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Chemistry > Electrolysis > Flashcards

Electrolysis Flashcards

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1
Q

Where do cations and anions move to when a direct current is passed through the electrolyte?

A 
Cations attracted to negative electrode (cathode)  and anions attracted to positive
c electrode (anode)
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2
Q

What discharge at cathode and anode

A

Cations discharged at cathode (metals and hydrogen gas)

Anions discharge at anode (non metals

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3
Q

What do they mean by discharging of an ion

A

It is the loss of charge of ions, which cause formation of products at cathode and anode

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4
Q

Whats electrolysis

A

thermal decomposition of the compound by driving a direct current throught the molten cmpd or soln of the compd

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5
Q

Whats battery for in electroolysis

A

Drive flow of electrons in electrolytic setup

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6
Q

Where does electron flow in fuel cell

A

The electrons flow from a more reactive metal electrode to a less reactive metal electrode

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7
Q

The ____ the two metal electrodes in the reactivity series, the greater the voltage of electric cell

A

further

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8
Q

What will be observed over time for two metal electrodes?

A

More reactive metal become smaller over time as it was oxidised and less reactive metal become “larger” as electrolyte gets reduced and form atoms on the surface of the less reactive metal

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9
Q

WHats a fuel cell

A

a device which uses a fuel to react with oxygen in air to produce electrical energy directly

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10
Q

Give the hydrogen cell equation at:

Anode electrode
Cathode electrode
overall cell equation

A

Anode elect: 2H2 –> 4H+ + 4e
Cathode elect: O2 + 4H+ + 4e –> 2H2O
overall: 2H2 + O2 –> 2H2O

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11
Q

When wire connected between copper electrode and iron electrode, in an eelctrolyte, effervescence seen on copper electrode Why?

State half eqn at iron electrode and copper electrode

A

Iron is a more metal than copper. Iron underggo oxidation and lose electrons. The electrons flow from iron to the copper electrode thru wire and into electrolyte, reducing H+ ions to hydrogen gas, and thus effervescence seen on copper electrode.

Copper elect: 2H+ + 2e- –> H2
Iron elect: FE –> Fe2+ +2e-

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12
Q

Define electrolysis

A

the conduction of electricity by an ionic compound (electrolyte), when molten or dissolved
in water, leading to the decomposition of the electrolyte

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13
Q

why can electrolyte only conduct electricity when in molten state or in soln

A

current is carried as a result of movement of ions to electrodes

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14
Q

Why cant a non electrolyte condct electricity

A

cant ionise

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15
Q

During electrolysis of PbBr2 what happens?

A

Pb2+ gather around cathode to undergo reduction, metallic lead produced
Br- gather around anode to undergo oxidation. Bromine is formed

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16
Q 
For electrolysis of PbBr2,
Anode half eqn
cathode half eqn
Overall chem eqn
Ionic eqn
A

Anode: 2Br- –> Br2 + 2e-
Cathode: Pb2+ + 2e- –> Pb
Overall: PbBr2 –> PB + Br2
Ionic: Pb2+ + 2Br- –> Pb + Br2

17
Q

Why there more than two types of ions in aqueous electroltye

A

water ionises to give hydrogen ions and hydroxide ions

18
Q

In electroplating, the object to be plated is the ________ and the metal used for plating is the _______________

A

cathode

anode

19
Q

In electroplating, the electrolyte is ____

A

a salt soln containing cations of metal that made anode

20
Q

Cations in electrochemical series (Increasing preferential discharge)

A 
K+ 
Ca
Na
Mg 
Al
Zn
Fe
Sn
Pb
H
Cu
Ag
Au
21
Q

Anions electrochemical series (increasing preferential discharge)

A 
F
SO4
NO3
Cl
Br
I
OH
22
Q

When Na+ and H+ present, which is more prefentially discharged

A

H+ ions gain electrons more readily than Na+ ions and thus H+ is more preferentially discharged

23
Q

when So4 2- and OH- present, which more preferentially discharged

A

OH- lose electrons more readily than SO4 2- ions, thus OH- is preferentiallyA discharged

24
Q

In a dilute sodium chloride as electrolyte, what is the product at cathode? [ions present: Na+, Cl-, H+ and OH-). WHY?

A

hydrogen. based on electrochemical series, H+ gain electrons more readily than Na+, thus H+ is more readily reduced: 2H+ + 2e- –> H2

25
Q

In a dilute sodium chloride as electrolyte, what is the product at anode? [ions present: Na+, Cl-, H+ and OH-). WHY?

A

oxygen. Based on electrochemical series, OH- ions loses electrons more readily than Cl-, thus OH- is perefentially oxidised: 4OH- –> O2 + 2H2O +4e-

26
Q

In a concentrated sodium chloride as electrolyte, what is the product at anode? [ions present: Na+, Cl-, H+ and OH-). WHY?

A

chlorine, The conc of Cl- is high enough for the conc effect to take place, due to closeness of position of Cl- and OH- in electrochemical series. Thus Cl- is preferentially oxidized.

2Cl- –> Cl2 +2e-

27
Q

In a concentrated sodium chloride as electrolyte, what is the product at cathode? [ions present: Na+, Cl-, H+ and OH-). WHY?

A

hydrogen. Although conc of Na+ is high, distance between positions of Na+ and H+ in electrochemical series is too great, hence H+ is still preferentially reduced 2H+ + 2e- –> H2

28
Q

what are the two active electrodes

A

copper and silver

29
Q

The more/less reactive metal ion discharge

A

less

30
Q

What happens at the copper anode in an electrolyte

A

Instead of OH- losing electrons, Cu atoms of anode lose electrons, thus copper anod dissolves:

Cu –> Cu2+ + 2e-

31
Q

why was is necessary to acidify water before electrolysis

A

Water is poor electrical conductor, Adding acid increase its conductivity by increasing conc of free mobile ions

32
Q

In practice, vol of oxygen gas collected is lesser than half of hydrogen collected (exactly half is expected). Why

A

Oxygen more soluble than hydrogen. both oxygen and hydrogen dissolve in soln but more oxygen dissolve. thus vol of oxygen collected lass than expected

33
Q

describe purification of metal (refine impure copper) with copper ii sulfate as electrolyte

A

place copper electrode as anode and pure copper as cathode. During electrolysis, the copper atoms of anode oxidise and lose electrons and Copper II ions dissolve in electrolyte. these copper ii ions migrate to cathode, gain electrons and form back as copper atoms.

Anode bcecome smaller and smaller and cathode becomes bigger

eventually impurities like other metals will ffall off to collect below anode

cocnetration of electrolyte unchanged

34
Q

Describe process of electroplation

A

During electrolysis, anode dissolves and ions thus produced migrate to cathode where they are discharged and deposited as a layer on object. conc of electrolyte remain constant

35
Q

What happenes when u want electroplate non conducting material

A

Spray with metallic pain or coat with graphite powder

36
Q

During electroplation, sodium ions reduced to form sodium atoms. Write a eqn

A

Na+ (aq) + e- –> Na (s)

Chemistry (9 decks)

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