Oxidation and Reduction Flashcards
What is oxidation?
The addition of oxygen, the loss of electrons and the increase in oxidation number
What is reduction?
A loss of oxygen, gain of electrons and decrease in oxidation number
What does an oxidising agent do?
causes oxidation and is itself reduced
What does a reducing agent do?
causes reduction and is itself oxidised
What is the most abundant element on the earths crust and in the human body?
Oxygen
What does oxygen combine with?
the vast majority of other elements
What is oxygen involved in?
some of the most important chemical reactions - burning, respiration, rusting
What did oxidation used to be defined as and give an example?
the addition of oxygen to a substance e.g. C + O2 -> CO2
What did reduction used to be defined as?
the removal of oxygen
Before the discovery of electrons, what were reactions that involved the addition of oxygen to a substance described as?
oxidation reactions
What was removing oxygen from a substance previously described as? Why?
a reduction reaction as the mass to the substance got smaller due to the oxygen being removed
What did scientists notice after the discovery of the electron?
Scientists examined reactions more closely and noticed that many chemical reactions involved the transfer of electrons. One substance lost electrons while another gained electrons.
What did the transfer of electrons involve?
One substance losing electrons while another gained electrons.
What is oxidation?
When an element loses electrons
What is reduction?
Reduction is when an element gains electrons
What do we use to remember oxidation and reduction?
OIL RIG
What does OIL RIG stand for?
Oxidation Is Loss, Reduction Is Gain
Write down a formula to show oxidation and reduction explaining what has been oxidised and why
Zn + Cu2+ -> Zn2+ + Cu (remember Zn is more positive so it lost negatives so it has been OXIDISED not REDUCED)
When do oxidation and reduction occur?
At the same time
If one element loses electrons, what happens to another element?
It gains electrons
Give two examples of REDOX reactions
- MgO -> Mg2+ + O2-
2. Zn + Cu2+ -> Zn2+ + Cu
Give an example of a REDOX reaction and explain
MgO -> Mg2+ + O2-
In the above example we can see that the Mg atom loses 2e to become the Mg2+ ion. The O atom gains 2e to become the O2- ion.
Name the metals more reactive than hydrogen from most reactive to least reactive
Potassium (K), Sodium (Na), Calcium (Ca), Magnesium (Mg), Aluminium (Al), Zinc (Zn), Iron (Fe), Tin (Sn), Lead (Pb) and then |Hydrogen| |H|
Name the metals less reactive than hydrogen from most reactive to least reactive
Copper (Cu), Mercury (Hg), Silver (Ag), Gold (Au)
What is electrolysis?
The use of electricity to bring about a chemical reaction in an electrolyte
What is an electrolyte?
An electrolyte is a compound which when molten or dissolved in water will conduct an electric current
What is the conduction of electricity due to?
the presence of ions
What is the electrochemical series?
a list of elements in order of their standard electrode potential (reactivity - how easily they lose electrons)
What are electrodes?
The two rods that dip into the electrolyte and make electrical contact with it
What are the two types of electrodes?
Inert (do not react with electrolyte) and Active (react with electrode)
What are examples of inert and active?
inert -> graphite and platinum
active -> copper and iron
how is the electrochemical series organised?
top of the list readily lose electrons
bottom = unreactive
are the electrodes positive or negative?
One electrode is positive and the other is negative
is a cathode negative or positive?
negative
is an anode positive or negative?
positive
how do we remember the charge of cathodes and anodes?
CNAP
What does CNAP stand for?
Cathode, Negative, Anode, Postive
What happens to electrons in the electrodes?
The battery “pumps” electrons to the negative electrode where they are gained by some species and carried to the positive electrode where they are lost
oxidation at anode or cathode?
anode
reduction at anode or cathode?
cathode
What happens in electrodes connected to a DC current?
Positive ions move to negative electrode and gain electrons
Negative ions move to positive electrode and lose electrons
anion positive or negative?
negative
cation positive or negative?
positive
Write the equations for when an electrical current passes through a solution of potassium iodide using inert electrodes.
Anode (+): 2I- -> I2 + 2e-
(loss of electrons - oxidation)
Cathode (-): 2H2O + 2e- -> H2 + 2OH-
(gain of electrons - reduction)
Do K+ ions gain electrons at cathode?
no
does K+ + e- -> K takes a lot of energy?
yes
is K+ a spectator ion?
yes
