acids and bases. acids definition : latin meaning sour “acidus” lots of acids –dangerous...

Acids and BasesAcids and Bases

AcidsAcids

Definition : latin meaning sour “Acidus”Definition : latin meaning sour “Acidus”

Lots of acidsLots of acids– DangerousDangerous

Nitric Acid, Sulfuric Acid Nitric Acid, Sulfuric Acid – EssentialEssential

Ascorbic AcidAscorbic Acid– DietaryDietary

Acetic Acid (ethanoic acid) (vinegar), Citric Acid, Carbonic Acetic Acid (ethanoic acid) (vinegar), Citric Acid, Carbonic AcidAcid

– OddOddStearic Acid, Benzoic AcidStearic Acid, Benzoic Acid

infoinfo

Turns blue Litmus paper RedTurns blue Litmus paper Red

React with metals to produce hydrogen React with metals to produce hydrogen gasgasHH22SOSO44 + Zn + Zn ZnSOZnSO44 + H + H22

React with Carbonates to produce COReact with Carbonates to produce CO22

Arrhenius TheoryArrhenius Theory

An acid is a substance An acid is a substance that dissociates in that dissociates in water to produce Hwater to produce H++ ionsions– Svante Arrhenius (nobel prize 1903)Svante Arrhenius (nobel prize 1903)

Add HCl to water and we get HAdd HCl to water and we get H++ ions and ions and Chlorine Chlorine

Nitric and Sulfuric acid behave the sameNitric and Sulfuric acid behave the same

HClHCl HH++ ++ ClCl

HNOHNO33 HH++ ++ NONO33

HH22SOSO44 2H2H++ ++ SOSO442-2-

When we add a solution of Hydrogen chloride When we add a solution of Hydrogen chloride to water we call it to water we call it HydrochlHydrochlooric acidric acid

Mono basic: Mono basic: HClHCl HH++ ++ ClCl

Di BasicDi Basic H H22SOSO44 2H2H++ ++ SOSO442-2-

Tri Basic Tri Basic HH33POPO44 3H3H++ ++ POPO443-3-

Dependant on the number of hydrogen ions Dependant on the number of hydrogen ions donateddonated

Strong and weak acidsStrong and weak acids

Sulfuric and nitric are Sulfuric and nitric are strong as they dissociate strong as they dissociate fully in water but acetic fully in water but acetic acid is weak as it only acid is weak as it only partially dissociatespartially dissociates

Hydronium IonHydronium Ion

The HThe H++ ion ....just a proton ion ....just a proton

Cannot exist independently in solution so Cannot exist independently in solution so the Hydronium ion is bornthe Hydronium ion is born

The oxygen atom allows an electron to The oxygen atom allows an electron to form a dative covalent bond with the form a dative covalent bond with the hydrogen atomhydrogen atom

Hydrogen ion reacts with water toHydrogen ion reacts with water to

form Hydronium Ion Hform Hydronium Ion H33OO++

O

HX

H+

XH

.... ..HX

H+

XH

..O

.... +

Hydronium IonHydronium Ion

For accuracy we should useFor accuracy we should use

HA +HA + HH22OO HH33OO + + + + AA--

HCl +HCl + HH22OO HH33OO + + + + ClCl--

Many chemists simply say the hydrogen ionMany chemists simply say the hydrogen ion

Importance of waterImportance of water

If we add pure Hydrogen Chloride or If we add pure Hydrogen Chloride or acetic acid into a solvent like benzene (no acetic acid into a solvent like benzene (no water) we do not get either Hwater) we do not get either H++ or or Hydronium ion formation and blue litmus Hydronium ion formation and blue litmus paper stays bluepaper stays blue

Shows that Hydrogen Chloride or acetic Shows that Hydrogen Chloride or acetic acid is only acid when water is presentacid is only acid when water is present

BasesBases

Behave in the opposite manner to acidsBehave in the opposite manner to acids

Turn Red litmus paper blueTurn Red litmus paper blue

Example:Example:– Sodium Hydroxide (NaOH)Sodium Hydroxide (NaOH)

– Magnesium Hydroxide ([Mg(OH)Magnesium Hydroxide ([Mg(OH)22])])

– Calcium Hydroxide ([Ca(OH)Calcium Hydroxide ([Ca(OH)22])])

InfoInfo

Many bases have a soapy feelMany bases have a soapy feel

Used as degreasers in household Used as degreasers in household detergentsdetergents

Act by converting the oil into soap Act by converting the oil into soap which washes away more easilywhich washes away more easily


A base is a substance that dissociates in A base is a substance that dissociates in water to produce OHwater to produce OH-- ions ions

The OHThe OH-- ion is called the hydroxide ion ion is called the hydroxide ion

When added to water it dissociates When added to water it dissociates completely into Sodium ions and completely into Sodium ions and hydroxide ionshydroxide ions

