chapter 7: electrolysis and metal extraction

Question 1

electric current

Answer 1

flow of electrons

Question 2

conductors

Answer 2

they are substances that allow electricity pass through.

Question 3

Substance having free moving electrons

Answer 3

metals: because they have free electrons

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

Question 4

substance having free moving ions

Answer 4

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

Question 5

Conduction in metals

Answer 5

involves a one-way flow of electrons

Question 6

conduction in ionic substance

Answer 6

involves a two-way flow of ions

Question 7

insulators

Answer 7

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

Question 8

electrolysis

Answer 8

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

Question 9

electrolyte

Answer 9

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

Question 10

electrodes

Answer 10

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

Question 11

electrode anode

Answer 11

positive electrode

negative charged ions move to positively charged electrode.

oxidation

Question 12

electrode cathode

Answer 12

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.

Question 13

electrolysis

Answer 13

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

Question 14

molten electrolytes
example

Answer 14

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

Question 15

half equation

Answer 15

the reaction at each electrode

Question 16

reduction easier

Answer 16

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

Question 17

Oxidation easier

Answer 17

OH-
Cl-
Br-
I-

Question 18

Inert electrodes
examples

Answer 18

like graphite and platinum

Question 19

reactive electrodes

Answer 19

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

Question 20

Electrolysis of concentrated sodium chloride solution

Answer 20

the apparatus used: Hofmann voltameter

Question 21

exp. ELECTRODE CATHODE

Answer 21

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

Question 22

exp. ELECTRODE ANODE

Answer 22

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

Question 23

Effect of electrolysis on the universal indicator

Answer 23

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

Question 24

Chlorine uses

Answer 24

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

Question 25

Hydrogen uses

Answer 25

to manufacture ammonia to manufacture margarine

Question 26

sodium hydroxide uses

Answer 26

to manufacture paper to manufacture soap to manufacture ceramics

Question 27

Electrolysis of dilute sulfuric acid

Answer 27

Dilute sulphuric acid contain three ions H+ and OH- ions are provided by the water. twice as much hydrogen than oxygen is produced

Question 28

Electrolysis of copper sulfate solution using graphite

Answer 28

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.

Question 29

Electrolysis of copper sulfate solution using copper electrodes

Answer 29

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.

Question 30

Electrolysis of copper sulfate solution using copper electrodes Explain why the blue colour of the solution doesn't change?

Answer 30

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.

Question 31

Electroplating

Answer 31

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

Question 32

Rusting

Answer 32

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.

Question 33

Investigating rusting

Answer 33

4Fe + 3O2 -> 2Fe2O3H2O

Question 34

conclusion of rusting exp

Answer 34

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

Question 35

how to prevent rusting

Answer 35

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

Question 36

protection by physical barrier

Answer 36

paint oil and grease plastic coatings electroplating

Question 37

disadvantage of physical barrier

Answer 37

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

Question 38

sacrificial protection

Answer 38

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

Question 39

sacrificial protection

Answer 39

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.

Question 40

Alloying

Answer 40

alloys are harder and more resistant to rusting than pure metals

Question 41

galvanising

Answer 41

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

Question 42

converts chemical energy into electrical energy

Answer 42

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

Question 43

Hox to increase the cell voltage

Answer 43

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

Question 44

Ores

Answer 44

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

Question 45

Steel making

Answer 45

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

Question 46

steel alloys

Answer 46

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.

Question 47

Aluminium

Answer 47

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

Question 48

Advantages of the recycling of metals

Answer 48

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