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chemistry > elements of the sea > Flashcards

elements of the sea Flashcards

(54 cards)

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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

22
Q

oxidation state rule for atoms in elements

23
Q

relationship between oxidation state and oilrig

Study These Flashcards
A

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

24
purpose of iodine thiosulfate titrations
to find the concentration of an oxidising agent, e.g. iodate
25
process of iodine thiosulfate titrations
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
appearance of fluorine
gas at room temp pale yellow colour
27
appearance of chlorine
gas at room temp greenish yellow
28
appearance of bromine
liquid at room temp reddish brown
29
appearance of iodine
solid at room temp grey-black colour
30
general properties of halogens
highly reactive non-metals diatomic not very soluble (covalent + non-polar)
31
halogen trends
as you go down the group - boiling and melting point increases - volatility decreases (due to stronger id-id bonds) - reactivity decreases
32
reactivity of halogens
- 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
aqueous chlorine colour
colourless
34
aqueous bromine colour
orange
35
aqueous iodine colour
brown
36
halide ions + silver ions
chlorine - white precipitate bromine - cream precipitate iodine - yellow precipitate
37
silver halides + ammonia
silver chloride - dissolves in dilute ammonia silver bromide - dissolves in concentrated ammonia silver iodide - insoluble in ammonia
38
making hydrogen halides with sulfuric acid
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
hydrogen halides when heated
HF and HCl -> stable + won't break HBr -> will slightly dissociate HI -> will fully dissociate
40
hydrogen halides with water
HF -> doesn't fully dissociate in water, making it a weak acid HCl, HBr, HI -> fully dissociates in water, strong acid
41
hydrogen halides with ammonia
forms ammonium halide NH4X (aq)
42
hydrogen halides with sulfuric acid
HF and HCl -> do not react with sulfuric acid HBr -> Br2 + SO2 + H2O HI -> I2 + H2S + H2O
43
risks of chlorine
a toxic gas, corrosive, irritates the respiratory system, risk of fires (oxidising agent)
44
transportation of chlorine
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
uses of chlorine
sterilising water in bleach removes stains
46
criteria for dynamic equilibrium
- 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
equilibrium constant
Kc described position of reaction at equilibrium temperature dependent
48
if Kc is greater than 1
there is a greater concentration of products over reactants at equilibrium
49
if Kc is less than 1
there is a greater concentration of reactants over products at equilibrium
50
Kc expression
aA + bB <=> cC dD Kc = ([C]^c [D]^d) / ([A]^a [B]^b Kc = [products] / [reactants]
51
calculating Kc with correct units method
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
effect of changing pressure on equilibrium
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
effect of changing temperature on equilibrium
Increasing the temperature shifts the equilibrium in the endothermic direction Decreasing the temperature shifts the equilibrium in the exothermic direction

chemistry (12 decks)

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