Tag Archives: cells

Chapter 27/28: Six Universal Principles of Redox Reactions

Redox can be a confusing topic for VCE Chemistry students. It’s also taught right at the end of the year, when students are tired and some teachers are rushing their lessons so they can finish the course before the end of Term 3. Student motivation levels are at their lowest time of the year, which means that students often finish the course with an incomplete understanding of Redox.

Fortunately, there are six universal principles that are always true in Redox no matter what type of cell is being studied.

First, here’s a reminder of the types of cells you need to have studied in this course.

Galvanic Cells

  • Primary (can’t be recharged)
  • Secondary (can be recharged)
  • Fuel Cells (reactants are supplied continuously)

Electrolytic Cells

  • Electroplating Cells (no overall reaction)
  • Electrolytic Cells (non-spontaneous reaction)
  • Commercial Cells (usually molten electrolytes)
  • Recharge reaction of a secondary cell (non-spontaneous)

Now, here are the six universal Redox principles.

1. The strongest oxidant at the cathode reacts with the strongest reductant at the anode (SOC SRA)

To predict which species will react with each other, circle all the species present at the cathode on the electrochemical series. The highest species on the left will always react. Now, circle all the species present at the anode… the lowest species on the right will react.

2. The half-reaction with the highest E° value is always positive

In all cells, the half-equation with the highest electrode potential (also called ‘reduction potential’ or E° value) always occurs at the positive electrode. Similarly, the half-equation with the lowest electrode potential (E°) will always occurs at the negative electrode.


Oxidation is loss of electrons. Reduction is gain of electrons.


Anode reaction (oxidation reaction) is whichever reaction is happening to the left in the electrochemical series.

Cathode reaction (reduction reaction) is whichever reaction is happening to the right in the electrochemical series.

5. Electrons always flow in this order (RACO)

Reductant → anode → cathode → oxidant

6. In the internal circuit, cations always flow to the cathode, and anions always flow to the anode.

The internal circuit might be an electrolyte or a salt bridge that contains soluble weak oxidants and reductants such as KNO3(aq) (potassium nitrate). Either way:

  • cations always flow to the cathode; and
  • anions always flow to the anode.

Keep practicing redox questions by completing past papers, Checkpoints and Lisachem questions. If you need more help, contact me via the Get a Tutor button in the site’s menu bar. Students learn much faster with a tutor than on their own.

For more Study Tools for Year 12 students, click here.

Image courtesy of Annenberg Learner

Book: Molecular Biology of the Cell (Alberts’)

Molecular Biology of the Cell
Each edition changes colour. Fifth edition is red. Fourth edition is grey.

The KitchenAid of biology. All other biology textbooks are just accessories.
1392 pages, ★★★★★

Molecular Biology of the Cell, or “Alberts'”, as it’s known colloquially, is the cornerstone of a university education in biology. All biology undergraduates will have seen it, most of them will buy it, yet none of them will actually read it. They should.

Alberts’ details every aspect of cell biology, and delves deeply into physiology, neurology and pharmacology as well—rendering some undergraduate textbooks in those fields redundant.

Illustrations are crisp, clear and never excessive. Colour is used for clarity but not for aesthetics. The text is prose-heavy and reads like a story so it can be read cover-to-cover quite comfortably (albeit slowly). And that’s exactly what students should do.

Many students will use Alberts when they need to learn about something quickly, such as, “what shape is a mitochondria?”, “what does kinesin do?”, or “in what order does the electron transfer chain take place?” If you haven’t read this book from cover-to-cover already, then finding those answers is going to take much longer than you think. Alberts is not a reference book—it’s a comprehensive background story. Quick answers can be found on Google, but genuine understanding comes from a cover-to-cover reading of Alberts. ★★★★★