Strength of acidsWHAT CONTROLS THE STRENGTH OFAN ACID?An energy cycle helps us focus on the two key ideas that help usanswer this question:H+A-1. How easy is it toBreaking thebondHydratingbreak the bondEtheionsH-Ajoining the hydrogento the rest of the acidparticle? If the bondAcidstrengthBond strengthis weak, then the5.62×104562kjmol-1千Facid is likely to be431klmol-11×107F-CIstrong.1×109366klmol-1H-Br1×1011299klmol-12. How stable is theanion formed? If theSO 2- (sulfate ion) is a more stable anionanion is stable, thethan SO,2- (sulfite ion).acid is likely to beThis is why H,SO4 (sulfuric acid) is a,strong.stronger acid than H,SO, (sulfurous acid)
11 Strength of acids WHAT CONTROLS THE STRENGTH OF AN ACID? An energy cycle helps us focus on the two key ideas that help us answer this question: 2. How stable is the anion formed? If the anion is stable, the acid is likely to be strong. 1. How easy is it to break the bond joining the hydrogen to the rest of the acid particle? If the bond is weak, then the acid is likely to be strong. SO4 2- (sulfate ion) is a more stable anion than SO3 2- (sulfite ion). This is why H2SO4 (sulfuric acid) is a stronger acid than H2SO3 (sulfurous acid)
Strength of acidsWordsWords and Expressionsprotonate:proton;protonationacid; acidity; base (alkali); basicity; alkalinebench:bench-scale;pilot-plant-scale;production12
12 Strength of acids Words protonate: proton; protonation acid; acidity; base (alkali); basicity; alkaline bench: bench-scale; pilot-plant-scale; production Words and Expressions
Buffer solutionBuffer solutionsS resist changes in pH on addition of acid oralkaliBuffer solutions tend to resist changes in pH when small amountsof acid or base are added and their pHis not affected by dilutionAcidic buffers are made of a solution of a weak acid and itsconjugate base, e.g. a solution of ethanoic acid and sodiumethanoate.Basic buffers are made of a solution of a weak base anditsconjugate acid, e.g. a solution of ammonia and ammoniumchloride.13
13 Buffer solution Buffer solutions tend to resist changes in pH when small amounts of acid or base are added and their pH is not affected by dilution. Acidic buffers are made of a solution of a weak acid and its conjugate base, e.g. a solution of ethanoic acid and sodium ethanoate. Basic buffers are made of a solution of a weak base and its conjugate acid, e.g. a solution of ammonia and ammonium chloride. Buffer solutions resist changes in pH on addition of acid or alkali
Redox reactionsRedox reactionsReduction and oxidation reactions involve the transfer or lossand gain of electrons.ACID-BASE ANDREDOXAcid-base reactions involveRedox reactions involve electronproton transfer. Becausetransfer. Because electrons do notprotons are written as Hit isappear in most written equations.usually easy to see whichitis notalways obviouswhichhasparticle has lost a protonlost or gained electrons. But it isand which has gained one.not hard to work this out.H,O+HCI → H,O++CI-S0,+2H,S → 3S+2H,0↑oxidized orgains a protonlostor gainedreduced?losesaproton14electrons?
14 Redox reactions Redox reactions Reduction and oxidation reactions involve the transfer or loss and gain of electrons. Acid-base reactions involve proton transfer. Because protons are written as H it is usually easy to see which particle has lost a proton and which has gained one. H2O + HCl → H3O+ + Cl－ ACID-BASE AND REDOX Redox reactions involve electron transfer. Because electrons do not appear in most written equations, it is not always obvious which has lost or gained electrons. But it is not hard to work this out. SO2+2H2 S → 3S+2H2O gains a proton loses a proton oxidized or reduced? lost or gained electrons?
Redox reactionsOxidationOxidation is defined as the loss of electronsReductionReduction is defined as the gain of electronsRemember ‘OIL RIG'!Oxidation is loss: reduction is gain15
15 Redox reactions Oxidation Oxidation is defined as the loss of electrons Reduction Reduction is defined as the gain of electrons Remember ‘OIL RIG’! Oxidation is loss: reduction is gain