chapter 7 (acids & bases)

7/29/2019 Chapter 7 (Acids & Bases)

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ACIDS & BASES

Definition of acid/ base/ alkali

Properties of acid/ base/ alkali

Role of water on acid / base

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ACID AND BASE

Meaning:An acid is a chemical substance which ionises

in water to produce hydrogen ions, H+ or

hydroxonium ion, H3O+.

A base is a chemical substance which reacts

with acid to produce salt and water

A alkali is a chemical substance which ionizes

in water to produce hydroxide ions, OH-

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Strong Acid, Weak Acid

Strong acid: Acid which ionizescompletely when dissolve in water to

produce high concentration of

hydrogen ion, H+

Example: HCl, HNO3, H2SO4

HCl H+ + Cl-

H+ + H2O H3O+

(Hydroxonium ion)

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Cont.

Weak acid: Acid which ionises

partially when dissolve in water to

produce low concentration of

hydrogen ion, H+

Example: Ethanoic acid

CH3

COOH CH3

COO- + H+

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Strong Alkali, Weak Alkali

Strong alkali: Alkali which ionizescompletely when dissolve in water to

produce high concentration of hydroxide

ion, OH-

Example: NaOH, KOH

Weak alkali: Alkali which ionises partially

when dissolve in water to produce low

concentration of hydroxide ion, OH-

Example: NH3(aq)

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Basicity of Acid

Basicityof an acid is the maximum numberof hydrogen ions that is produced when one

molecule of an acid ionizes in water

Monoprotic acid: Hydrochloric acid, HCl

and nitric acid, HNO3.

e.g : HClH+ + Cl-

Diprotic acid : Sulphuric acid, H2SO4

e.g: H2SO4 2H+ + SO42-

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Cont

Triprotic acid: Phosphoric acid, H3PO4

e.g: H3PO4 3H+ + PO4

3-

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Physical Properties of Acid

Acids have a sour taste Solution of acids has pH less than 7

Solution of acid change blue litmus

paper to red. Aqueous solution of acids are

electrolytes because the presence of

freely moving ions (H+)

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Chemical Properties of Acid

Acid + metal salt + hydrogen gas2HCl(aq) + Mg(s) MgCl2(aq) + H2(g)

Acid + basesalt + waterH2SO4(aq) + CuO (s)CuSO4(aq) + H2O(l)

Acid + alkali salt + waterHNO3 + NaOH(aq) NaNO3 + H2O

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Cont..

Acid + carbonate metal salt + water

+ carbon

dioxide

2HCl + CaCO3 CaCl2+ H2O + CO2

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ROLE OF WATER IN ACIDS &

BASES

An acid shows its acidic properties

only when it is dissolved in water.

This is because without water, an acid

still exits as molecules and there areno hydrogen ions, H+ present.

In the dry acid, the ions in the acid

are fixed in the lattice positions.

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Physical Properties of Alkali

a bitter taste

pH greater then 7

change red litmus paper to blue

Aqueous solution of alkalis are

electrolytes because the presence of

freely moving ions.

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Chemical Properties of Alkali

Acid + alkali

salt + water

HNO3 + NaOH NaNO3 + H2O

Alkali + metal ion insoluble metal

hydroxide2OH- + Mg2+Mg(OH)2

Alkali + ammonium salt

salt + water + ammoniaNaOH + NH4ClNaCl + H2O + NH3

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USES

Uses of acids Uses of bases and alkalis

* Make industrial products such as

paints, detergents, fertilizers.

* Food preservative such as

vinegar, citric acid and ascorbicacid.

* Electrolyte in lead-acid

accumulator.

* Use as laboratory reagents

* Make soaps, shampoos and

detergents.

* Make several of medicines, such

as antacid and aspirin.* Use as laboratory reagents

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Molarity (mol dm-3

) = Number of MoleVolume, dm3

Example: Calculate the molarity of 0.4 moles sulphuric acid

in 250cm3 solution.

Solution :Number of mole = MV

1000

Molarity =number of mole x 1000 = 0.4 x 1000250 250

= 1.6 mol dm-3

CONCENTRATION

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chapter 7 (acids & bases)

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