Chemistry Form 4_acid and Base_ppt

IN SUBTOPIC1 ACIDS AND BASES2 THE STRENGTH OF ACIDS AND

ALKALIS

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CHEMISTRY FORM 4

CONTENT

CREDIT

QUIZ WEBLINK

CONCEPT MAP

GLOSSARY

Dissolves in water forming

BASEACID

1 2 3 4 5 6 7 8 9 10 11 12 13 14

pH SCALES

ALKALI

Weak alkaliStrong alkali

Which ionizes partially

as a

Which ionizes

completely as a

OH-(aq)

contains

Weak acidStrong acid

Which ionizes partially

as a

Which ionizes

completely as a

H+(aq)

contains

Neutral

More alkalineMore acidic

ACIDS AND BASES

THE STRENGTH OFACIDS AND ALKALIS

INTRODUCTION At the end of the lesson,students should be able to:

Analysing characteristicsand properties of acids

and bases

Synthesising the conceptsof strong acids, weak acid,

strong alkalis and weakalkalis

LEARNING OBJECTIVES

INTRODUCTION

Click on the box to see this video

ACIDS

BASES AND ALKALIS

USES OF ACIDS, BASES AND ALKALIS

ROLE OF WATER & THE PROPERTIES OF ACIDS

ROLE OF WATER & THE PROPERTIES OF ALKALIS

CHEMICAL PROPERTIES OF ACIDS

CHEMICAL PROPERTIES OF ALKALIS

Arrhenius definition of acid:

An acid is a chemical substance which ionises in water to produce hydrogen ions, H+.

Example: Hydrochloric acid, HCl

Sulfuric acid, H2SO4

Nitric acid, HNO3

ACIDS

TIPS

H Cl + +O

H H

O+

H H HCl-

HCl (aq) + H2O (l) H3O+ (aq) + Cl- (aq)

ACIDS

HOT TIPS

The definition of an acid contains two important concepts:

(a)Ionises in water

(b)Produces H+ ion

The hydrogen ion is responsible for all acidic properties.

ACIDS

• Monoprotic acid

Acid that produce only one hydrogen ion per molecule of acid.

Example: Hydrochloric acid, HCl

Nitric acid, HNO3

ACIDS

H+ Cl- +H Cl

HCl (aq) H+ (aq) + Cl- (aq)

one hydrogen ion

ACIDS

Diprotic acidAcid that produce two hydrogen ions per molecule of acid.

Example: Sulfuric acid, H2SO4

Carbonic acid, H2CO3

ACIDS

H+ H+ SO42- +

H2SO4 (aq) 2H+ (aq) + SO42- (aq)

two hydrogen ions

H HSO4

ACIDS

Basicity of an acid is the number of ionisable hydrogen atoms per acids molecule.

ACIDS

BASES AND ALKALIS

Arrhenius definition of base:

A base is a chemical substance which ionises in water to produces hydroxide ions, OH-.

Example: Sodium hydroxide, NaOH

Potassium hydroxide, KOH

Ammonia, NH3

TIPS

+ +O

H H

N

H H HN+

H H H

H

H

O-

NH3(aq) + H20 (l) NH4+ (aq) + OH- (aq)

BASES AND ALKALIS

HOT TIPS

The definition of an alkali contains two important concepts:

(a)Ionises in water

(b)Produces OH- ion

The OH- ion is responsible for all basic properties.

Acids and alkalis are electrolytes because their aqueous solutions contain mobile ions that can conduct electricity.

BASES AND ALKALIS

bases alkalis

Bases that can dissolves in water

A chemical substances

which ionises in water to produce

hydroxide ions, OH-

BASES AND ALKALIS

USES OF ACIDS, BASES AND ALKALIS

To use as laboratory reagents

To manufacture and preserve food

To make various medicines

To produce detergents, soaps and shampoos

ROLE OF WATER AND THE PROPERTIES OF ACIDS

Acid ionises in water to produces hydroxonium ions.

The properties of acid can only be exhibited in the presence of water.

Acids cannot show their properties in dry state or when dissolved in organic solvent.

Sour taste pH less

than 7Conduct electricity

Change blue litmus paper red

React withActive metals

Metal carbonate

PROPERTIES OF ACID

+HCl

HClHCl

HH O

HH O

HH OCl-

H

H

HO+

H

H

HO+Cl-

HCl (aq) + H2O (l) H3O+ (aq) + Cl- (aq)

When a pieces of dry blue litmus paper is dropped into each of the three beakers:

No changes in colour


Blue litmus paper turns

red

ROLE OF WATER AND THE PROPERTIES OF ACIDS

An alkali will only exhibit alkaline properties when water is present.