NaOH NaOH NaNa++ ++ OH OH--


Similarly for Magnesium Hydroxide and Similarly for Magnesium Hydroxide and Calcium HydroxideCalcium Hydroxide

[Mg(OH)[Mg(OH)22]] MgMg2+2+ ++ 2OH 2OH--

[Ca(OH)[Ca(OH)22]] CaCa2+2+ ++ 2OH 2OH--

Strong and Weak basesStrong and Weak bases

Strong bases include Sodium Strong bases include Sodium Hydroxide because they Hydroxide because they dissociate almost completely in dissociate almost completely in water but ....Magnesium water but ....Magnesium Hydroxide and Calcium Hydroxide Hydroxide and Calcium Hydroxide do not and are referred to as do not and are referred to as weak basesweak bases

A number of flaws to the Arrhenius A number of flaws to the Arrhenius TheoryTheory

Hydronium ions are present not bare Hydronium ions are present not bare hydrogen ionshydrogen ions

Arrhenius theory limited to aqueous Arrhenius theory limited to aqueous solutions and not all acid base reactions solutions and not all acid base reactions are water basedare water based

NHNH33 ++ HClHCl NHNH44ClCl

BaseBase acidacid ammonium ammonium chloridechloride

Brønsted -LowryBrønsted -Lowry

Update needed to reflect more Update needed to reflect more accurately the reactions that accurately the reactions that occuroccur

1923 Johannes Bronsted (Danish) 1923 Johannes Bronsted (Danish) & Thomas Lowry (English) – & Thomas Lowry (English) – working independently came up working independently came up with the same theorywith the same theory

Brønsted -LowryBrønsted -Lowry

Definition of an Definition of an AcidAcid–An acid is a proton donorAn acid is a proton donor

Definition of a Definition of a basebase–A Base is a proton acceptorA Base is a proton acceptor

DetailDetail

HCl +HCl + HH22OO HH33OO + + + Cl + Cl- -

AcidAcid basebase

DonatesDonates acceptsaccepts

a protona proton a protona proton

Therefore these obey the B/L definitionTherefore these obey the B/L definition

Ammonia GasAmmonia Gas

NHNH3 3 ++ HH22OO NHNH44 + + + OH + OH- -

basebase acidacid

accepts accepts DonatesDonates

a protona proton a protona proton

Therefore these obey the B/L definitionTherefore these obey the B/L definition

What to learnWhat to learn

Water can act Water can act as an acid or as an acid or a base - a base - amphotericamphoteric

Can be applied to non aqueous Can be applied to non aqueous reactionsreactions

HClHCl + + NHNH33 NHNH44++ ++

ClCl--

AcidAcid basebase

Brønsted –Lowry broadens the definition of Brønsted –Lowry broadens the definition of what can act as an acid or a basewhat can act as an acid or a base

HomeworkHomework

Questions 12.1 in textbook and 12.1 in Questions 12.1 in textbook and 12.1 in workbookworkbook

Conjugate acid-base pairsConjugate acid-base pairs

Add acetic acid (ethanoic acid) to waterAdd acetic acid (ethanoic acid) to water

CHCH33COOHCOOH + H+ H22OO CHCH33COOCOO-- + H+ H33OO

The reaction works in both directionsThe reaction works in both directions




DonatesDonates acceptsaccepts

A protonA proton a protona proton



CHCH33COOCOO-- + H+ H33O O CH CH33COOHCOOH + +

HH22OO

AcceptsAccepts DonatesDonates

A protonA proton a protona proton

The water is behaving like an acidThe water is behaving like an acid




The reaction works in both directions so we The reaction works in both directions so we call each conjugate pairscall each conjugate pairs

CHCH33COOH is a conjugate acid of CHCOOH is a conjugate acid of CH33COOCOO--

CHCH33COOCOO- - is a conjugate base of CHis a conjugate base of CH33COOHCOOH

An acid changes into a conjugate base An acid changes into a conjugate base when it donates a proton when it donates a proton

CHCH33COOHCOOH CHCH33COOCOO-- HH++

acidacid Conjugate Conjugate protonproton

basebase

A base changes into a conjugate acid A base changes into a conjugate acid when it accepts a protonwhen it accepts a proton

CHCH33COOCOO-- HH+ + CHCH33COOHCOOH

basebase proton proton conjugate acidconjugate acid

Every acid has a conjugate base and Every acid has a conjugate base and every base has a conjugate acid...every base has a conjugate acid...

