Chemistry: Electrolysis

conductors

materials that readily allow an electric current to flow through them

non-conductors

materials that resist or inhibit a flow of electric current

metallic conduction

the flow of electricity through a metal via the metal’s negative free moving electrons

electrolytic conduction

the flow of electricity through an electrolyte, which contains dissolved or molten ions that carry the charge

electrochemical series of common metals acronym

please stop calling me a cocky zebra instead try learning how copper saves gold

cation

a positively charged ion formed from the loss of an electron from an element

anion

a negatively charged ion formed from the gain of an electron to an element

reactive metal

a metal ion that will displace a lesser reactive metal in a reaction

reactivity of elements below hydrogen

don’t really react with anything, fairly unreactive and don’t react with acids, so are used to clean copper and silverware

the most electronegative element

fluorine

electrochemical series of non-metals from highest to lowest

fluorine, sulphate, nitrate, chlorine, bromine, iodine, hydroxide

electrolysis

the chemical change (decomposition) occuring when an electric current is passed through an electrolyte

is electrolysis an endothermic reaction or exothermic reaction

endothermic, requires electric energy to begin

3 components of an electrolytic cell

anode/cathode, electrolyte, battery

anode

the positively charged electrode, negatively charged ions are attracted to this electrode

cathode

the negatively charged electrode, positively charged ions are attracted to this electrode

electrolyte

the solution through which an electric current will be passed - either a molten compound or dissolved ionic compound

where an electrolysis reaction occurs

at the electrode

what type of electrolyte is water

it is a weak electrolyte

the strength of an electrolyte is due to

the concentration of ions present in the solution

strong electrolytes

have a high concentration of ions in solution

example of strong electrolytes

strong acids, bases, and aqueous ionic/molten compounds, POLAR covalent molecules

weak electrolytes

possess a low concentration of ions when dissolved in water

examples of weak electrolytes

water, weak acids, weak bases, non polar covalent molecules — kerosene, gasoline, wax

the oxidizing agent in an electrolysis reaction

the anode

the reducing agent in an electrolysis reaction

cathode

process of electrolysis

electrodes are placed in electrolyte and power source is turned on

negatively charged ions will be attracted to the positive anode, there they donate their electrons and are discharged

these electrons flow through the anode through the wires to the cathode. the cathode becomes negatively charged and the positive ions are attracted to it

the positive ions accept the electrons from the cathode to discharge and form atoms

discharge

to go from an ion to an atom

indicator

an object used to determine if an electric current is being conducted in a solution (e.g. lightbulb)

when does an electrolysis reaction stop

when all of the ions in the solution have been discharged

what would happen in the electrolysis of lead bromide

the bromine (br2-) would head to the anode, discharge and form a brown gas and evaporate from the solution

the electrons would head to the cathode, which would then attract the lead. the lead would accept the electrons and discharge to form a metal at the bottom of the container

what would happen in the example of zinc chloride

the chloride ions would go to the anode, get discharged by donating its ions to the anode, and evaporate as a pungent light green gas

the zinc would be attracted to the cathode, accept its electrons and get discharged to form solid metal at the bottom of the container

factors that affect electrolysis

type of anode (active or inert)

position in the electrochemical series

concentration

the factors that affect electrolysis mostly pertain to

anions

active anode

an anode that is made of the same material as the metal ion in a solution

inert electrode

an anode that is not made of a metal ion in a solution

example of inert electrode

graphite, platinum, carbon

how the type of anode affects electrolysis

depending on if the anode is

active: in this case, the anode itself will ionize instead of choosing one from the solution

inert: in this case, the metal ion doesn’t have an edge over the oxygen and another factor is examined

how the concentration affects electrolysis

the ion with more concentration than the other is picked preferentially over the dilute one (usually only matters for the anion)

how the position in the electrochemical series of chemistry matters

the lower it is in the series the more likely it is to be preferentially discharged, this is because anions usually gain electrons, so it’s easier for the ones below to lose them

also applies to cations

what are some sources of errors that would occur in an electrolysis lab

impurities of electrodes

temperature changes (gas)

instrumental error (with the ammeter/voltmeter/scale

current, current’s SI unit

flow of electrons in a particular direction, each electron has a tiny charge, SI unit I

unit of current

ampere (Amps, A)

how do electrons travel

in packets

coulombs (C)

the total charge carried by a current of electrons

1 Faraday

96500 coulombs

Faraday’s constant

1 mole of electrons = 96500 coulombs

Faraday’s first law

States that the amount of substance produced at or dissolved from the electrode during an electrolysis reaction is directly proportional to the quantity of electrical charge flowing through the electrolytic cell

Faraday’s second law

The number of coulombs needed to discharge a mole of an atom is equal to the charge on the atom.

quantity of electrical charge formulas

Q =IT

C = As

how to solve quantitative electrolysis questions

write out the reaction that is being carried out

use the formula Q = IT to find coulombs taken for this SPECIFIC reaction

use formula Q = (number of electrons) x 96500 to find coulombs taken for 1 mol

cross multiply to get the moles

molar mass x moles = mass

what state will a metal be in during electrolysis

molten or liquid (l) state

real-world uses of electrolysis

metal extraction

electroplating

electrorefining

anodising

how electrolysis is used in metal extraction

a compound is added to reduce it’s melting point (cryolite - Na3AlF6)

the metal is melted down to become molten

electrodes are put into the solution and turned on

pure metal is deposited at the cathode, and a gas at the eanode

what type of elements can be extracted by electrolysis?

aluminium and above can be extracted by electrolysis

if the metal cannot be extracted by electrolysis, then how else can it be extracted?

reduction of the oxide with carbon

the apparatus used to extract a metal using carbon

blast furnace

describe the process of extracting a metal using carbon

carbon, the metal, and limestone are placed into the top of the blast furnace

hot air is pumped in through the bottom

the hot air at the bottom reacts with the carbon to form carbon dioxide, which is exothermic and heats up the furnace

the carbon dioxide rises up the furnace

as the carbon dioxide rises it reacts with more carbon to be reduced to carbon monoxide

this carbon monoxide reduces the metal oxide to just the metal

what is the purpose of limestone in the extraction of metals using carbon

it reacts with the impurities in the metal, for example silicon dioxide, to ensure majority of these impurities are removed from the extracted metal

limestone + impurities of the metal

slag

how electrolysis is used in electrorefining (purification)

the anode is the impure metal

the cathode is a very thin strip of pure metal

the electrolyte contains ions of the metal being purified

the anode ionizes itself, becoming smaller and depositing on the cathode, forming pure metal

what kind of metals can be electrorefined/electroplated?

ones lower than hydrogen in the reactivity series

how electrolysis is used in electroplating

the anode is a pure metal of the substance

the cathode is the substance that needs to be plated

the electrolyte contains the ions of the metal

the anode ionizes and deposits on the cathode, the thing that needs to be plated

how electrolysis is used in anodising

used to increase the layer of aluminium oxide on an object

anode is the aluminium object

cathode doesn’t matter

electrolyte is sulfuric acid

the object made of aluminium ionises and al3+ ions are released into the solution

the aluminium and hydroxide ions react to form a layer of aluminium oxide on the object

reasons for anodising

protects from corrosion

object can be attractively coloured as it absorbs dyes well

how to test for hydrogen

place a BURNING splint in a jar of the gas, it will combust with a squeaky pop sound

how to test for oxygen

place a GLOWING splint inside a jar of the gas, the splint will reignite

how to test for carbon dioxide

place a GLOWING splint inside a jar of the gas, it will be extinguished

haematite

an iron ore containing oxygen, impure iron ore that is purified through carbon reduction