HOME PAGE * KS3 SCIENCES * GCSE BIOLOGY  CHEMISTRY  PHYSICS * ADVANCED LEVEL CHEMISTRY

School Chemistry notes: Summary of electrode equations you need to know

IGCSE AQA GCSE Chemistry A level Edexcel GCSE Chemistry A level OCR Gateway Science Chemistry A level OCR 21st Century Science Chemistry

SUMMARY of electrode half-equations and products

 Doc Brown's chemistry revision notes: GCSE chemistry, IGCSE  chemistry, O level & ~US grades 9-10 school science courses or equivalent for ~14-16 year old students of chemistry Science AQA GCSE chemistry Edexcel GCSE Chemistry OCR 21st Century Chemistry OCR Gateway Chemistry

ELECTROCHEMISTRY revision notes on electrolysis, cells, experimental methods, apparatus, batteries, fuel cells and industrial applications of electrolysis

8. Summary of electrode reactions and products

A whole series of typical electrode reactions you are likely to come across in school & college course e.g. GCSE/IGCSE/O Level and basic A level chemistry courses too. These revision notes and summary of electrode equations products should prove useful for the new AQA chemistry, Edexcel chemistry & OCR chemistry GCSE (9–1, 9-5 & 5-1) science courses.

ELECTROCHEMISTRY INDEX

[SEARCH BOX

8. Summary of the products of the electrolysis of various electrolytes

What are the products of the electrolysis of molten aluminium oxide, aqueous copper sulphate solution, aqueous sodium chloride solution (brine), hydrochloric acid, sulphuric acid, molten lead(II) bromide, molten calcium chloride? add overall equations?

Electrolyte

solution or melt

negative cathode product negative electrode

cathode half-equation

positive anode product positive electrode

anode half-equation

comments
molten aluminium oxide

Al2O3(l)

molten aluminium Al3+(l) + 3e– ==> Al(l) oxygen gas

2O(l) – 4e– ==> O2(g)

or  2O(l)  ==> O2(g) + 4e–

The industrial method for the extraction of aluminium its ore
aqueous copper(II) sulfate

CuSO4(aq)

copper deposit any conducting electrode e.g. carbon rod, any metal including copper itself

Cu2+(aq) + 2e– ==> Cu(s)

oxygen gas inert electrode like carbon (graphite rod) or platinum

(i) 4OH–(aq) – 4e– ==> 2H2O(l) + O2(g)

or  4OH–(aq) ==> 2H2O(l) + O2(g) + 4e–

(ii) 2H2O(l) – 4e– ==> 4H+(aq) + O2(g)

or 2H2O(l) ==> 4H+(aq) + O2(g) + 4e–

The blue colour of the copper ion will fade as the copper ions are converted to the copper deposit on the cathode
aqueous copper (II) sulphate

CuSO4(aq)

copper deposit any conducting electrode e.g. carbon rod, any metal including copper itself

Cu2+(aq) + 2e– ==> Cu(s)

copper(II) ions – the copper anode dissolves copper anode

Cu(s) – 2e– ==> Cu2+(aq)

or  Cu(s) ==> Cu(s) + 2e–

This is the basis of the method of electroplating any conducting solid with a layer of copper. When using both copper cathode and anode, the blue colour of the copper ion does not decrease because copper deposited at the (–) cathode = the copper dissolving at the (+) anode.
Copper(II) chloride

CuCl2(aq)

copper deposit Cu2+(aq) + 2e– ==> Cu(s) chlorine gas

2Cl–(aq) – 2e– ==> Cl2(g)

 or  2Cl–(aq) ==> Cl2(g) + 2e– 

molten sodium chloride

NaCl(l)

molten sodium Na+(l) + e– ==> Na(l) chlorine gas

2Cl–(l) – 2e– ==> Cl2(g)

 or  2Cl–(l) ==> Cl2(g) + 2e–

This a method used to manufacture sodium and chlorine.
aqueous sodium chloride solution (brine)

