1.7 Redox
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What is oxidation?
The loss of electrons. The gain of oxygen.
What is reduction?
The gain of electrons. The loss of oxygen.
What is a redox reaction?
When a species is reduced and another species is oxidised in the same reaction.
How do you formulate a half equation?
• Separate the ionic equation into the half equations. • Balance both sides of the half equation with atoms. • Add water to balance any oxygens. • Add H⁺ to balance any hydrogens. (from the addition of 3. water) • Add electrons so the charges on both sides of the equation are balanced. • Recombine both equations. (if alkaline conditions add OH¯ to balance any excess H⁺)
Whats the acronym to follow to make half equations?
Separate Atoms Water Hydrogens Electrons Recombine (SAWHER)
What is the oxidation state of an uncombined element?
0
What is the oxidation state of H?
+1
When is the oxidation state of H, -1?
In metal hydrides (ie NaH)
What is the oxidation state of group 1 metals?
+1
What is the oxidation state of group 2 metals?
+2
What is the oxidation state of Al?
+3
What is the oxidation state of O?
-2
What are the exceptions to the oxidation state of O?
-1 in peroxides +2 in OF₂
What is the oxidation state of F?
-1
What is the oxidation state of Cl?
-1
What is the exception to the oxidation state of Cl?
+ve when in compounds of O/F
What is the oxidation state when an element has been reduced to an ion?
-ve
What is the oxidation state when an element has been oxidised to an ion?
+ve
What is the oxidation state of the most electronegative element in a compound/reaction?
Always -ve