M2 - Redox
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Explain (using examples) when the oxidation number is zero?
For elements on their own (e.g. Na, K & Fe) or bonded to atoms of the same element (e.g. H2, N2 & Br2)
What is the oxidation number of Oxygen in a compound generally?
-2 (except in peroxides such as H2O2, where the oxidation no. of O is -1)
What is the oxidation number of Hydrogen in a compound generally?
+1 (except in metal hydrides such as NaH or CaH2, where the oxidation no. of H is -1)
What is the oxidation number of Fluorine in a compound generally?
-1
What is the common oxidation number of Na or K in a compound?
+1
What is the common oxidation number of Mg or Ca in a compound?
+2
What is the common oxidation number of Halides in a compound?
-1
Provide an example for when oxygen can have an oxidation number of +2?
In the compound F2O
In ions, what must the overall oxidation number be equal to?
The sum of the oxidation numbers is equal to the total charge, e.g. SO4 2- (S = +6 & O = -2 x 4)
What do roman numerals mean in the use of iron(II) chloride or iron(III) chloride?
Iron(II) represents Fe2+ with oxidation number +2 Iron(III) represents Fe3+ with oxidation number +3
What is the systematic name for TiCl4?
Titanium(IV) chloride
What is the systematic name for Fe2O3?
Iron(III) oxide
What is the formula for Bromate(V)?
BrO3-
What is the formula for Dichromate(VI)?
Cr2O72-
What is oxidation in terms of electron transfer & oxidation number?
The loss of electrons / increase in oxidation number
What is reduction in terms of electron transfer & oxidation number?
The gain of electrons / decrease in oxidation number
Mg + CuSO4 → Cu + MgSO4 Explain, in terms of numbers of electron transferred, the redox processes taking place in this reaction [2].
Magnesium (atoms) has been oxidised AND Because it has lost two electrons ✓ Copper (ions) has been reduced AND Because it has gained two electrons ✓
3Mg + 2H3PO4 → Mg3 (PO4)2 + 3H2 In terms of the number of electrons transferred, explain whether magnesium is being oxidised or reduced [1].
Oxidised AND (Mg) transfers/loses/donates 2 electrons✓
MnO2 + 4HCl → MnCl2 + 2H2O + Cl2 Using oxidation numbers, show what has been oxidised and what has been reduced in this reaction [2].
Cl (has been oxidised) from Cl = –1 to Cl = 0 ✔ Mn (has been reduced) from Mn = +4 to Mn = +2 ✔
What is meant by the term disproportionation? [1]
Oxidation and reduction of the same element ✓
2Cl2 + 2Ca(OH)2 → CaCl2 + Ca(OCl)2 + 2H2O This is a disproportionation reaction. State what is meant by disproportionation and use oxidation numbers to show that disproportionation has taken place [3].
Oxidation AND reduction of same element/chlorine OR Chlorine/Cl has been oxidised AND chlorine/Cl has been reduced ✓ Oxidation from 0 in Cl2 to +1 in Ca(OCl)2 OR ClO- ✓ Reduction from 0 in Cl2 to –1 in CaCl2 OR Cl- ✓
A
D
B