NaCl(aq)

hydrogen

2H+(aq) + 2e– ==> H2(g)

or 2H3O+(aq) + 2e– ==> H2(g) + 2H2O(l)

or 2H2O(l) + 2e– ==> H2(g) + 2OH–(aq)

chlorine gas

2Cl–(aq) – 2e– ==> Cl2(g)

 or  2Cl–(aq) ==> Cl2(g) + 2e–

This is the process by which hydrogen, chlorine and sodium hydroxide are manufactured
hydrochloric acid

HCl(aq)

hydrogen gas 2H+(aq) + 2e– ==> H2(g)

or 2H3O+(aq) + 2e– ==> H2(g) + 2H2O(l)

chlorine gas

2Cl–(aq) – 2e– ==> Cl2(g)

 or  2Cl–(aq) ==> Cl2(g) + 2e– 

All acids give hydrogen at the cathode.

Theoretically the gas volume ratio is H2:Cl2 is 1:1, BUT, chlorine is slightly so there seems less chlorine formed than actually was.

sulphuric acid

sulfuric acid

H2SO4(aq)

hydrogen gas 2H+(aq) + 2e– ==> H2(g)

or 2H3O+(aq) + 2e– ==> H2(g) + 2H2O(l)

oxygen gas

(i) 4OH–(aq) – 4e– ==> 2H2O(l) + O2(g)

or  4OH–(aq) ==> 2H2O(l) + O2(g) + 4e–

(ii) (+) 2H2O(l) – 4e– ==> 4H+(aq) + O2(g)

or 2H2O(l) ==> 4H+(aq) + O2(g) + 4e– 

All acids give hydrogen at the cathode. Whereas hydrochloric acid gives chlorine at the anode, the sulfate ion does nothing and instead oxygen is formed. This is the classic 'electrolysis of water'.

Theoretically the gas volume ratio is H2:O2 is 2:1 which you see with the Hofmann Voltammeter

molten lead(II) bromide

PbBr2(l)

molten lead Pb2+(l) + 2e– ==> Pb(l) bromine vapour

2Br–(l) – 2e– ==> Br2(g)

 or  2Br–(l) ==> Br2(g) + 2e–

A good demonstration in the school laboratory – brown vapour and silvery lump provide good evidence of what's happened
molten calcium chloride

CaCl2(l)

solid or molten calcium Ca2+(l) + 2e– ==> Ca(s) chlorine gas

2Cl–(aq) – 2e– ==> Cl2(g)

 or  2Cl–(aq) ==> Cl2(g) + 2e–

The basis of the industrial method for the manufacture of calcium metal
Molten anhydrous zinc chloride

ZnCl2(l)

solid zinc Zn2+(l) + 2e– ==> Zn(s)

 

chlorine gas

2Cl–(aq) – 2e– ==> Cl2(g)

 

A good demonstration in the school laboratory - safer than using lead bromide
Silver nitrate

AgNO3(aq)

solid silver

Ag+(aq) + 2e– ==> Ag(s)

oxygen gas

4OH–(aq) – 4e– ==> 2H2O(l) + O2(g)

electroplating experiment
Sodium bromide

 NaBr(aq)

hydrogen gas 2H+(aq) + 2e– ==> H2(g)  

2Br–(aq) – 2e– ==> Br2(aq)

School experiment
Potassium iodide

KI(aq)

hydrogen gas 2H+(aq) + 2e– ==> H2(g)  

2I–(aq) – 2e– ==> I2(aq/s)

School experiment
Sulfate salts of reactive metals > hydrogen theoretically hydrogen gas 2H+(aq) + 2e– ==> H2(g)  

4OH–(aq) – 4e– ==> 2H2O(l) + O2(g)

School experiment

Similar results with most nitrate salts of reactive metals

           
**************** ************ **************************************************** ********** ******************************************************* *************************************

9. A shorter summary of electrode reactions (half-equations) and products

 

 

 

Equation

reference

number

(–) negative cathode electrode where reduction of the attracted positive cations is by electron gain to form metal atoms or hydrogen [from Mn+ or H+, n = numerical positive charge]. The electrons come from the positive anode (see below).

