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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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