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Igcse chemistry ol > chapter 7: electrolysis and metal extraction > Flashcards

chapter 7: electrolysis and metal extraction Flashcards

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1
Q

electric current

A

flow of electrons

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2
Q

conductors

A

they are substances that allow electricity pass through.

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3
Q

Substance having free moving electrons

A

metals: because they have free electrons

graphite: because each C atom in the macromolecule also free electron)

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4
Q

substance having free moving ions

A

molten ionic compounds: they have ions that are free to move

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5
Q

Conduction in metals

A

involves a one-way flow of electrons

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6
Q

conduction in ionic substance

A

involves a two-way flow of ions

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7
Q

insulators

A

solid ionic compounds, most polymers, other macromolecules such as diamond, and simple mol like water or methane not having free electrons or ions.

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8
Q

electrolysis

A

it’s the breakdown of an ionic compounds when molten or aq by the action of electricity.

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9
Q

electrolyte

A

the liquid used to transfer electric current. It’s a molten or aq ionic compound

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10
Q

electrodes

A

are the solid conductors that transfer electric current from the battery to the liquid. they are either made of graphite or metals

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11
Q

electrode anode

A

positive electrode

negative charged ions move to positively charged electrode.

oxidation

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12
Q

electrode cathode

A

negative electrode

metals ions and hydrogen ions move to the negative electrode

reduction

if metal atoms are formed, they are deposited on the electrode. if hydrogen molecules are formed, they are given off a gas.

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13
Q

electrolysis

A

endothermic process
breakdown of ionic compound when molten or aq by action of electricity

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14
Q

molten electrolytes
example

A

the electrode: graphite is mainly used in molten electrolysis because
its good electricity conductor
has high melting point
intert and cheap

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15
Q

half equation

A

the reaction at each electrode

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16
Q

reduction easier

A

K+
Na+
Ca2+
Mg2+
Al3+
Zn2+
Fe3+
Sn2+
Pb2+
H+
Cu2+
Ag+

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17
Q

Oxidation easier

A

OH-
Cl-
Br-
I-

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18
Q

Inert electrodes
examples

A

like graphite and platinum

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19
Q

reactive electrodes

A

that could be made of metals, take part in the reaction

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20
Q

Electrolysis of concentrated sodium chloride solution

A

the apparatus used: Hofmann voltameter

21
Q

exp. ELECTRODE CATHODE

A

the 2 positive ions are attracted to the negatively charged electrode.
since hydrogen is below sodium reactivity series, hydrogen ions are easier to reduce that sodium ions. reduction to form hydrogen atoms. the hydrogen atoms immediately combine to form hydrogen molecules (H2)

Observation: bubbles of colorless gas

22
Q

exp. ELECTRODE ANODE

A

the 2 negative ions are attached to the positively charged anode. Since the chloride ions are easier to oxidized than hydroxide ions, they lose electrons (oxidation) to form chlorine atoms. the chlorine atoms immediately combine molecules (Cl2)

Observation: bubbles of greenish yellow chlorine gas

23
Q

Effect of electrolysis on the universal indicator

A

the initial colour of universal indicator in the voltameter is green, because sodium chloride solution is neutral.

At cathode: when hydrogen ions are removed, this leaves an excess of OH- ions in this area. so indicator changes colour to purple.

At anode: chlorine is formed. colorless

24
Q

Chlorine uses

A

to kill bacteria in water and swimming pool
to manufacture HCl
to manufacture bleaching agent
to manufacture the plastic

25
Q

Hydrogen uses

A

to manufacture ammonia
to manufacture margarine

26
Q

sodium hydroxide uses

A

to manufacture paper
to manufacture soap
to manufacture ceramics

27
Q

Electrolysis of dilute sulfuric acid

A

Dilute sulphuric acid contain three ions H+ and OH- ions are provided by the water.

twice as much hydrogen than oxygen is produced

28
Q

Electrolysis of copper sulfate solution using graphite

A

when graphite electrodes are used, copper sulfate solution undergoes electrolysis to produce copper metal at the cathode and hydrogen gas forms at the anode.

