Topic 9.1: Oxidation and reduction Flashcards
What is transfered between atoms during REDOX reactions?
Electrons
Main features of an oxidation reaction
a) Loss of electrons
b) Loss of hydrogen
c) Gain of oxygen
Main features of an reduction reaction
a) Gain of electrons
b) Gain of hydrogen
c) Loss of oxygen
Oxidation state (number)
Measure of the e- control of an atom in a compound relative to its pure element
Representation of:
a) Oxidation state
b) Oxidation number
a) Roman number (Copper (I) oxide)
b) Sing + Number (+1)
What does an increase and decrease in oxidation number mean?
a) An increase means oxidation
b) A decrease means reduction
Rules for assigning oxidation states
a) Sum of oxidation state for a neutral compound = 0
b) Element by itself = 0
c) Monoatomic ion = Ion charge
d) Halogens = Usually /1 (+1 with oxygen)
e) Oxygen = -2 (-1 in peroxide)
f) Sum of oxidation state for a polyatomic ion = Ion charge
g) Group 1/2/3 = Always +1/+2/+3
h) Hydrogen = +1 (-1 with metals)
j) Fluorine = Always -1
What is the main feature of the oxidation state of d-block elements and most main group non-metals?
Variable oxidation states
Function of oxidizing and reducing agent
a) Makes oxidation happen, so the agent must take the electrons from the substance
b) Makes reduction happen, so the agent must give an electron to the substance
IUPAC Nomenclature of a transition metal compound
A Roman numeral corresponding to the oxidation state is inserted in brackets after the name of the element
Activity series
Arranging metals based on their relative reactivity and their strength as reducing agents
What are the main features of metals at the top of the activity series?
Metals are more reactive and stronger reducing agents (more readily oxidized)
What are the main features of metals at the bottom of the activity series?
Metals are less reactive and weaker reducing agents (less readily oxidized)
What is the relationship between the difference in reactivity of two metals and time for single displacement reactions?
The greater the difference in reactivity of two metals, the more rapidly the reaction would occur
When can a metal only displace another in a compound?
a) If it is higher in the activity series
b) More reactive elements will replace less reactive elements in a compound
Analysis of Fe with MnO4-
a) In REDOX titration, Fe2+ is oxidized to Fe3+ by an oxidizing agent
b) The oxidizing agent is usually acidified KMnO4
Iodine thiosulfate reaction
a) An oxidizing is used to react with excess iodide ions to form iodine
b) The liberated iodine, I2, is then titrated with sodium thiosulfate, Na2S2O3
Biochemical oxygen demand (BOD) definition
The amount of O2 used by the aerobic microorganisms in H2O to decompose the organic matter in H2O over a fixed period of time
Dissolved oxygen and levels of pollution
As the level of pollution in H2O increases, the dissolved O2 content decreases as the O2 is used by bacteria in decomposition reactions.
Winkler method
Measure the concentration of dissolved oxygen in water
Main ratio of O2 to S2O3 2-
1:4 as one mole of O2 reacts with 4 mols of S2O3 2-
