7_Acids & Bases

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Chapter 7

Acids and Bases

C

hemistry

Form

4

Introduction to cidsand Bases

MENU

ThepH ScaleRole of water and the

properties of acidsRole of water and theproperties of alkalis

Strong and Weak cids Strong and Weaklkalis

Mind Map


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Chem

istryForm4:Introduction

Meaning of Acid

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An acidis a chemical substance which ionisesinwater to produce hydrogen ions, H+.

The acidic propertiesof an acidis due to the

presence of hydroxonium ions, H3O+

. However,this ion can be written as H+, hydrogen ion.

Hydroxonium ion
http://localhost/var/www/apps/conversion/tmp/scratch_5/acid&bases%20video/acid%20charac..AVIhttp://localhost/var/www/apps/conversion/tmp/scratch_5/acid&bases%20video/acid%20ionise.AVIhttp://localhost/var/www/apps/conversion/tmp/scratch_5/acid&bases%20video/H3O%20ions.AVIhttp://localhost/var/www/apps/conversion/tmp/scratch_5/acid&bases%20video/H3O%20ions.AVIhttp://localhost/var/www/apps/conversion/tmp/scratch_5/acid&bases%20video/acid%20ionise.AVIhttp://localhost/var/www/apps/conversion/tmp/scratch_5/acid&bases%20video/acid%20charac..AVI


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Chem


Basicity of Acid

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Basicityof an acidis the maximum numberofhydrogen ionsthat is produced when one molecule

of the acid ionises in water.

Monoprotic acidis an acid which produces one

hydrogen ionwhen one molecule of the acid

ionisesin water.

Nitric Acid


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Chem


Basicity of Acid

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Diprotic acidis an acid which produces two

hydrogen ionswhen one molecule of the acid

ionises in water.

For example : Sulphuric Acid, H2SO4


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Chem


Meaning of Bases / Alkalis

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A alkaliis a chemical substance which ionisesin water to produce hydroxide ions, OH- .

Bases

Alkalis

Alkalisare bases which are soluble in

water.

Basesare oxides/hydroxides of metals

which react with acids.

All alkalis are basesbut not all basesare

alkalis.

_+

Na+ OH -


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Chem


Uses of Acids, Bases and Alkalis

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Substance Uses

Acids

1. Sulphuric acid To make detergents, paints, fertilisers

As electrolyte in lead-acid accumulator.

2. Hydrochloric acid To clean metals before electroplating in

industry.3. Nitric acid To make fertilizers, plastics, explosives.

4. Ethanoic acid To make vinegar.

5. Methanoic acid To coagulate latex in the rubber

industry.6. Carbonic acid To make fizzy drinks
http://localhost/var/www/apps/conversion/tmp/scratch_5/acid&bases%20video/uses%20of%20acids.AVI


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Substance Uses

Bases and Alkalis

1. Ammonia (aqueous) To make fertilisers, cleaning

agents.

To manufacture nitric acid.

To keep latex in liquid form.2. Magnesium hydroxide To make gastric tablets and tooth

paste.

3. Calcium hydroxide To make cement, limewater.

To neutralise acidity of soil.4. Sodium hydroxide To make detergents, soaps,

fertilisers and bleaching agents.

Uses of Acids, Bases and Alkalis
http://localhost/var/www/apps/conversion/tmp/scratch_5/acid&bases%20video/uses%20of%20bases.AVI


8/32ChemistryForm4:Roleofwater&thepropertiesofacids

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ROLE OF WATER ON THEPROPERTIES OF ACID


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ChemistryForm4:Roleofwater&thepropertiesofacids

Role of Water

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An acid only shows it acidic properties whenwater is present.

Liquid glacial

ethanoic acidAqueous

ethanoic acid

Ethanoic acid in

dry propanone
http://localhost/var/www/apps/conversion/tmp/scratch_5/acid&bases%20video/detail%20role%20water-acid.AVIhttp://localhost/var/www/apps/conversion/tmp/scratch_5/acid&bases%20video/detail%20role%20water-acid.AVIhttp://localhost/var/www/apps/conversion/tmp/scratch_5/acid&bases%20video/detail%20role%20water-acid.AVI


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Role of Water

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A pure acid in the dry state does notexhibit its

acidic properties.

Dry acid consists of covalent moleculesonly.

Thus, hydrogen ions are not present.


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Role of Water

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The presenceof waterenables the acid moleculesto ioniseto produce hydrogen ions.