Dilute copper sulfate contains four ions Cu2+ and SO4 ions are provided by copper sulphate, and H+ and OH- ions are provided by the water.

29
Q

Electrolysis of copper sulfate solution using copper electrodes

A

If we change the electrodes from graphite to copper a different process takes place. this process is used commercially to refine impure copper.

As copper ions move from the anode to the cathode the anode gets smaller as the cathode gets bigger. this is a redox reaction.

30
Q

Electrolysis of copper sulfate solution using copper electrodes

Explain why the blue colour of the solution doesn’t change?

A

The rate at which the copper is oxidized at the anode is the same as the rate at which the copper ions are reduced at the cathode.

The concentration of the copper sulphate solution remains unchanged.

31
Q

Electroplating

A

it is covering the iron or any reactive metal with layer of a less reactive metal by electrolysis to:

1-protect the metal from corrosion
2-gives the metal a shiny appearance

32
Q

Rusting

A

the general reaction of metals with oxygen to form a metal oxide os called corrosion.

when iron or steel corrodes we give it the specific name of rusting.

the brown flakes of rust are weak and brittle this cause them to crumble and break away.

33
Q

Investigating rusting

A

4Fe + 3O2 -> 2Fe2O3H2O

34
Q

conclusion of rusting exp

A

Rust was only found in test tube of water and air demonstrating that both are needed for rusting to occur.

sodium chloride speed up the rusting

35
Q

how to prevent rusting

A

1 use physical barrier to keep air and water out

2 sacrificial protection involves attaching more reactive metal to the iron

3 alloying

4cathodic protection

36
Q

protection by physical barrier

A

paint
oil and grease
plastic coatings
electroplating

37
Q

disadvantage of physical barrier

A

they need to be maintained if they are scratched or broken the metal will rust

38
Q

sacrificial protection

A

by attaching a more reactive element like Mg or zn which reacts instead of iron.

39
Q

sacrificial protection

A

1 Zinc is more reactive than iron
2 it loses electrons faster
3 electrons are lose by zinc are gained by iron.
4 this mean that zinc reacts with oxygen leaving iron unreacted.

40
Q

Alloying

A

alloys are harder and more resistant to rusting than pure metals

41
Q

galvanising

A

is another way of using zinc to protect iron by completely coating iron or steel with a layer of zinc. is methode oof combines machinal barrier and sacrificial protection

42
Q

converts chemical energy into electrical energy

A

a strip of reactive metal
a strip of a less reactive metal
both dipped in an aq sol of an ionic compound ex: sodium chloride

43
Q

Hox to increase the cell voltage

A

1 increase the difference in reactivity between the 2 metals
2 increase the conc of the used electrolyte

44
Q

Ores

A

are rocks which contain a high conc of a metal that needs to be extracted.
ex: ZnS

45
Q

Steel making

A

1 pure hot jet of oxygen is blown into the molten iron obtained from the blast furnace
2 carbon reacts with oxygen and is converted to carbon dioxide and carbon monoxide gases and escape.
3 other non-metal impurities are converted into other acidic oxides.
4 Lime is added to the pig iron. it reacts with the acidic oxides in a neutralization reaction to produce a layer of a slag that can be easily removed from the surface of iron

46
Q

steel alloys

A

the addition of small quantities of other metals oe carbon alters the properties of steel.

1 steel
2 stainless steel is an alloy containing chromium and nickel, which is hard and resistant to corrosion. it is used to make cutlery
3 mild steel is soft and easily shaped.

47
Q

Aluminium

A

it is a reactive metal. since it is above carbon in the reactivity series. it cannot be extracted by carbon reduction.

48
Q

Advantages of the recycling of metals

A
  • saving metal ores
    -recycling uses much less energy than the primary extraction process
    -steel and iron are easily recycled because the are magnetic.

Igcse chemistry ol (8 decks)

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