> clear

clear when the iodine has reacted

48
Q

What is the end point?

A

the point where the alkali is exactly neutralised and the indicator changes colour

49
Q

What are halogens?

A

Group 7 elements

50
Q

What does fluorine look like at room temp?

A

pale yellow gas

51
Q

What does chlorine look like at room temp?

A

yellow-green gas

52
Q

What does bromine look like at room temp?

A

red-brown liquid

53
Q

What does iodine look like at room temp?

A

Shiny grey solid

54
Q

What is volatility?

A

Measure of how easy it is to vaporise something?

55
Q

What is the volatility trend of halogens? why?

A

Less volatile down the group

because the increase in size and relative atomic mass so stronger id-id bonds

56
Q

Why do halogens have higher solubility in hexane?

A

It is an organic solvent

Halogens are covalent and non polar

57
Q

What colour is chlorine in water?

A

virtually colourless

58
Q

What colour is chlorine in hexane?

A

virtually colourless

59
Q

What colour is bromine in water?

A

orange

60
Q

What colour is bromine in hexane?

A

red

61
Q

What colour is iodine in water?

A

Brown

62
Q

What colour is iodine in hexane?

A

violet

63
Q

What is the reactivity trend of halogens?

A

Less reactive down the group

64
Q

Are halogens reducing or oxidising agents?

A

oxidising agents - gain an electron

65
Q

Why are halogens less reactive down a group?

A

larger atoms have more electron shells so outer electrons are further from nucleus
outer electrons more shielded from positive nucleus
so weak attraction to electron needed to form an ion

66
Q

What can halogens do to less reactive halide ions in solution?

A

Displace it

67
Q

What is reduced and what is oxidised in a displacement reaction between halogens and halides?

A

the displaced halid is oxidised

the displacing halogen is reduced

68
Q

What can you see with a halogen-halide displacement reaction?

A

colour change

69
Q

How can you make a hydrogen halide?

A

Add a conc acid to a solid ionic halide

eg. conc phosphoric acid to sodium chloride

70
Q

What hydrogen halides can’t you make with conc sulfuric acid? why?

A

hydrogen bromide/iodide

iodine and bromine can reduce sulfuric acid and become bromine or iodine gas

71
Q

What is the trend in bond energy for hydrogen halides?

A

Decreases down the group

so HF would be more stable than HI when heated

72
Q

Why does bond energy decrease down the group for hydrogen halides?

A

Bigger atoms so bonding electrons are
further away and
shielded from the nucleus

73
Q

Why are hydrogen halides acids in water?

A

It dissociates into the halogen ion and proton

74
Q

Why do you get an ammonium halide from hydrogen halide and ammonia?

A

Ammonia is a base
It accepts proton to form an ammonium ion
which bonds with halide ion

75
Q

What equation shows sodium chloride reacting with sulfuric acid?

A

NaCl + H2SO4 –> HCl + NAHSO4

76
Q

Which hydrogen halide is most thermally stable? why?

A

HF
Smallest so
strongest attraction to bonding electrons

77
Q

What acid work for all hydrogen halides when trying to make hydrogen halides from ionic halides?

A

Phosphoric acid

78
Q

What is a test for halides?

A

Use silver nitrate solution - a precipitate of silver halide is formed

79
Q

What precipitate is formed when fluoride reacts with silver nitrate?

A

no precipitate

80
Q

What precipitate is formed when chloride reacts with silver nitrate?

A

white precipitate

81
Q

What precipitate is formed when bromide reacts with silver nitrate?

A

cream precipitate

82
Q

What precipitate is formed when iodide reacts with silver nitrate?

A

yellow precipitate

83
Q

What do you use to tell apart the precipitates formed, in the test with silver nitrates and halides?

A

Ammonia solution

84
Q

How does AgCl react with ammonia solution?

A

dissolves to colourless in dilute ammonia solution

85
Q

How does AgBr react with ammonia solution?

A

dissolves to colourless in conc ammonia solution

86
Q

How does AgI react with ammonia solution?

A

Does not dissolve so stays the same

87
Q

Why is chlorine dangerous?

A
  • toxic
  • corrosive
  • flammable
88
Q

What is the equation for percentage atom economy?

A

(molecular mass of desired product) / (sum of molecular mass of all products)

89
Q

Is better to have a high or low atom economy? why?

A

High atom economy

they produce less waste so they’re cheaper and more environmentally friendly

90
Q

What is dynamic equilibrium?

A

The forward reaction and backward reaction reaction are the same rate

91
Q

What system does dynamic equilibrium need to be in?

A

A closed system

92
Q

Will there be more reactants or products when equilibrium is to the left?

A

more reactants

93
Q

Will there be more reactants or products when equilibrium is to the right?

A

more products

94
Q

What is Kc?

A

The equilibrium constant

95
Q

What is the Kc equation?

A

[PRODUCTS]/[REACTANTS]
A+ B –> C + 2D
[C] [D]^2 / [A] [B]

96
Q

What does it mean if Kc is more than 1?

A

equilibrium lies to the right

97
Q

What does it mean if Kc is less than 1?

A

Equilibrium lies to the left

98
Q

What does it mean if Kc is 1?

A

Equilibrium is in the middle (amount of reactants and products are equal)

99
Q

How does Kc stay constant?

A

the position of equilibrium shifts to keep it constant

100
Q

What does increasing pressure do to equilibrium?

A

Equilibrium shifts to side with fewer gas molecules

101
Q

What does decreasing pressure do to equilibrium?

A

Equilibrium shifts to side with more gas molecules

102
Q

What does increasing temperature do to equilibrium?

A

Equilibrium shifts to endothermic side

103
Q

What does decreasing temperature do to equilibrium?

A

Equilibrium shifts to exothermic side

Chemistry (8 decks)

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