ACIDS, BASES and SALTS

Do you still remember….

• ACIDS

• ALKALIS

• SALTS

HClH2SO4HNO3

CH3 COOH

NaOH

KOHNH4OHCa(OH)2

NaCl

MgCl2K2SO4

ACIDS

What do all acids have in

common?H

SO4

H

NO3

Cl

H

H ALL acids contain HYDROGEN – this

is important!

What can you see common in acids?

HCl

H2SO4

HNO3

ACIDS

What is an ACID ?

An acid is a substance that produces

Hydrogen ions, H , in water+

ACIDS

• Pure acids (without water) consists of small covalent molecules.

• In the presences of water, the acid molecules form ions

ClHwater

H+

(aq)Cl

-

(aq)

When acid molecules forms ions

We say the acid is IONISED

IONISATION

ClHwater

H+

(aq)Cl

-

(aq)

H

HSO4

H NO3

water

water

SO4

2-

(aq)H+

(aq)2

H+

(aq)NO3

-(aq)

Basicity of an Acid

Some acids just form one hydrogen ion when

dissolve in water whereas others form more

than one.

The maximum number of hydrogen ions

produced by a molecule of an acid is called the

basicity of the acid

Basicity of an Acid

ACID Reaction with Water Basicity

Hydrochloric acid

Nitric acid

Ethanoic acidCH3COOH H + CH3COO

Sulphuric acid

H2SO4 2H + SO4

ClHH2O

H+(aq)

Cl-(aq)

NO3HH2O

H+(aq)

NO3-

(aq)

+ -

H2O + 2-

1

1

1

2

BASICITY of ACIDS

• What about Phosphoric acids?H3PO4

TRIBASIC ACID

ACIDS

• Properties of acids are due to the hydrogen ions.

• It is the hydrogen ions that react with metals

ACID: Hydrogen ion is important!

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

2H (aq) 2Cl (aq) Mg(s)

Mg (aq) 2Cl (aq)2

H2 (g)

2H (aq) Mg(s) Mg (aq)2

H2 (g)

SALTS & ACIDS SALTS

• Metal salts are produced when acids reacts with alkali/base, carbonates and metals.

• Examples: NaCl, Na2SO4, Mg(NO3)2

• pH of metal salts are NEUTRAL

SALTS & ACIDS SALTS

• ACID SALTS are produced when dibasic or tribasic acids reacts with alkali/base, carbonates and metals.

E.g. NaHSO4, K2HPO4 , KH2PO4

HOW TO GET IT?

(White board explained by teacher)

Properties of Acid

ACIDS

Sour

Hazardous

+ metals Salt + H2

Changes colour of

indicators

+ carbonates Salt + CO2

+ H2O

+ base/alkali Salt + H2O

Strength of Acid

Strong Acids

A strong acid is one that completely ionises in

water.

Weak Acids

A weak acid is one that partially ionises in

water.

Strong Acids

Strong Acids

A strong acid is one that completely ionises in

water.

H+ Cl-H Cl

H+ Cl-H Cl

H+ Cl-H Cl

H+ Cl-H Cl

HCl(g) H (aq) Cl (aq)

All the HCl molecule ionises into hydrogen ions

and chloride ion

Weak Acids

CH3COO- H+

CH3COOH(aq) H (aq)CH3COO (aq)

HCH3COO

CH3COO H

CH3COO H

CH3COO H

Weak Acids

A weak acid is one that partially ionises in

water.

Strong Acids , Weak Acids

Strong Acid

Total Ionised

CH3COO- H+HCH3COO

CH3COO H

CH3COO H

CH3COO H

H+ Cl-H Cl

H+ Cl-H Cl

H+ Cl-H Cl

H+ Cl-H Cl

Weak Acid

Partially Ionised

USES of ACIDS

ACIDS

Sulphuric acid

Fertilisers, car battery

Sulphuric acid

Paint, artificial fibres, plastics

Ethanoic acid

Food, preservatives

Hydrochloric acid

Stomach (digest food)

ALKALIS

What do all alkalis have in

common?OHNH4

K OH

ALL alkalis contain

HYDROXIDE ions in aqueous

solution(in water)

What can you see common in Alkalis?

KOH

NH4OH

Ca(OH)2Ca

OHOH

ALKALIS

What is an ALKALI ?

An alkali is a substance that produces

hydroxide ions, OH , in water-

BASES

What are BASES?

