Back to the full dot-point answer

VICChemistryQuick questions

Unit 2: How do chemical reactions shape the natural world?

Quick questions on Redox reactions and oxidation numbers in water: VCE Chemistry Unit 2

12short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.

What is oxidation numbers (rules)?
Show answer
The oxidation number (or oxidation state) is the hypothetical charge an atom would have if every bond were ionic. Use the rules in order; later rules yield to earlier ones if there is a conflict.
What is oxidation and reduction?
Show answer
Oxidation is loss of electrons; the oxidation number increases. Reduction is gain of electrons; the oxidation number decreases.
What is balancing half-equations in acidic solution?
Show answer
A half-equation is a balanced equation showing one half of the redox reaction with electrons explicitly. Use this procedure for acidic solution:
What is combining half-equations?
Show answer
1. Multiply each half by the appropriate factor so the electrons cancel (find the LCM of the electrons in each half). 2. Add the two halves.
What is half 1?
Show answer
derived above. MnO4^- + 8H^+ + 5e^- -> Mn^2+ + 4H2O
What is half 2?
Show answer
S balanced. O: add H2O on left (1 O needed): SO3^2- + H2O -> SO4^2-. H: add 2 H^+ on right: SO3^2- + H2O -> SO4^2- + 2H^+.
What is forgetting to include H2O and H^+?
Show answer
In acidic solution they are part of the half-equation and must appear if O or H balances require them.
What is balancing in basic solution by accident?
Show answer
This dot point is acidic solution only. Adding OH^- to your half-equation in this course will lose marks.
What is putting electrons on the wrong side?
Show answer
Oxidation produces electrons (e^- on the right). Reduction consumes electrons (e^- on the left).
What is forgetting to cancel H^+ and H2O when adding halves?
Show answer
The overall equation should not contain electrons, and the H^+/H2O on the same side should be combined and simplified.
What is reading too much into "oxidation"?
Show answer
"Oxidised" means lost electrons; it does not require oxygen as a reactant (Zn -> Zn^2+ + 2e^- is oxidation despite no oxygen anywhere).
What is calling the substance reduced "the reductant"?
Show answer
The oxidant is reduced; the reductant is oxidised. Practise saying both pairs out loud.

All ChemistryQ&A pages