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IGCSE Chemistry > Electrochemistry > Flashcards

Electrochemistry Flashcards

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1
Q

Oxidation numbers

A

Total number of electrons that an atom gains or loses in order to form a chemical bond with another atom

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2
Q

What does it mean if a compound is not neutral

A

It is a polyatomic ion

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3
Q

Group 1 fixed oxidation number

A

+1

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4
Q

Group 2 fixed oxidation number

A

+2

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5
Q

Flourine fixed oxidation number

A

-1

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6
Q

Hydrogen with non-metal fixed oxidation state

A

+1 (hydrogen acts as the metal)

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7
Q

Hydrogen with metal or boron fixed oxidation state

A

-1 (hydrogen acts as the non metal)

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8
Q

Oxygen fixed oxidation state
Exceptions (3)

A

-2 except in H2O2 and Na2O2 where it is -1, or bonded with fluorine

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9
Q

Group 7 fixed oxidation state

A

-1 except Cl Br and I when bonded to O or F

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10
Q

What elements can have varying oxidation numbers (7)

A

Nitrogen
Phosphorus
Oxygen (H2O2, Na2O2)
Sulphur
Transition metals
Chlorine
Hydrogen

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11
Q

Applications of redox reactions/electrochemistry (3)

A

Batteries in computers
Electric cars
Remote controls

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12
Q

REDOX reactions

A

Reactions that involve the transfer of electrons
OILRIG

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13
Q

What happens when electrons are lost

A

The element/compound is oxidised and the oxidation number increases to become less negative

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14
Q

What happens when electrons are gained

A

The element/compound is reduced, the oxidation number decreases/ becomes more negative

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15
Q

Reducing agent

A

Substance that is oxidised

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16
Q

Oxidising agent

A

Substance that is reduced

17
Q

Hydrogen-oxigen fuel cells

A

Hydrogen and oxygen react in a hydrogen-oxygen fuel cell to produce electricity, water and small amounts of heat. The electrochemical converts chemical energy to electricity which is useful in cars, spacecraft and is being developed for portable electronic devices

18
Q

What is the result of hydrogen fuel cells called

A

Clean fuel

19
Q

3 equations within a hydrogen oxygen fuel cell

A
20
Q

Advantages of hydrogen fuel cells (5)

A

Renewable energy source
Plentiful cheap supply of reactants
High efficiency process (>60% compared to 33% for petrol)
Similar energy content
Produces zero carbon emmisions

21
Q

Disadvantages of hydrogen fuel cells (5)

A

Lack of facilities and methods for widespread use
Compressed gases are harardous
Reactants are gases so must be compressed for storage
Hydrogen sourced from methane uses a non-renewable source
Hydrogen sourced from water is expensive to produce

22
Q

Electrolysis

A

Decomposition of an ionic compound, when molten or in an aqueous solution by the passage of an electric current

23
Q

Positive electrode

A

Anode

24
Q

Negative electrode

A

Cathode

25
Q

Electrolyte

A

Molten/aqueous substance that undergoes electrolysis

26
Q

Describe the transfer of charge during electrolysis

A

There is movement of electrons in the external circuit from positive to negative, positively charged ions in the electrolyte move to the cathode (loses electrons) where they accept electrons. Negatively charged ions move to the anode (gains electrons) where they transfer electrons

27
Q

Why metals are electroplated

A

To improve their appearance and resistance to corrosion

28
Q

Electrode materials

A

Platinum or carbon/graphite because they are inert

29
Q

Electrolysis of lead (II) bromide

A

Insert inert electrodes made from platinum or carbon/graphite
Molten PbBr2 electrolyte
Bromide ions attracted to anode (2Br-) - bromine gas forms (brown gas bubbles) 2Br- -> Br2 + 2e
Lead ions attracted to cathode (Pb2+) - grey metal accumulates on the surface (molten lead) -> Pb2+ + 2e -> Pb

30
Q

What forms at the cathode
What forms at the anode

A

Metals + hydrogen
Non metals - hydrogen

31
Q

Identify the products formed at the electrodes and describe the observations made during the electrolysis of concentrated aqueous sodium chloride

A

Electrolyte:NaCl (aq)
Na goes to and is deposited at the cathode
Cl goes to anode (green gas bubbles)

32
Q

Identify the products formed at the electrodes and describe the observations made during the electrolysis of dilute sulfuric acid

A

Cathode : hydrogen (Bubbles)
Anode : OH (becomes water + oxygen) more dilute and bubbles

IGCSE Chemistry (21 decks)

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