2.1.5 - Redox
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What is an oxidation number?
The number of electrons an atom uses to bond with any other atom
What is the oxidation number of an uncombined element such as C, H, O2?
0
What is the oxidation number of combined oxygen such as in H2O?
-2
What is the oxidation number of oxygen in peroxides?
-1
What is the oxidation number of combined hydrogen such as in NH3, H2S?
+1
What is the oxidation number of combined hydrogen in metal hydrides such as LiH?
-1
What is the oxidation number of a simple ion?
Charge on the ion e.g. Na+ ——-> +1 Cl- ————> -1
What is the oxidation number of combined fluorine such as NaF, CaF2?
-1
When an element has more than one stable oxidation number, how is it indicated?
Written as a Roman numeral
What is the oxidation number of Fe in Iron (lll) chloride
+3
What are oxyanions?
Negative ions that have an element along with oxygen
What is the oxidation number of S in SO4^2-?
+6 Because combined oxygen has an oxidation number of -2 4 x -2 = -8 The charge on the compound is -2. Sum of oxidation number must be equal to -2 So -2 - (-8) = +6
Define oxidation in terms of electron transfer and oxidation number
Oxidation is • loss of electrons • An increase in oxidation number
Define reduction in terms of electron transfer and oxidation number
Reduction is • Gain of electrons • A decrease in oxidation number
What is a redox reaction?
A reaction in which both oxidation and reduction takes place
What is the oxidation number of a metal?
0, because it is an uncombined element