Unit 5: Oxidation and Reduction Flashcards
(41 cards)
What was oxidation and reduction initially referred to?
Oxidation - An element combining with oxygen to produce an oxide.
Reduction - A substance losing oxygen
What is oxidation and reduction?
Oxidation - Losing electrons
Reduction - Gaining electrons
What are oxidizing agents and reducing agents?
Oxidizing agents - gain electrons (take them)
Reducing agents - lose electrons (give them)
What are net and total ionic equations?
Total - Break apart aqueous substances into ions
Net - Remove spectator ions.
Redox of moleculars compounds
Molecular compounds are not ionic, they share electrons. This unequal sharing determines what is oxidized and reduced (use the electronegativity values).
Ex: H2 + O2 -> H2O, Oxygen is more electronegative that hydrogen, so the oxygen holds electrons more often, and is reduced (partially gains electrons).
What is a half reaction?
Balanced to have an equal number of electrons.
Ex. S + 2e- -> S^-2
How do you tell whether a reaction is spontaneous or not?
If the oxidizing agent is higher than the reducing agent on a table of reduction half reactions, then it is spontaneous. And vice versa.
What the the word corrosion from?
Latin: to gnaw
When does corrosion usually occur?
When water is in contact with the metal in the presence of oxygen.
What can corrosion cause?
Things to become stuck.
Holes in metal.
Poor conductors.
Lost magnetic ability.
Weaker metals.
How can corrosion be prevented? How?
Painting/coating: prevents water and oxygen from contacting metal. Oil and grease can help as well.
Galvanizing: coat in zinc, prevents contact and sacrificial metal.
Sacrificial metal: More reactive metal is placed in the vicinity of the metal that needs corrosion protection. Does not necessarily need to coat metal.
Alloys: Can have better properties, such as not rusting, or using a s as ridiculous metal (like nickel and chromium).
Cathodic protection: sacrificial metal connected via electric current that transfers electrons.
What is an alloy?
A metal combined with another substance to create new properties.
Oxidation number of a free uncombined element?
0
Oxidation number of oxygen combined with something else?
-2
Total of all oxidation numbers in a compound?
0
Oxidation number of monatomic ion?
Equal to charge, ex: Fe(III) = +3
Oxidation number of H combined with something else?
+1, aside from metal hydrides, in which case -1.
How do you balance with oxidation numbers?
Assign numbers
Identify what is oxidized and reduced
Write change in oxidation number by square brackets
Multiply to make changes equal
Put coefficients in front
Check overall balance and make changes
What reactions normally are redox, aren’t, or sometimes are?
Usually: combustion and single displacement
Not: neutralization and double displacement
Sometimes: synthesis and decomposition
What are the characteristics of redox reactions?
Either oxygen atoms, hydrogen atoms, or electrons are transferred.
Both oxidation and reduction must be present.
Reciprocity: If you took the reverse reaction of oxidation, the result would be reduction, and vice versa.
What is patina?
A layer of oxide formed on the surface of metal
Why doesn’t copper rust away like iron?
Iron flakes and peels when it rusts, exposing more iron.
Copper leaves a layer of oxide on the surface that protects the rest.
Oil rig acronym.
Oxidation Is Loss (of electrons)
Reduction Is Gain (of electrons)
What are the six types of chemical reactions?
Synthesis, single displacement, double displacement, decomposition, combustion, neutralization.