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

Revision notes chemical equilibrium - electrolysis & significance of electrochemical series Advanced Level Theoretical-Physical Chemistry

AQA Advanced A level Chemistry Edexcel Advanced A level Chemistry OCR Advanced A level Chemistry A OCR Salters Advanced A level Chemistry B

Doc Brown's A Level Chemistry Revision Notes

Theoretical–Physical Advanced Level Chemistry – Equilibria – Chemical Equilibrium Revision Notes PART 7.6

7.6 Electrolysis and the electrochemical series

What is electrolysis?

What is the relationship between electrolysis products and the electrochemical series?

Chemical Equilibrium Notes Part 7 Index



7.6 Electrolysis and the electrochemical series

  • Right at the start, in 7.2 Simple cells notation and construction, it was pointed out that electrode potentials are based on equilibria such as ...

    • Cu2+(aq) + 2e (c) doc b Cu(s)

  • Since these reactions are reversible, they can be used 'spontaneously' in cells to generate electrical energy via the overall redox reaction BUT the reverse process can be 'enforced' in electrolysis by applying a potential difference ('voltage') across a suitable aqueous solution or molten compound.

  • The GCSE notes on the Extra Electrochemistry page contains most of the electrolysis details you need for advanced level, and the details are not replicated here, but there are some other points to make, which are outlined below.

  • The electrochemical series of half–cell reaction potentials, can be used to predict which ions are likely to be preferentially discharged to form electrolysis products on the cathode(+ pole in electrolysis) or anode (+ pole in electrolysis).

    • At the negative (–) cathode electrode (reduction half reaction)

      • The more positive/less negative the half–cell potential, the more easily the cation is discharged by reduction.

      • e.g. copper metal from copper(II) ions (+0.34V) will be discharged deposited on a cathode preferentially from iron from iron(II) ions (–0.44V) from a solution containing both ions.

      • Since the process involves electron gain, the cation with the greatest potential to gain electrons is the one that is preferentially discharged

      • i.e. Cu2+(aq) + 2e ==> Cu(s) occurs more readily than Fe2+(aq) + 2e ==> Fe(s)

    • At the positive (+) anode electrode (oxidation half reaction)

      • The less positive the half–cell potential, the more easily the anion is discharged by oxidation.

      • e.g. in an aqueous mixture of bromide and chloride ions, bromide forms bromine (+1.09V) more readily than chloride ion forms chlorine (+1.36V).

      • Since the process involves electron loss, the ion which is the most readily formed will be the ion which is least readily discharged.

      • i.e. 2Br(aq) ==> Br2(aq) + 2e occurs more readily than 2Cl(aq) ==> Cl2(aq) + 2e

    • But sometimes other factors come into consideration e.g.

      • Concentrated or dilute sodium chloride solution (brine)

      • In concentrated NaCl(aq) evolution of chlorine predominates from 2Cl(aq) ==> Cl2(aq) + 2e

      • but in very dilute NaCl(aq) evolution of oxygen predominates from 4OH(aq) ==> O2(g) + 2H2O(l) + 4e

      • Theoretically oxygen should be discharged first, but the hydroxide ion concentration is so low compared to the chloride ion that little oxygen is produced on anode–ion collision probability. Also, oxygen has a high 'overpotential' (which you can equate to a high activation energy giving a very slow rate of reaction

      • ) which also inhibits its formation.

    • There will be differences in electrolysis products between molten salts and aqueous solutions due to the presence of water.

      • e.g. molten sodium chloride gives sodium at the (–) cathode but the aqueous solution gives hydrogen. In both cases chlorine is formed at the (–) cathode electrode.

    • There will be differences in electrolysis products between inert and non–inert electrodes.

      • e.g. copper(II) sulphate solution gives oxygen gas at the (–) anode if it is inert platinum/carbon, but a copper anode dissolves giving the copper(II) ion. In both cases copper metal is deposited on the (–) cathode.


Also in the GCSE/IGCSE/O level notes

There are detailed descriptions of simple electrolysis experiments

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

Chemical Equilibrium Notes Part 7 Index

TOP OF PAGE

KS3 BIOLOGY QUIZZES ~US grades 6-8 KS3 CHEMISTRY QUIZZES ~US grades 6-8 KS3 PHYSICS QUIZZES ~US grades 6-8 HOMEPAGE of Doc Brown's Science Website EMAIL Doc Brown's Science Website
GCSE 9-1 BIOLOGY NOTES GCSE 9-1 CHEMISTRY NOTES and QUIZZES GCSE 9-1 PHYSICS NOTES GCSE 9-1 SCIENCES syllabus-specification help links for biology chemistry physics courses IGCSE & O Level SCIENCES syllabus-specification help links for biology chemistry physics courses
Advanced A/AS Level ORGANIC Chemistry Revision Notes US K12 ~grades 11-12 Advanced A/AS Level INORGANIC Chemistry Revision Notes US K12 ~grades 11-12 Advanced A/AS Level PHYSICAL-THEORETICAL Chemistry Revision Notes US K12 ~grades 11-12 Advanced A/AS Level CHEMISTRY syllabus-specificatio HELP LINKS of my site Doc Brown's Travel Pictures
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.

Chemical Equilibrium Notes Part 7 Index

 Doc Brown's Chemistry 

*

best gift deals latest video game release, best gift deals best bargains in shop sales latest pop music releases, 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, best sales deals shoes, sweets and chocolates, magazines and make-up best gifts for teenagers Boys buy food and drink, computer games best gift deals best bargains in trainers shop sales DVDs and CDs, 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 shoes shop sales Girls spend a lot of money on clothes best gift deals color colour preferences in clothes, cool sunglasses best sales deals boys buy expensive thins like best gifts for teenagers designer sports clothes and trainers, teenagers save for holidays, best sales deals clothes, mobile phones, birthday presents and electronic goods, teenage accessories, Favourite style of jeans. best gifts for teenagers A typical girl’s shopping list includes mobile phone credit deals best shoes gift deals fashionable quality cool airpods, air pods, fashionable clothes best sales deals the most popular favourite sneakers best gifts for teenagers fancy shoes, sweets, chocolates, magazines, best trainers gift deals best bargains in shop sales lip moisturizer best bargains in  shop sale slots on make-up, well being, teenage decor decorating their room best sales deals teenagers like LED string lantern lights, best gifts for teenagers beauty products for teenagers, denim jackets, scrunchies coolness, fashionable back packs, 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, what teenagers talk about best gift deals what teenagers worry about, what teenagers like to do for fun sports best sales deals what cool things do teenagers buy, resale websites like eBay Teenager 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 high tech products latest fashion in trainers latest fashion in shoes latest fashion in mobile phones cell phones

TOP OF PAGE