• Bases are oxides and hydroxides of metals

• E.g. CuO, MgO, NaOH,

BASES and ALKALIS

What is the difference between a

base and an alkali?

• All alkalis are bases, but not all bases are alkalis

• Bases are insoluble and alkalis are soluble in water.

BASES and ALKALIS

BASES

ALKALI

e.g. NaOH

e.g. CuO

Example of an Alkali: Sodium hydroxide (aqueous)

Example of a Base: Copper (II) oxide (Solid)

Properties of Alkalis

ALKALIS

Slippery

Hazardous

+ acids Salt + H2O

Changes colour of

indicators

+ soln metal ions precipitate

+ ammonium compound Salt + NH3 +

H2O

Properties of Bases

DEMONSTRATION OF CHEMICAL EQUATIONS

(White board explained by teacher)

USES of ALKALIS

ALKALIS

Neutralisation

Toothpaste, stomach acid

Soaps

Detergents cleaners

Agriculture

Balancing pH of acidic soil

Grease remover

INDICATORS & pH

Indicators

An indicator is a substance that has

different colours in acidic and alkaline

solutions.

Example:

Phenolphtalein

Methyl orange & Screen methyl orange

Litmus solution or paper

Indicators

Indicator Colour in acids Colour in alkali

Phenolphthalein

Screen methyl orange

Litmus

THE pH SCALE

How to see if an unknown solution is acidic or

alkaline?

How do you know if it is a strong acid or a weak acid or strong alkali or weak alkali?

THE pH SCALE

0 1 2 3 4 5 6 7 8 9 10 1112 13 14

Acids Alkalis

Neutral

More acidic More alkali

Importance of pH

• pH in the body

- Acidic condition Stomach (pH ~ 1.5)

- Alkaline condition s.intestine ( ~ 8.4)

- Blood contains CO2 ( ~ 6.5)

• pH and food preservation

- Ethanoic acid (vinegar) – Preserve veg.

- Benzoic acid – fruit juices, oyster sauce

- Citric acid – use in food for preservation

and flavouring.

Importance of pH

• pH in the garden

- most plants grow best when pH of soil is

~ pH 5.6

- Orchids – more acidic soil pH 4-5

- Strawberries, apples – weakly acidic pH 5-6

- Common vegetables – neutral pH 6-8

Acidic, Basic and Amphoteric Oxides

Acidic Oxide

ACIDIC OXIDES are oxides of NON-METALS

Acidic oxides react with water and produce

acids

Acidic oxide Formula

Acid produced with water

Sulphur trioxide SO3 Sulphuric Acid, H2SO4

Carbon dioxide CO2 Carbonic Acid, H2CO3

Phosphorus (V) oxide

P4O10 Phosphoric acid,

H3PO4

SO2(g) H2O (l) H2SO4(aq)

Acidic Oxide

Acidic oxides react with alkali to form salt and

Water.

The salt sodium carbonate is formed when

carbon dioxide is bubbled into dilute sodium

hydroxide

CO2(g) 2NaOH (aq) Na2CO3(aq)

H2O(l)

Basic Oxide

BASIC OXIDES are oxides of METALS

Basic oxides react with acids to form salt and

water

CaO(s) 2HCl (aq) CaCl2(aq)

H2O(l)

Amphoteric Oxide

Some metallic oxides are amphoteric.

This means they behave as an acidic oxide or

as a basic oxide

Amphoteric oxide Formula

Aluminium oxide Al2O3

Lead (ll) oxide PbOZinc oxide ZnO

Amphoteric Oxide

Amphoteric oxides react with acids and with

alkalis to form salts.

Aliminium oxide acts as:

• a base by reacting with hydrochloric acid

&

• an acid by reacting with sodium hydroxide

solution

Amphoteric Oxide

Aliminium oxide (Al2O3)

Al2O3 6HCl 2AlCl3 3H2OAl2O3

NaOH Sodium aluminate

H2OAl2O3

Amphoteric Oxide

Zinc oxide (ZnO)

2HCl ZnCl2 H2OZnO

NaOH Sodium Zincate

H2O

ZnO

Neutral Oxides

Neutral oxides DO NOT REACT with either

acids or bases, therefore they do not form salts.

Neutral oxide Formula

Water H2OCarbon monoxide CO

Nitrogen monoxide NO