Water is needed to produce free mobile hydroxide ions, OH- in alkalis to exhibit alkaline properties.

For example, sodium hydroxide will only exhibit alkaline properties when water is present.

ROLE OF WATER AND THE PROPERTIES OF ALKALIS

Bitter taste pH more

than 7Conduct electricity

Change red litmus paper blue

React withMetal ion

Ammonium salt

PROPERTIES OF ALKALI

+

When a pieces of dry red litmus paper is dropped into each of the three beakers:

HH O

HH O

HH O

OHNa

OHNa

OHNa OH-

Na+

OH- Na+

NaOH (aq) + H2O (l) Na+ (aq) + OH- (aq)



Red litmus paper turns

blue

ROLE OF WATER AND THE PROPERTIES OF ALKALIS


Acid + Base Salt + Water

H2SO4 (aq) + ZnO (s) ZnSO4 (aq) + H2O (l)

Sulphuric acid

Zinc oxide Zinc sulphate

Water

REACTION WITH BASE

Acids posses the following chemical properties:

React with base

React with metal

React with metal carbonate

Acid + Metal Salt + Hydrogen gas

2HCl (aq) + Mg (s) MgCl2 (aq) + H2 (g) Hydrochloric

acidMagnesium

Magnesium chloride

Hydrogen gas


REACTION WITH METAL

Acid + Carbonate Salt + Water + Carbon dioxide

2HNO3 (aq) + CuCO3 (s) Cu(NO3)2 (aq) + H2O (l) + CO2 (g) Nitric acid

Copper(II) Carbonate

Copper(II) nitrate

Water Carbon dioxide

REACTION WITH METAL CARBONATE


Alkali + Acid Salt + Water

NaOH (aq) + HCl (s) NaCl (aq) + H2O (l)

Sodium Hydroxide

Hydrochloric acid

Sodium chloride

Water

REACTION WITH ACID


Alkalis posses the following chemical properties:

React with acids

React with metal ions

React with ammonium salts

Alkali + Metal ion Insoluble metal hydroxide

2OH- (aq) + Cu2+ (s) Cu(OH)2 (s)Hydroxide

ionCopper(II)

ion

Copper(II) hydroxide

(blue precipitate)

REACTION WITH METAL ION


Alkali + Ammonium salt Salt + Water + Ammonia gas

NaOH (aq) + NH4Cl (aq) NaCl (aq) + H2O (l) + NH3 (g)

Sodium Hydroxide

Ammonium chloride

Sodium chloride

WaterAmmonia

gas

REACTION WITH AMMONIUM SALT


THE PH SCALE

STRONG AND WEAK ACIDS

STRONG AND WEAK ALKALIS

THE PH SCALE

The pH value measures the concentration of hydrogen ions or hydroxide ions.

pH < 7 acidic solution

pH = 7 neutral solution

pH > 7 alkaline solution

THE PH SCALE

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

NeutralIncreasingly alkalineIncreasingly acidic

Concentration of H+ ions increases

Concentration of OH- ions increases

pH

The pH value of an aqueous solution can be measured by using:

Universal Indicator

pH meter

Acid-base indicator

THE PH SCALE

THE PH SCALE


Acids can be classified into strong acid and weak acids.

The strength of an acid depends on the degree of dissociation or ionisation of the acid in water.

TIPS

ACID

STRONGACID

WEAKACID


STRONG ACID

Acid that dissociates completely in water to form hydrogen ions, H+.

Its degree of dissociation is 1 or 100%.

Have high concentration of H+.

Example: Hydrochloric acid, sulphuric acid, nitric acid, and phosphoric acid.

WEAK ACID


Acid that only partially dissociated in water.

Its degree of dissociation is less than 1.

Have low concentration of H+.

Example: Carbonic acid, ethanoic acid and citric acid.

HOT TIPS

The definition of a strong acid contains two important concepts:

(a)Ionises completely in water

(b)Produces a high concentration of H+ ion



STRONGACID

WEAKACID

H

H H

O

C

O -C

H

H

H

H

O

C

O

C

H

H H

HO

CO

C

H

H

H

H

O

C

O

C H

H

H

H

O

C

O

C

Ethanoic acid, CH3COOH

Ethanoate ion,

CH3COO-

Hydrogen

ion, H+

CH3COOH


H+

H+ Cl- H+

H+

H+

Cl-

Cl-

Cl-Cl-

H+

HClHydrogen ion, H+

Chloride ion,Cl-



Alkalis can be classified into strong alkalis and weak alkalis.