We call this an conjugate acid - base pairWe call this an conjugate acid - base pair

A conjugate acid – base pair is any pair A conjugate acid – base pair is any pair consisting of an acid and a base which consisting of an acid and a base which differs by one protondiffers by one proton

ImportantImportant

The definition says that the pair must involve The definition says that the pair must involve a single proton so...the conjugate pair of a single proton so...the conjugate pair of HH22SOSO44

HSOHSO44--

ExampleExample

What is the conjugate acid and the What is the conjugate acid and the conjugate base of HCconjugate base of HC22OO44

--

To change into its conjugate the base To change into its conjugate the base must accept a proton...somust accept a proton...so

HCHC22OO44-- ++ HH++ H H22CC22OO4 4

basebase conjugate acidconjugate acid

ExampleExample

What is the conjugate acid and the What is the conjugate acid and the conjugate base of HCconjugate base of HC22OO44

--

To change into its conjugate the acid must To change into its conjugate the acid must donate a proton...sodonate a proton...so

HCHC22OO44-- C C22OO4 4

2 -2 - ++ HH++

AcidAcid conjugate baseconjugate base

Tell meTell me

Which is the acid and which is the baseWhich is the acid and which is the base

HNOHNO33 + + HH22FF22 HH22NONO33 + + HFHF22

Also mark out the pairsAlso mark out the pairs

HNOHNO33 + + HH22FF22 HH22NONO33 + + HFHF22

Conjugate acid-base pair

Conjugate acid-base pair

Acid AcidBase Base

NeutralisationNeutralisation

Neutralisation is the Neutralisation is the reaction between an reaction between an acid and a base to acid and a base to form salt and waterform salt and water

NeutralisationNeutralisation

Acids and base in the correct proportions Acids and base in the correct proportions cancel each other outcancel each other out

This means they lose their This means they lose their characterisitics,the acid is no longer characterisitics,the acid is no longer behaving like and acid and vice versabehaving like and acid and vice versa

The resulting solution has a neutral effect The resulting solution has a neutral effect on litmus paperon litmus paper

exampleexample

HCl + NaOHHCl + NaOH NaClNaCl+ H+ H22OO

The word salt simply refers to the fact that The word salt simply refers to the fact that the hydrogen in the acid is replaced by a the hydrogen in the acid is replaced by a metal or ammonium ionmetal or ammonium ion

What’s Happening?What’s Happening?

HCl + NaOHHCl + NaOH NaClNaCl+ H+ H22OO

In soln:In soln:

HH++ + Cl + Cl - - + Na + Na + + + OH + OH - - NaNa + + + Cl + Cl - - = = HH22OO

Lets ignore the spectator ionsLets ignore the spectator ions

HH++ + Cl + Cl - - + Na + Na + + + OH + OH - - NaNa + + + Cl + Cl - - = = HH22OO

The hydrogen (hydronium) ions The hydrogen (hydronium) ions from the acid are reacting with from the acid are reacting with the hydroxide ions from the the hydroxide ions from the base to form water which base to form water which results in a neutral solutionresults in a neutral solution

Everyday examplesEveryday examples

Stomach HCL neutralised by NaHCOStomach HCL neutralised by NaHCO33

– In other words...by an antacid (bioSodol) In other words...by an antacid (bioSodol) containing sodium hydrogencarbonatecontaining sodium hydrogencarbonate

HCl + NaHCOHCl + NaHCO33 NaCl + HNaCl + H22O + COO + CO22

Another example (Maalox)Another example (Maalox)

2HCl + Mg(OH)2HCl + Mg(OH)22 MgCl + HMgCl + H22OO


Calcium Oxide (lime) spread on soil to Calcium Oxide (lime) spread on soil to neutralize the acid conditionsneutralize the acid conditions

CaO + HCaO + H22O O Ca(OH)Ca(OH)22

Lime + waterLime + water Calcium HydroxideCalcium HydroxideCalcium Hydroxide can neutralize acidity as followsCalcium Hydroxide can neutralize acidity as follows

Ca(OH)Ca(OH)2 2 + H+ H22SOSO44 CaSOCaSO4 4 + 2H+ 2H22OOCalcium hydroxide plus Sulfuric Acid becomes Calcium Sulfate and WaterCalcium hydroxide plus Sulfuric Acid becomes Calcium Sulfate and Water


Limestone added to lake water to Limestone added to lake water to neuralise the effects of acid rainneuralise the effects of acid rain

CaCOCaCO3 3 + H+ H22SOSO44 CaSOCaSO4 4 + 2H+ 2H22O + O +

COCO22

Calcium carbonate plus Sulfuric Acid becomes Calcium Sulfate and Calcium carbonate plus Sulfuric Acid becomes Calcium Sulfate and Water and Carbon DioxideWater and Carbon Dioxide

HomeworkHomework

Questions 12.2 – 12.6 in textbook and Questions 12.2 – 12.6 in textbook and 12.2 – 12.4 in workbook12.2 – 12.4 in workbook

acids and bases. acids definition : latin meaning sour “acidus” lots of acids –dangerous...

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