chapter 7 acids n bases

7/29/2019 Chapter 7 Acids n Bases

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SMK DR MEGAT KHAS, IPOH

KELAS : 4 SC 1

SUBJEK : KIMIA

TARIKH :

MASA :

GURU : Juni Farhana Bt Hassan

SIRI PELAJARAN : /2013

TOPIK : Acids And Bases

CHAPTER 7

ACIDS AND BASESTHE STRENGTH OF ACIDS AND BASE

BASE

DEFINITION CHEMICAL PROPERTIES CHEMICAL REACTION

ROLE OF WATER IN ACID AND BASE

ACIDS

DEFINITION CHEMICAL PROPERTIES CHEMICAL REACTION

CONCENTRATION OF ACIDS AND ALKALIS

MOLARITY

STANDARD SOLUTION

NEUTRALISATION


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SMK DR MEGAT KHAS, IPOH

KELAS : 4 SC 1

SUBJEK : KIMIA

TARIKH :

MASA :

GURU : Juni Farhana Bt Hassan

SIRI PELAJARAN : /2013

TOPIK : ACIDS

DEFINITION OF ACIDS

An acid is a chemical substance which ionises in water to produce hydrogen

ions, H+.

HCl + H2O H3O + Cl`

HCl H+

+ Cl`

Example acid:- HCl, HNO3, H2SO4Acid can classify as a monoprotic acid or diprotic acid based on basicity.

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

Example: HCl is known as monoprotic acid since it ionized/ dissociates in

water to produce one hydrogen ion H+

HCl H+

(aq) + Cl`

(aq)

Example: H2SO4 is known as diprotic acid since it ionized / dissociates in

water to produces two hydrogen ion H+

H2SO4 2 H+

+ SO42-

USES OF ACIDS

Sulphuric Acid - detergents, electrolytes, paints, fertilizers

Nitric Acid - plastic acids, fertilizers

Ethanoic Acid As a preservative

PROPERTIES OF ACIDS

Taste sour Corrosive Turn blue litmus paper to red Has pH value below 7 (1-6) can conduct electricity in aqueous solution since ..

.

.

DEFINITION OF BASES AND ALKALI

A base is a chemical substances that reacts with an acid to form salt and water

only.

According to Arrhenius : A base is a chemical substance which ionizes in water to

produced hydroxides ions , OH-

Some bases can dissolve in water and known as alkalis.which ionizes in water to

produce hydroxide ions OH-

KOH K+

+ OH-

NaOH Na+ + OH-

Example of Alkalis : Sodium Hydroxide, NaOH, KOH.(metal hydroxides)

Example of bases :CuO Copper Oxide, PbO ..(metal oxides)

USES OF ALKALIS AND BASES

Ammonia nitric acid, fertilizers, cleaning agent

Sodium Hydroxide- detergent, soap, bleaching agents.

Magnesium hydroxide toothpaste

PROPERTIES OF ALKALI

Taste bitter and feels smooth Corrosive Turn red litmus paper to blue Has pH value above ( 8 14) can conduct electricity in aqueous solution since ..

.

.


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ROLE OF WATER OF ACIDS

An acid only shows its acidic properties, when it is dissolved in water.

Without water, an acids still exists as molecules since there are no hydrogen ions H+

ion present. Therefore in solid form acid will not show acidic properties

However in the presence of water, the acids ionizes to form hydrogen ions, H+

. This

caused the acid to show its acidic properties.

ROLE OF WATER OF ALKALIS

An alkalis only shows its alkaline properties, when it is dissolved in water.

Without water, an alkalis still exists as molecules since there are no hydroxide ions

OH

+

ion present. Therefore in solid form alkalis will not show alkaline properties

However in the presence of water, the alkalis ionizes to form hydroxide ions,O H+

.

This caused the alkalis to show its alkaline properties.

CHEMICAL REACTION OF ACIDS- HCl, HNO3, H2SO4

React with metal oxide to form salt and water

React with reactive metals to produce salts and hydrogen gas

React with metal hydroxide to form salt and water

React with carbonates to produce salts, water and carbon dioxide

CHEMICAL REACTION OF ALKALIS - NaOH, KOH, MgO

React with acids to form salt and water

React with metal ion to produce metal hydroxide

React with ammonium salt to produce salt, water and ammonia gas.

THE STRENGTH OF ACIDS AND ALKALIS

pH SCALE

The pH scaled is used to indicate the concentration of the hydrogen ion and hydroxide

ions.

It consists pH values that range from 0 to 14

pH value less than 7 acidic solution pH values equals 7 neutral solution pH palues greater than 7 alkaline solution.

