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Redox Reaction
Oxidation is a reaction where oxygen combines with an element/compound to form another substance
Oxidation – Gain of oxygen
When calcium burns in oxygen, the following reaction takes placecalcium + oxygen calcium oxide2Ca(s) + O2 2CaO(s)
Since calcium has gained oxygen. It has be oxidised. Hence this is oxidation.
Oxidation – Loss of Hydrogen
When ammonia is passed over heated copper(II) oxide, the following reaction takes place.
ammonia + copper(II) oxide nitrogen + copper + water vapour2NH3(g) + 3CuO(s) N2(g) + 3Cu(s) + 3H2O(g)
Since ammonia has lost hydrogen, it has been oxidised.
Oxidation – Loss of Electrons
Oxidation can still take place despite having no oxygen/hydrogen. When a substance loses electrons it is considered oxidation.
magnesium + chlorine magnesium chlorideMg(s) + Cl2(g) MgCl2(s)
What is Reduction?
Definition Of Reduction
• Reduction is a chemical reaction where it loses oxygen, gain hydrogen, gain electron and have a decrease in oxidation state by a molecule, atom or ion.
• A reactant that reduces another substance is a reducing agent.
• The reducing agent transfers electrons to another substance, it reduces others, and is thus itself oxidized. And, because it "donates" electrons, it is also called an electron donor.
Reduction-Loss Of Oxygen
When zinc burns in copper(II) oxide, the following reaction takes place.Zinc + copper oxide Zinc oxide + copperZn(s)+CuO(s) ZnO(s)+Cu(s)
Since Zinc has gain oxygen,it is oxidised. Copper(II) oxide loses oxygen,thus it is reduced.
Reduction-Gain Of Hydrogen
When nitrogen burns with hydrogen gas, the following reaction takes place.Nitrogen +Hydrogen AmmoniaN2 + 3H2 2NH3
Nitrogen gain hydrogen, thus it is being reduced.
Reduction-Gain Of Electron
When iron reacts with chloride acid, the following reaction takes place.Iron + chlorine Iron(III) + Chloride2Fe2++Cl2 2Fe3++2Cl-
Since iron loses electron, it is oxidised. Chlorine gains electron, thus it is reduced.
Common Reducing Agent
• Lithium aluminium hydride (LiAlH4)• Nascent (atomic) hydrogen• Sodium amalgam• Diborane• Sodium borohydride (NaBH4)• Compounds containing the Sn2+ ion, such as tin(II) chloride• Sulfite compounds• Hydrazine (Wolff-Kishner reduction)• Zinc-mercury amalgam (Zn(Hg)) (Clemmensen reduction)• Diisobutylaluminum hydride (DIBAL-H)• Lindlar catalyst• Oxalic acid (C2H2O4)• Formic acid (HCOOH)• Ascorbic acid (C6H8O6)• Phosphites, hypophosphites, and phosphorous acid• Dithiothreitol (DTT) – used in biochemistry labs to avoid S-S bonds• Compounds containing the Fe2+ ion, such as iron(II) sulfate• Carbon monoxide(CO)• Carbon (C)
Oxidation State
The oxidation state is the charge an atom of an element would have if it existed as an ion in a compound.
To work out the oxidation state of an atom, we apply the following rules:
Rule Example Oxidation state
1. The oxidation state of a free element is zero.
Cu, S, Cl2 0, 0, 0
2. The oxidation state of a simple ion is the same as the charge on the ion.
K+, Zn2+, Cl-, O2- +1, +2, -1, -2
3. The oxidation states of the atoms present in the formula of a compound add up to zero. The example shown here is CaCO3 .
Ca, C, 3O +2, +4, 3x(-2)=-6
All add up to zero.
4. The total of the oxidation states of the atoms in a polyatomic ion is equal to the charge on the ion. The example shown here is SO4 2- .
S, 4O +6, 4x(-2)=-6
All add up to -2.
Solution to question: Find the oxidation state of each element in ammonium sulfate.
(NH4)2SO4Since hydrogen in NH4 has an o.s of +1,Ammonium has a charge of 1.Let n be x2(x+4(1))=22x-2-8x=-3Hence nitrogen has an o.s of -3
Since oxygen in SO4 has an o.s of -2,Sulfate has a charge of -2.Let s be yy+4(-2)=-2y-8=-2y=6Hence sulfur has an o.s of 6.
Source
CHEMISTRY Matters textbook
Done by
• Edwin• Kian Leong• Jeremy• Melvan