The strength of an alkali depends on the degree of dissociation of the alkali in water.

TIPS

ALKALI

STRONGALKALI

WEAKALKALI

Alkali that dissociates completely in water to form hydroxide ions, OH-.

Its degree of dissociation is 1 or 100%.

Have high concentration of OH-.

Have high pH value (pH 13 – pH 14).

Example: Sodium hydroxide, potassium hydroxide, and calcium hydroxide.

STRONG ALKALI



Alkali that is only partially dissociated in water.

Its degree of dissociation is less than 1.

Have low concentration of OH-.

Example: Ammonia

WEAK ALKALI

HOT TIPS

The definition of a strong alkali contains two important concepts:

(a)Ionises completely in water

(b)Produces a high concentration of OH- ion



STRONGALKALI

WEAKALKALI

H

H

H

H

N+

H

H

HN

H

O-

H

H

HN

H

H

HN

H

H

HN

H

H

HN H

H

HN

NH3Hydroxide

ion,OH-

Ammonia, NH3

molecule

Ammonium ion, NH4

+


Na+

OH-

Na+

Na+

Na+

Na+

OH-

OH-

OH-OH-

Hydroxide ion, OH-

Sodium ion, Na+

NaOH


1

OBJECTIVES

2 3 4 5 6 7 8 9 10

1.An acid is any substance whichproduces

A. Strong burns

B. Metal ions in solution

C. Hydrogen ions in water

D. A red colour in water

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2. An example of a strong acid is

A. Ethanoic acid

B. Citric acid

C. Nucleic acid

D. Hydrochloric acid

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3. A strong acid is one which

A. Has a high concentration

B. Has a low concentration

C. Is completely ionised in water

D. Is only partly ionised in water

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4. An acid will

A. Have a pH less than 7

B. Have a pH more than 7

C. Turn moist litmus paper blue

D. Turn universal indicator purple

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5. A diprotic acid is an acid that

A. can form only one product when it reacts with a base

B. produces two hydrogen ions per molecule

C. reacts with one type of base only

D. contains two hydrogen atoms per molecule

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6. Which of the following solution will not containhydroxide ions?

A. Ammonia in water

B. Ammonium hydroxide in tetrachloromethane

C. Sodium oxide in water

D. Sodium metal in water

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7. Which of the following gases will changemoist litmus paper from red to blue?

A. Carbon dioxide

B. Oxygen

C. Ammonia

D. Hydrogen dioxide

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8. A liquid has a pH of 7 must be

A. Neutral

B. Tasteless

C. Colourless

D. Soluble

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9. Which of the following regarding pH is true? A. pH is measure of how acidic or alkaline a

solution in water

B. The pH of pure water is 9

C. The lower the pH value the less acidic isthe solution

D. The higher the pH value the less alkalineis the solution

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10. Which of the following compounds produceshydrogen ions when dissolves in water?

A. Ammonia

B. Sodium chloride

C. Potassium hydroxide

D. Concentrated sulphuric acid

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Basicity The number of ionisable hydrogen atoms per acids molecule.

Diprotic acid Acid that produce two hydrogen ions per molecule of acids.

Dissociation A general process in which ionic compounds (complexes, molecules, or salts) separate or split into smaller molecules, ions, or radicals, usually in a reversible manner.

Monoprotic acid

Acid that produce only one hydrogen ion per molecule of acid.

Hydroxonium ion

The resulting additional hydrogen ion in the water (as H30+)

Inference The act or process of deriving logical conclusions from premises known or assumed to be true.

Ionisation The physical process of converting an atom or molecule into an ion by adding or removing charged particles such as electrons or other ions.

Prepared by:Mazian Binti Mat Yasin

D20061026425AT16 (Chemistry)

Supervisor:Pn. Noorshida bt Mohd Ali

WEB LINK

http://www.visionlearning.com/library/module_viewer.php?mid=58

http://www.chem4kids.com/files/react_acidbase.html

http://en.wikibooks.org/wiki/General_Chemistry/Acids_and_bases_neutralize_each_other#Arrhenius_Theory

http://www3.interscience.wiley.com:8100/legacy/college/pratt/0471393878/student/review/acid_base/index.html

http://www.funsci.com/fun3_en/acids/acids.htm












http://www.funsci.com/fun3_en/acids/acids.htm

Chemistry Form 4_acid and Base_ppt

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