(+) positive anode electrode where the oxidation of the atom or anion is by electron loss. Non–metallic negative anions are attracted and may be oxidised to the free element. Metal atoms of a metal electrode can also be oxidised to form positive metal ions which pass into the liquid electrolyte. The released electrons move round in the external part of the circuit to produce the negative charge on the cathode electrode.

So, before each electrode equation is a (–) for a negative cathode electrode = a reduction reaction equation or a (+) for a positive anode electrode = an oxidation reaction equation

The electrode half-equations are shown on the left with examples of industrial processes where this electrode reaction happens on the right. Unless otherwise stated, the electrodes are inert i.e. they do not chemically change e.g. platinum or carbon–graphite.

 PLEASE NOTE – all electrode equations are a summary–simplification of what happens on an electrode surface in electrolysis. There may be e.g. two equations which are totally equivalent to each other to describe WHAT IS ACTUALLY FORMED e.g. the formation of hydrogen or oxygen and in some cases other products may be formed too.

1

a reduction electrode reaction

(–) Na+(l) + e– ==> Na(l) (sodium metal)

sodium ion reduced to sodium metal atoms: typical of electrolysis of molten chloride salts to make chlorine and the metal
2

an oxidation electrode reaction

(+) 2Cl–(l/aq) – 2e– ==> Cl2(g)

 or  2Cl–(l/aq) ==> Cl2(g) + 2e–

Note that you can write these anode oxidation reactions either way round.

chloride ion oxidised to chlorine gas molecules: electrolysis of molten chloride salts(l) or their concentrated aqueous solution(aq) or conc. hydrochloric acid(aq) to make chlorine
3

a reduction electrode reaction

(–) 2H+(aq) + 2e– ==> H2(g) (hydrogen gas)

or 2H3O+(aq) + 2e– ==> H2(g) + 2H2O(l)

or 2H2O(l) + 2e– ==> H2(g) + 2OH–(aq)

All three equations amount to the same overall change i.e. the formation of hydrogen gas molecules and as far as I know any is acceptable in an exam?

hydrogen ion or water reduced to hydrogen gas molecules: electrolysis of many salt or acid solutions to make hydrogen
4

a reduction electrode reaction

(–) Cu2+(aq) + 2e– ==> Cu(s) (copper deposit)

copper(II) ion reduced to copper atoms: deposition of copper in its electrolytic purification or electroplating using copper(II) sulphate solution, electrode can be copper or other metal to be plated
5

an oxidation electrode reaction

(+) Cu(s) – 2e– ==> Cu2+(aq) (copper dissolves)

or  Cu(s) ==> Cu(s) + 2e–

copper atoms oxidised to copper(II) ions: dissolving of copper in its electrolytic purification or electroplating (must have positive copper anode)
6

a reduction electrode reaction

(–) Al3+(l) + 3e– ==> Al(l) (aluminium)

aluminium ions reduced to aluminium atoms: extraction of aluminium in the electrolysis of its molten oxide ore(l) 
7

an oxidation electrode reaction

(+) 2O(l) – 4e– ==> O2(g) (oxygen gas)

or  2O(l)  ==> O2(g) + 4e–

oxide ion oxidised to oxygen gas molecules: electrolysis of molten oxides e.g. anode reaction in the extraction of aluminium from molten bauxite.
8

an oxidation electrode reaction

(i) (+) 4OH–(aq) – 4e– ==> 2H2O(l) + O2(g) (oxygen gas)

or  4OH–(aq) ==> 2H2O(l) + O2(g) + 4e–

(ii) (+) 2H2O(l) – 4e– ==> 4H+(aq) + O2(g) (oxygen gas)

or 2H2O(l) ==> 4H+(aq) + O2(g) + 4e–

Both equations amount to the same overall change i.e. the formation of oxygen gas molecules and as far as I know either is acceptable in an exam?

