5.3.1 Application of Redox Equilibria Flashcards
What is a redox reaction?
A reaction where electrons are transferred.
What is oxidation?
A loss of electrons.
What is reduction?
Gaining electrons.
What is the term for oxidation and reduction happening simultaneously?
Redox.
What is an oxidising agent?
Something that accepts electrons and is itself reduced.
What is a reducing agent?
Something that donates electrons and itself is oxidised.
How are atoms treated when calculating oxidation numbers?
As ions, even if they are covalently bonded.
What is the oxidation number of uncombined elements?
0
What is the oxidation number of elements bonded to identical atoms?
0
What is the oxidation number of simple monatomic ions?
The same as their charge.
What is the overall oxidation number of compound ions?
The ion charge.
What is the sum oxidation numbers for a neutral compound?
0
What is the oxidation number of combined oxygen?
-2 except in peroxides where it is -1 and in fluorides.
What is the oxidation number of combined hydrogen?
+1 except in metal hydrides where it’s -1.
What do the roman numerals in a chemical name represent?
Oxidation numbers.
What happens to the oxidation state of an atom when an electron is lost?
It increases by 1.
What happens to the oxidation state of an atom when an electron is gained?
It decreases by 1.
What is the name for when an element is oxidised and reduced at the same time?
Disproportionation.
What does an ionic half equation show?
Oxidation or reduction.
How can you make a full equation from ionic half equations?
Combine an oxidation half equation with a reduction half equation.
When combining ionic half equations, what must balance?
Electrons lost/gain and therefore oxidation number.
Give the ions half equation for zinc loses two electrons.
Zn(s) → Zn2+(aq) + 2e-
What happens to zinc in this equation?
Zn(s) → Zn2+(aq) + 2e-
Zinc is oxidised.
What happens to the oxidation number of zinc in this equation?
Zn(s) → Zn2+(aq) + 2e-
It increases by 2.
Balance these two ionic half equations:
Zn(s) → Zn2+(aq) + 2e-
Ag+(aq) + e- → Aq(s)
Zn(s) + 2Ag+(aq) → Zn2+(aq) + 2Ag(s)
How can you make a simple electrochemical cell?
Dip two different metals in salt solutions of their own ions and connect them with a wire and salt bridge.
What happens in a zinc/copper cell?
Zinc loses electrons (is oxidised) in the left cell, realising electrons into the external circuit. Electrons are taken from the external circuit by copper ions, reducing them to copper atoms.
Give an example of two ions of the same element that could be used to create an electrochemical cell.
Fe2+ and Fe3+
What are electrode potentials measured against?
A standard hydrogen electrode.
What is the standard electrode potential of a half-cell?
The voltage measured under standard conditions when the half-cell is connected to a standard hydrogen electrode.
What is a standard hydrogen electrode?
Platinum foil submerged in 1mol dm^-3 of H+ ions (acid) with H2 gas bubbled through at 101kPa.
Why is the platinum electrode platinized?
To increase its surface area.