Thus it exhibitsacidic properties.
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emistryForm4:Roleofwater&thepropertiesofacids

Properties of Acids

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Acid + base salt + water Acid + metal salt + hydrogen gas

Acid + metal carbonate salt + water + carbon dioxide gas
http://localhost/var/www/apps/conversion/tmp/scratch_5/acid&bases%20video/HCl+NaOH.AVIhttp://localhost/var/www/apps/conversion/tmp/scratch_5/acid&bases%20video/acid+mg.AVIhttp://localhost/var/www/apps/conversion/tmp/scratch_5/acid&bases%20video/HCl+metal%20carb.(M).avi


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emistryForm4:Roleofwater&thepropertiesofalkalis

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ROLE OF WATER ON THE

PROPERTIES OF ALKALI


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Role of Water

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When water is present, an alkali will dissolve andionises to produce freely moving hydroxide ions.

Thus the alkali exhibitsalkaline properties.

For Example:
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Role of Water

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Without water, a pure alkali in the dry statedoes

notexhibitalkaline propertiesbecause it does

not contain freely moving hydroxide ions.

For example : Aqueous Ammonia Solution


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Role of Water

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Alkali + acid salt + water Alkali + metal ion insoluble

metal hydroxide

Alkali + ammonium salt salt + water + ammonia gas
http://localhost/var/www/apps/conversion/tmp/scratch_5/acid&bases%20video/H2SO4%20+%20(NH4)2SO4.AVIhttp://localhost/var/www/apps/conversion/tmp/scratch_5/acid&bases%20video/HCl+NaOH.AVI


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Role of Water

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Alkali + acid salt + water Alkali + metal ion insoluble

metal hydroxide

Alkali + ammonium salt salt + water + ammonia gas
http://localhost/var/www/apps/conversion/tmp/scratch_5/acid&bases%20video/H2SO4%20+%20(NH4)2SO4.AVIhttp://localhost/var/www/apps/conversion/tmp/scratch_5/acid&bases%20video/HCl+NaOH.AVI


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Chem

istryForm4:ThepHScale

pH Scale

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The pH scaleis used to indicate the degreeof

acidityor alkalinityof a solution. It consists of

pH values that range from 0 to 14.

pH Paper pH Meter


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Chem

istryForm4:ThepHScale

pH Value

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The pH valueis a

measureof theconcentrationof

hydrogen ions, H+and

hydroxide ions, OH-.

The lowerthe pH value,

the higherthe

concentration of hydrogen

ions.

The higherthe pH value,

the higher the

concentration of

hydroxide ions.


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Che

mistryForm4:

ThepHScale

pH value of substances

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C

hemistryForm

4:StrongandWeakAcids

Strong Acids

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The strengthof an acid depends on the degree ofionisationor dissociation of the acid in water.

A strong acidis achemical substance

that dissociates

completelyin water

to produce highconcentration of

hydrogen ions, H+.


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hemistryForm4:StrongandWeakAcid

s

Strong Acids

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H+ + Cl- (100% ionisation )
http://localhost/var/www/apps/conversion/tmp/scratch_5/acid&bases%20video/StrongAcidIonization.exe


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C


s

Weak Acids

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Weak acidsare chemicals that dissociate partially(incomplete dissociation) in water to produce lowconcentration of hydrogen ions.

An example of weak acid is

dilute ethanoic acid,

CH3

COOH.

Most of the ethanoic acid

exist as molecules, few as

CH3COO-and H+ions.
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C


s

Weak Acids

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Partial dissociation

O

CH3 C -OH
http://localhost/var/www/apps/conversion/tmp/scratch_5/acid&bases%20video/WeakAcidEquilibrium.exe


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C

hemistryForm

4:Strongand

WeakAlkalis

Strong Alkalis

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A strong alkaliis a chemical substance thatdissociates completelyin water to produce high

concentration of hydroxide ions, OH-.

For example: Sodium hydroxide, NaOH

dissociation dissociation


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C

hemistryForm

4:Strongand

WeakAlkalis

Weak Alkalis

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A weak alkaliis a chemical substance thatdissociates partially(incomplete dissociation) to

produce low concentration of hydroxide ions, OH- in

water.

For example: Aqueous Ammonia Solution, NH3

High pH value


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7.1Characteristic

sandPropertiesofAcidsandB

ases

Mind Map 1

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7.2Th

eStrengthofA

cidsandAlkalis

Mind Map 2

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7.2Th

eStrengthofA

cidsandAlkalis

Mind Map 3

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Dissociation of Strong and Weak Alkalis

in Water

NH3(aq)NH3(aq)

NH3(aq)

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7_Acids & Bases