There are two equations that describe the formation of oxygen in the electrolysis of water.

hydroxide ions or water molecules are oxidised to oxygen gas molecules: electrolysis of many salt solutions such as sulphates, sulphuric acid etc. gives oxygen (chlorides ==> chlorine in concentrated solution, but can also give oxygen in diluted solution)

9

 a reduction electrode reaction

(–) Pb2+(l) + 2e– ==> Pb(l) (lead deposit)

lead(II) ions reduced to lead atoms: electrolysis of molten lead(II) bromide(l) 
10

an oxidation electrode reaction

(+) 2Br–(l/aq) – 2e– ==> Br2(g/l) (bromine)

or  2Br– ==> Br2 + 2e–

bromide ions oxidised to gas/liquid bromine molecules: electrolysis of molten bromide salts(l) or their concentrated aqueous solution(aq) or conc. hydrobromic acid(aq) to make bromine
11

a reduction electrode reaction

(–) Zn2+(aq) + 2e– ==> Zn(s) (zinc deposit)

zinc ions reduced to zinc atoms: galvanising steel (the electrode) by electroplating from aqueous zinc sulphate solution, (or from molten zinc chloride?)
12

a reduction electrode reaction

(–) Ag+(aq) + e– ==> Ag(s) (silver deposit)

silver ions reduced to silver atoms: silver electroplating from silver salt solution(aq), electrode can be other metal
13

a reduction electrode reaction

(–) Ca2+(l) + 2e– ==> Ca(s) (calcium metal)

calcium ions reduced to calcium atoms e.g. in molten calcium chloride or bromide etc.
***** ******************************************************************************* ***************************************************************

TOP OF PAGE

ELECTROCHEMISTRY INDEX:  1. INTRODUCTION to electrolysis - electrolytes, non-electrolytes, electrode equations, apparatus 2. Electrolysis of acidified water (dilute sulfuric acid) and some sulfate salts and alkalis 3. Electrolysis of sodium chloride solution (brine) and bromides and iodides 4. Electrolysis of copper(II) sulfate solution and electroplating with other metals e.g. silver 5. Electrolysis of molten lead(II) bromide (and other molten ionic compounds) 6. Electrolysis of copper(II) chloride solution 7. Electrolysis of hydrochloric acid 8. Summary of electrode equations and products 9. Summary of electrolysis products from various electrolytes 10. Simple cells (batteries) 11. Fuel Cells e.g. the hydrogen - oxygen fuel cell 12. The electrolysis of molten aluminium oxide - extraction of aluminium from bauxite ore & anodising aluminium to thicken and strengthen the protective oxide layer 13. The extraction of sodium from molten sodium chloride using the 'Down's Cell' 14. The purification of copper by electrolysis 15. The purification of zinc by electrolysis 16. Electroplating coating conducting surfaces with a metal layer 17. Electrolysis of brine (NaCl) for the production of chlorine, hydrogen & sodium hydroxide AND 18. Electrolysis calculations

[SEARCH BOX]


Electrolysis Quiz (GCSE 9-1 HT Level (harder)

Electrolysis Quiz (GCSE 9-1 FT Level (easier)