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

a. Universal Indicator

b. Acid base Indicator

c. pH meter

a. Universal Indicator

strong acid : red weak acid : orange/ yellow strong alkali : deep blue, purple weak alkali: blue neutral : green

b. Acid base Indicator

Methyl Orange Phenolphthalein Litmus Paper

Acid : RedNeutral : Orange

Alkali : Yellow

Acid : ColourlessNeutral : Colourless

Alkali : Pink

Acid : Blue turns to redAlkali : Red turns to blue


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STRONG AND WEAK ACIDS

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

A strong acid is an acid which ionises or dissociates completely in water to produces hydrogen ion..

Example of strong acid: Hydrochloric acid, HCl

HCl H+

+ Cl`

A weak acid is only partially ionised in water.Example of weak acid: Ethanoic acid , CH3COOH

CH3COOH H+

+ CH3COO-

STRONG ACID WEAK ACID

Hydrocholoric acid,

Nitric acid, HNO3Sulphuric acid, H2SO4

Carbonic acid, H2CO3Ethanoic acid, CH3COOH

Sulphurous acid, H2SO3

The smaller pH values, the stronger the acid, concentration of H+

ion increase

STRONG AND WEAK ALKALIS

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

A strong alkali is an alkali which ionises or dissociates completely in water to produces hydroxide ions.

Example of strong alkali : Sodium hydroxide, NaOH

NaOH Na+

+ OH`

A weak alkali is only partially ionised in water.

Example of weak alkali : Ammonia , NH3

NH3 + H2O N H4+

+ OH-

STRONG ALKALI WEAK AlKALI

Sodium Hydroxide, ( )

Potassium Hydroxide, ( )Barium Hydroxide , ( )

Ammonia, NH3

Hydrazine, N2H4

The higher pH values, the stronger the alkali, concentration of OH-ion increase

RELATIONSHIP BETWEEN Ph VALUES, MOLARITY OF ACIDS AND

ALKALIS

For acids, the lower the pH value, the higher concentration of hydrogen

ions,

Compare pH value between pH 1 and pH 5

Shows that pH 1 has higher concentration of hydrogen ion, H+

compared to pH 5Therefore pH 1 is strong acid


For alkalis, the higher pH value , the higher the concentration of

hydroxide ions


Shows that pH 13 has higher concentration of hydroxide ion, OH-

compared to pH 8

Therefore pH 13 is strong alkalis


RELATIONSHIP BETWEEN MOLARITY AND pH VALUES OF ACIDS

0.1 mol dm-3

HNO3 0.01 mol dm-3

HNO3 0.0001 mol dm-3

HNO3

pH 1 pH 2 pH 3

Conclusion:

RELATIONSHIP BETWEEN MOLARITY AND pH VALUES OF ALKALIS

0.1 mol dm-3

NaOH 0.01 mol dm-3

NaOH 0.0001 mol dm-3

NaOH

pH 13 pH 12 pH 11

Conclusion:


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CONCENTRATION OF ACIDS AND ALKALIS

The concentration of solution either acids or alkalis depends on the amount of

solute dissolved in a given volume solution.

The greater the amount of solute dissolved, the higher the concentration of

the solution.

Therefore the concentration of a solution refers to the quantity of solute in agiven volume solution.

1. Concentration ( g/dm3) = Mass of solute (g)

Volume of solution (dm3)

2. Molarity (mol/dm3) = Number of moles of solute (mol)

volume of solution (dm3)

3. Molarity ( mol/dm3) = Concentration (g dm

-3)

Molar mass

*Always make sure that the volume of solution in dm3

1 dm3

= 1000 cm3

FORMULAE 1 : . Concentration ( g/dm3) = Mass of solute (g)

Volume of solution (dm3)

Example 1:

4.0 g of sodium hydroxide, NaoH is dissolved in water to make 200 cm3

of solution.

What is the concentration of the solution in g dm-3

Example 2

A 400 cm3

salt solution was evaporated to dryness and 18.0 g of sodium chloride, NaCl

was left behind. Calculate the concentration in g dm-3

FORMULAE 2: Molarity (mol/dm3) = Number of moles of solute (mol)

volume of solution (dm3)

Example 3

What is the molarity of a solution prepared by dissolving 0.15 mole of ammonia

enough distilled water to make 250 cm3

Example 4

Find the molarity of solution which is prepared by dissolving o.30 mol of sodium

hydroxide, NaOH in distilled water to make up 350 cm3

FORMULAE 3: Molarity ( mol/dm3) = Concentration (g dm

-3)

Molar mass

Example 5

The molarity of a bottle of nitric acid, HNO3 solution is 2.0 mol dm-3

. What is the

concentration of the solution in g dm-3

.[Relative atomic mass: H;1 N;14, O;16]

Example 6

Calculate the molarity of ammonia nitrate NH4NO3 solution with a concentration of

8.0g dm-3

Example 7

A 200 cm3

solution was found to contain 24.5g of dissolved sulphuric acid. What is the

molarity of the acid in solution. [ Realative atomic mass: H;1 S;32, O;16]


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chapter 7 acids n bases

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