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chemistry > elements of the sea > Flashcards

elements of the sea Flashcards

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1
Q

calculation for % atom economy

A

% atom economy = ( Mr desired products / Mr reactants) x 100

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2
Q

aqueous rules of electrolysis at the cathode

A

hydrogen gas formed unless less reactive metal (silver, gold, or copper) present

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3
Q

aqueous rules of electrolysis at the anode

A

oxygen gas formed unless halide ions present

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4
Q

molten rules of electrolysis at cathode

A

cations gain electrons to form atoms

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5
Q

molten rules of electrolysis at anode

A

anions lose electrons to form atoms

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6
Q

process of extraction of bromine from seawater

A

chlorine more reactive than bromine and iodine
Br and I displaced by Cl
When chlorine gas is bubbled through brine, the chlorine displaces the bromine as it is more reactive, forming bromine gas

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7
Q

process of extraction of chlorine from seawater

A

electrolysis of seawater which contains conc. NaCl
- formation of hydrogen at cathode (as Na more reactive than hydrogen)
- formation of chlorine gas at anode

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8
Q

electrolysis definition

A

the passing of an electrical current through an aqueous or molten substance, breaking it down

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9
Q

anode definition

A

the positive electrode in electrolysis

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10
Q

cathode definition

A

the negative electrode in electrolysis

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11
Q

electrolyte definition

A

the substance (molten or aqueous) being broken down in electrolysis

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12
Q

oxidation definition

A

loss of electrons

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13
Q

oxidising agent definition

A

substance that oxidises another substance, gaining electrons

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13
Q

reduction definition

A

gain of electrons

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14
Q

reducing agent definition

A

substance that reduces another substance, losing electrons

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15
Q

redox reaction definition

A

a reaction where oxidation and reduction occur

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16
Q

disproportionation definition

A

a reaction where one molecule is both oxidised and reduced

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17
Q

oxidation state rule halogens

A

-1
unless with more reactive halogen
or unless with O (except F)

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18
Q

oxidation state rule for group 1

A

+1

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19
Q

oxidation state rule for group 2

A

+2

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20
Q

oxidation state rule for oxygen

A

-2, unless with F or as a peroxide

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21
Q

oxidation state rule for hydrogen

A

+1

22
Q

oxidation state rule for atoms in elements

A

0

23
Q

relationship between oxidation state and oilrig

A

if oxidation state decreases, atom has been reduced
if oxidation state increases, atom has been oxidised

24
Q

purpose of iodine thiosulfate titrations

A

to find the concentration of an oxidising agent, e.g. iodate

25
Q

process of iodine thiosulfate titrations

A

a) oxidising iodine
1. measure 25cm3 oxidising agent using volumetric pipette
2. add to excess of acidic potassium iodide solution
b) finding number of moles of iodine produced
1. titrate above solution with soidum thiosulfate
2. when solution = pale yellow, add drops of starch solution, will turn it black
3. continue titration, complete when solution is colourless

26
Q

appearance of fluorine

A

gas at room temp
pale yellow colour

27
Q

appearance of chlorine

A

gas at room temp
greenish yellow

28
Q

appearance of bromine

A

liquid at room temp
reddish brown

29
Q

appearance of iodine

A

solid at room temp
grey-black colour

30
Q

general properties of halogens

A

highly reactive
non-metals
diatomic
not very soluble (covalent + non-polar)

31
Q

halogen trends

A

as you go down the group
- boiling and melting point increases
- volatility decreases (due to stronger id-id bonds)
- reactivity decreases

32
Q

reactivity of halogens

A
  • remove electrons from other elements to complete their outer shell (oxidising agents)
  • decrease going down the group due to valence electrons further from core so attraction weaker + more electron shielding
33
Q

aqueous chlorine colour

A

colourless

34
Q

aqueous bromine colour

A

orange

35
Q

aqueous iodine colour

A

brown

36
Q

halide ions + silver ions

A

chlorine - white precipitate
bromine - cream precipitate
iodine - yellow precipitate

37
Q

silver halides + ammonia

A

silver chloride - dissolves in dilute ammonia
silver bromide - dissolves in concentrated ammonia
silver iodide - insoluble in ammonia

38
Q

making hydrogen halides with sulfuric acid

A

hydrogen chloride - made by adding conc. sulfuric acid to solid ionic chloride
bromide + iodide - can’t be made this way as Br and I are strong enough reducing agents to reduce sulfuric acid
with bromine -> makes Br2 gas + sulfate salt + water + SO2
with iodine -> makes I2 gas + H2S + water

39
Q

hydrogen halides when heated

A

HF and HCl -> stable + won’t break
HBr -> will slightly dissociate
HI -> will fully dissociate

40
Q

hydrogen halides with water

A

HF -> doesn’t fully dissociate in water, making it a weak acid
HCl, HBr, HI -> fully dissociates in water, strong acid

41
Q

hydrogen halides with ammonia

A

forms ammonium halide
NH4X (aq)

42
Q

hydrogen halides with sulfuric acid

A

HF and HCl -> do not react with sulfuric acid
HBr -> Br2 + SO2 + H2O
HI -> I2 + H2S + H2O

43
Q

risks of chlorine

A

a toxic gas, corrosive, irritates the respiratory system, risk of fires (oxidising agent)

44
Q

transportation of chlorine

A

stored in cylinders
transported by road or rail, in pressurised tank containers
transported as a liquid (more liquid can be stored in a fixed volume than gas)
venting mechanism to stop pressure getting too high

45
Q

uses of chlorine

A

sterilising water
in bleach
removes stains

46
Q

criteria for dynamic equilibrium

A
  • concentrations of the reactants and products stay constant
  • the forward and reverse reactions are both occurring
  • the rate of the forward reaction equals the rate of the reverse reaction
47
Q

equilibrium constant

A

Kc
described position of reaction at equilibrium
temperature dependent

48
Q

if Kc is greater than 1

A

there is a greater concentration of products over reactants at equilibrium

49
Q

if Kc is less than 1

A

there is a greater concentration of reactants over products at equilibrium

50
Q

Kc expression

A

aA + bB <=> cC dD

Kc = ([C]^c [D]^d) / ([A]^a [B]^b

Kc = [products] / [reactants]

51
Q

calculating Kc with correct units method

A
  1. write Kc expression
  2. sub in values + solve
  3. for units - sub in moldom-3 into Kc expression and solve by cancelling units
52
Q

effect of changing pressure on equilibrium

A

Increasing pressure shifts the equilibrium to the side with the fewest moles of gas
Decreasing pressure shifts the equilibrium to the side with the most moles of gas

53
Q

effect of changing temperature on equilibrium

A

Increasing the temperature shifts the equilibrium in the endothermic direction
Decreasing the temperature shifts the equilibrium in the exothermic direction

chemistry (8 decks)

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