information on summary of electrodes and electrode equations KS4 Science summary of electrodes and electrode equations GCSE chemistry guide notes on summary of electrodes and electrode equations for schools colleges academies science course tutors images pictures diagrams of apparatus for summary of electrodes and electrode equations investigations word balanced symbol equations of summary of electrodes and electrode equations science chemistry revision notes on summary of electrodes and electrode equations revising the chemistry of summary of electrodes and electrode equations help in chemical understanding of summary of electrodes and electrode equations description of summary of electrodes and electrode equations experiments for chemistry courses university courses in chemistry careers in chemistry jobs in the chemical industry laboratory assistant apprenticeships in chemistry technical internship in chemistry IGCSE chemistry summary of electrodes and electrode equations USA US grade 8 grade 9 grade10 summary of electrodes and electrode equations chemistry explanations of summary of electrodes and electrode equations information on summary of electrolysis products KS4 Science summary of electrolysis products GCSE chemistry guide notes on summary of electrolysis products for schools colleges academies science course tutors images pictures diagrams of apparatus for summary of electrolysis products investigations word balanced symbol equations of summary of electrolysis products science chemistry revision notes on summary of electrolysis products revising the chemistry of summary of electrolysis products help in chemical understanding of summary of electrolysis products description of summary of electrolysis products experiments for chemistry courses university courses in chemistry careers in chemistry jobs in the chemical industry laboratory assistant apprenticeships in chemistry technical internship in chemistry IGCSE chemistry summary of electrolysis products USA US grade 8 grade 9 grade10 summary of electrolysis products chemistry explanations of summary of electrolysis products summary of electrolysis products for AQA AS chemistry, summary of electrolysis products for Edexcel A level AS chemistry, summary of electrolysis products for A level OCR AS chemistry A, summary of electrolysis products for OCR Salters AS chemistry B, summary of electrolysis products for AQA A level chemistry, summary of electrolysis products for A level Edexcel A level chemistry, summary of electrolysis products for OCR A level chemistry A, summary of electrolysis products for A level OCR Salters A level chemistry B summary of electrolysis products for US Honours grade 11 grade 12 summary of electrolysis products for pre-university chemistry courses pre-university A level revision notes for summary of electrolysis products  A level guide notes on summary of electrolysis products for schools colleges academies science course tutors images pictures diagrams for summary of electrolysis products A level chemistry revision notes on summary of electrolysis products for revising module topics notes to help on understanding of summary of electrolysis products university courses in science careers in science jobs in the industry laboratory assistant apprenticeships technical internships USA US grade 11 grade 11 AQA A level chemistry notes on summary of electrolysis products Edexcel A level chemistry notes on summary of electrolysis products for OCR A level chemistry notes WJEC A level chemistry notes on summary of electrolysis products CCEA/CEA A level chemistry notes on summary of electrolysis products for university entrance examinations  GCSE chemistry IGCSE chemistry revision notes on summary of electrolysis products KS4 GCSE Science revision notes on summary of electrolysis products GCSE chemistry guide notes on summary of electrolysis products for schools colleges academies science course tutors images pictures diagrams for summary of electrolysis products science chemistry revision notes on summary of electrolysis products for revising chemistry module topics notes to help on understanding of summary of electrolysis products university courses in science careers in science jobs in the industry laboratory assistant apprenticeships technical internships USA US grade 8 grade 9 grade10 AQA chemistry science GCSE notes on summary of electrolysis products Edexcel chemistry science notes on summary of electrolysis products for OCR 21st century chemistry science notes on summary of electrolysis products OCR GCSE Gateway science chemistry notes on summary of electrolysis products WJEC gcse science chemistry notes on summary of electrolysis products CCEA/CEA gcse chemistry notes science O level chemistry notes for summary of electrolysis products IGCSE chemistry revision notes on summary of electrolysis products O level chemistry notes should prove useful for the new AQA chemistry, Edexcel chemistry & OCR chemistry GCSE (9–1, 9-5 & 5-1) science courses gcse chemistry revision free detailed notes on summary of electrolysis products to help revise igcse chemistry igcse chemistry revision notes on summary of electrolysis products O level chemistry revision free detailed notes on summary of electrolysis products to help revise gcse chemistry free detailed notes on summary of electrolysis products to help revise O level chemistry free online website to help revise summary of electrolysis products for gcse chemistry  free online website to help revise summary of electrolysis products for igcse chemistry free online website to help revise O level summary of electrolysis products chemistry how to succeed in questions on summary of electrolysis products for gcse chemistry how to succeed at igcse chemistry how to succeed at O level chemistry a good website for free questions on summary of electrolysis products to help to pass gcse chemistry questions on summary of electrolysis products a good website for free help to pass igcse chemistry with revision notes on summary of electrolysis products a good website for free help to pass O level chemistry GCSE (9–1, 9-5 & 5-1) science courses

Doc Brown's School Science Website - KS3 Sciences + GCSE/IGCSE Sciences + Advanced A Level Chemistry

TOP OF PAGE

[SEARCH BOX]

Website content © Dr Phil Brown 2000+. All copyrights reserved on revision notes, images, quizzes, worksheets etc. Copying of website material is NOT permitted. Exam revision summaries & references to science course specifications are unofficial.

