Oxidation is a reactionwhere oxygencombines with anelement/compound toform anothersubstance
Oxidation – Gain of oxygenWhen calcium burns in oxygen, the followingreaction takes placecalcium + oxygen calcium oxide2Ca(s) + O2 2CaO(s)Since calcium has gained oxygen. It has beoxidised. Hence this is oxidation.
Oxidation – Loss of HydrogenWhen 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 beenoxidised.
Oxidation – Loss of ElectronsOxidation can still take place despite having nooxygen/hydrogen. When a substance loseselectrons 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 OxygenWhen zinc burns in copper(II) oxide, thefollowing 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 HydrogenWhen nitrogen burns with hydrogen gas, thefollowing reaction takes place.Nitrogen +Hydrogen AmmoniaN2 + 3H2 2NH3Nitrogen gain hydrogen, thus it is being reduced.
Reduction-Gain Of Electron When iron reacts with chloride acid, thefollowing reaction takes place.Iron + chlorine Iron(III) + Chloride2Fe2++Cl2 2Fe3++2Cl-Since iron loses electron, it is oxidised. Chlorinegains 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)
The oxidation state is thecharge an atom of anelement would have if itexisted as an ion in acompound.
To work out the oxidation state of an atom, we apply the following rules:Rule Example Oxidation state1. The oxidation state of a Cu, S, Cl2 0, 0, 0free element is zero.2. The oxidation state of a K+, Zn2+, Cl-, O2- +1, +2, -1, -2simple ion is the same asthe charge on the ion.3. The oxidation states of Ca, C, 3O +2, +4, 3x(-2)=-6the atoms present in theformula of a compound All add up to zero.add up to zero. Theexample shown here isCaCO3 .4. The total of the S, 4O +6, 4x(-2)=-6oxidation states of theatoms in a polyatomic ion All add up to -2.is equal to the charge onthe ion. The exampleshown here is SO4 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.