Acids and Bases
Acids and Bases
Acids and Bases
Acids
An acid is a substance that produces
hydrogen ions, H+ when it is dissolved in
water.
The hydrogen ions that are produced in
water are responsible for the properties of
acids.
Formula
hydrochloric acid
sulfuric acid
nitric acid
ethanoic acid
HCl
H2SO4
HNO3
CH3COOH
Ions produced in
water
H+(aq), Cl(aq)
H+(aq), SO42(aq)
H+(aq), NO3(aq)
H+(aq), CH3COO(aq)
Properties of acids
Solutions of acids in water have the following
general properties.
Acids have a sour taste.
Acids turn moist blue litmus red.
Solutions of acid in water conduct
electricity.
ZnCl2(aq) + H2(g)
CuSO4(aq) + H2O(l)
Cu(NO3)2(aq) + 2H2O(l)
Bases
A base is any
metal oxide containing oxide ions, O2
or a metal hydroxide containing
hydroxide ions, OH
Formula
Na2O
CuO
Mg(OH)2
NaOH
Ions involved
Na+, O2
Cu2+, O2
Mg2+, OH
Na+, OH
Properties of bases
Neutralisation:
A base reacts with an acid to produce a
salt and water only. This reaction is
known as neutralisation.
salt + water
For example,
(i) zinc oxide + sulphuric acid
zinc sulphate + water
ZnO(s) + H2SO4(aq)
ZnSO4(aq) + H2O(l)
When represented as an ionic equation,
ZnO(s) + 2H+(aq)
Zn2+(aq) + H2O(l)
(ii) magnesium hydroxide + nitric acid
magnesium + water
nitrate
Mg(OH)2(s) + 2HNO3(aq)
Mg(NO3)2(aq) + 2H2O(l)
H2O(l)
Alkalis
Alkalis are a special class of bases which
can dissolve in water to produce ions, OH
An example of soluble base is sodium oxide
which dissolves in water to give sodium
hydroxide.
Na2O(s) + H2O(l)
2NaOH(aq)
Properties of alkalis
Alkalis have a bitter taste and soapy feel.
Alkalis turn moist red litmus paper blue
Alkalis produce hydroxide ions in water.
NaOH(aq)
Na+(aq) + OH (aq)
salt + water
(base)
For example,
NaOH(aq) + HCl(aq)
NaCl(aq) + H2O(l)
The ionic equation for this reaction is,
OH(aq) + H+(aq)
H2O(l)
NH3(g) + H2O(l)
acids
alkalis
neutral
solutions
pH value
less than 7
Examples
hydrochloric acid, sulphuric acid,
nitric acid, ethanoic acid
(vinegar), lime juice, fizzy drinks
etc
more than 7 sodium hydroxide, potassium
hydroxide, aqueous ammonia,
soaps, detergents, tooth paste
etc
exactly 7
pure water
Universal indicator
The pH value of a colourless solution can
be measured using the Universal
Indicator which is a mixture of dyes.
Solutions of different pH produce different
colours when tested with the Universal
Indicator. Thus, pH can be used for
comparing acids and alkalis of the same
concentration
Colour in Colour in
acidic
alkaline
solutions solutions
methyl orange
red
phenolphthalein colourless
litmus
red
yellow
pink
blue
pH range at
which the
colour
canges
35
8 10
58
Ca2+(aq) + H2O(l)
Types of oxides
An oxide is formed when an element
combines with oxygen. Oxides can be
classified as four types depending on
their properties
sulfurous acid
H2SO3(aq)
H2CO3(aq) (carbonic acid)
calcium + water
carbonate
CaCO3(s) + H2O(l)
Acidic oxide
Formula Physical
Acid formed
state
when dissolved
in water
sulfur dioxide
SO2
gas
sulfurous acid,
H2SO3
sulfur trioxide
SO3
gas
sulfuric acid,
H2SO4
carbon dioxide
CO2
gas
carbonic acid,
H2CO3
phosphorous(V)
P4H10
solid
phosphoric acid,
oxide
H3PO4
potassium hydroxide
2KOH(aq)
MgO(s) + H2SO4(aq)
magnesium
sulphate +
water
MgSO4(aq) + H2O(l)
For example,
- In reaction (a) with sulfuric acid, lead behaves as a basic
oxide forming a salt (lead sulphate) and water.
- In reaction (b), with sodium hydroxide, lead(II) oxide
behaves as an acidic oxide forming a salt (sodium
plumbate(II)) and water.
(a) Lead(II) oxide + sulfuric acid
lead(II) sulfate + water
PbO(s) + H2SO4(aq) PbSO4(aq) + H2O(l)
(b) Lead(II) oxide + sodium hydroxide sodium + water
plumate(II)
PbO(s) + 2NaOH(aq) Na2PbO2(aq) + H2O(l)
Acidic
oxide
Basic
oxide
Amphoteric
oxide
Physical
may exist solids at
solids at
state at
as gases toom
room
room
or solids temperature temperature
temperature
Formation
formed by formed by
nonmetals
metals
Solubility in usually
water
soluble in
water to
form
acids
mostly
insoluble. A
few basic
oxides
dissolve in
water to
form
alkalis, e.g
Na2O, K2O
Neutral
oxide
usually
gases or
liquids
formed by
formed by
some metals some nonmetals
mostly
insoluble in
water
usually
insoluble in
water
Acidic
oxide
Basic
oxide
Amphoteric
oxide
Neutral
oxide
Test with
litmus
paper
solutions in
water turn
blue litmus
red
if soluble in
water,
solutions
turn red
litmus blue
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Reaction
with acids
do not
react with
acids
reacts with
acids to
form salt
and water
reacts with
both acids
and bases to
form a salt
and water
do not
react with
acids or
bases
Reaction
react with
with bases alkalis to
form a salt
and water
Examples
CO2,SO2
---
H2O, CO,
N2O