ELECTROCHEMISTRY INDEX

best high street shop or best online deals currys pc world combined science trilogy AQA GCSE chemistry revision notes argos amazon john lewis dell acer samsung raycon bose sony asus huawei HP microsoft in-ear headphones earbuds ipad combined science Edexcel GCSE chemistry revision notes desktop computer laptop computer for school college university students Oxford-AQA IGCSE chemistry revision notes latest video games consoles apple iphone google combined science OCR GCSE Gateway Science chemistry A revision notes high end mobile phones cell phone bargain smartphone xiaomi oppo high tech products combined science OCR GCSE Twenty First Century Science chemistry B revision notes latest fashion in trainers OCR Cambridge IGCSE chemistry revision notes latest fashion in shoes latest fashion in mobile phones cell phones Edexcel IGCSE chemistry revision notes

 Doc Brown's Chemistry 

*

best  gift deals latest video game release, half-equations used to describe electrolysis best  gift deals best bargains in summary of electrode equations for electrolysis AQA GCSE chemistry shop sales latest pop music releases, summary of electrode equations for electrolysis best  sales deals download free music, latest film releases, best  gifts for teenagers latest high street fashion in clothes, fashionable trending in clothing, best  gift deals best bargains in   shop salesgirls buy clothes, spend a lot of money on clothes, summary of the products from electrolysis OCR 21st Century science GCSE chemistry best  sales deals shoes, summary of the products from electrolysis sweets and chocolates, magazines and make-up best  gifts for teenagers half-equations used to describe electrolysis Edexcel GCSE chemistry Boys buy food and drink, computer games best  gift deals best bargains in   shop sales DVDs and CDs, summary of electrode equations for electrolysis girls and boys spend a lot of money on credit for mobile phones best  sales deals best bargains in  shop sales buses and trains to transport them going out best  gifts for teenagers best bargains in summary of electrode equations for electrolysis OCR Gateway science GCSE chemistry shop sales best high street shop or best online deals currys pc world argos amazon john lewis dell acer samsung raycon bose sony asus huawei HP microsoft in-ear headphones earbuds ipad desktop computer laptop computer for school college university students latest video games consoles apple iphone google high end mobile phones cell phone bargain smartphone xiaomi oppo Girls spend a lot of money on clothes best  gift deals  color colour preferences in clothes, summary of the products from electrolysis cool sunglasses best sales deals summary of the products from electrolysis boys buy expensive things like best  gifts for teenagers designer sports clothes and trainers, teenagers save for holidays, half-equations used to describe electrolysis best  sales deals clothes, mobile phones, birthday presents and electronic goods, summary of electrode equations for electrolysis teenage accessories, Favourite style of jeans. best  gifts for teenagers A typical girl’s shopping list includes mobile phone credit deals best half-equations used to describe electrolysis OCR 21st Century science GCSE chemistry gift deals fashionable quality cool airpods, summary of the products from electrolysis air pods, fashionable clothes best  sales deals the most popular favourite sneakers best  gifts for teenagers fancy shoes, sweets, chocolates, magazines, best  gift deals best bargains in   shop sales lip moisturizer best bargains in   shop sale slots on make-up, summary of the products from electrolysis AQA GCSE chemistry well being, teenage decor decorating their room best  sales deals summary of electrode equations for electrolysis teenagers like LED string lantern lights, best  gifts for teenagers beauty products for teenagers, half-equations used to describe electrolysis denim jackets, scrunchies coolness, fashionable back packs, half-equations used to describe electrolysis Edexcel GCSE chemistry typical boy’s shopping list includes mobile credit deals, eating out takeaway food and drinks, what teenagers like to buy in clothes best  gifts for teenagers computer games, DVDs, CDs, summary of the products from electrolysis what teenagers talk about best  gift deals what teenagers worry about, summary of electrode equations for electrolysis OCR Gateway science GCSE chemistry what teenagers like to do for fun sports best  sales deals, half-equations used to describe electrolysis  what cool things do teenagers buy, resale websites like eBay Teenager

TOP OF PAGE and sub-index