ACIDS, BASES AND SALTS.pdf

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ACIDS, BASE
S

AND SALTS




Indicators

Synthetic

Methyl orange

Phenolphthalein

Natural

Dyes
(
Indicators
of colour
)

Olfactory

Indicators of
smell

Onion extract

Clov
e oil

Va
n
illa essence

Red lit
m
us

Blue lit
m
us




Indicator

Colour in acidic solution

Colour in basic solution


Blue litmus solution


Red litmus solution


Phenolphthalein


Methyl orange

Red

No colour change

Colourless

Pink

No colour change

Blue

Pink

Yellow



Physical properties of Acids and
Bases
:

Acids

Bases

→

Sour taste

→

Turns blue litmus to red

→

Provides H
+

ions


when dissociated

→

pH less than 7


→

strong acids



HCl, HNO
3
,



H
2
SO
4


→

weak acids



H
2
CO
3



CH
3
COOH



H
3
PO
4

→

Bitter taste

→

Turns red litmus to blue

→

Provides OH
–

ions


when dissociated

→

Bases dissolve in


water to give alkalies

→

pH more than 7 upto 14


→

strong base



NaOH, KOH


→

weak base



NH
4
OH



Chemical properties of Acids and Base
s:

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Type of Reaction

Acid

Base

1.

Neutralization
reaction

Acid + Base
→

Salt + H
2
O

Example:

HCl + NaOH

→

NaCl + H
2
O

Acid + Base
→

Salt + water

Example:

CaO + HCl(aq)
→

CaCl
2
(aq) + H
2
O

(l)

2.

Reaction with
metals

Acid + Metal
→

Metallic salt + H
2
(g)

Example:

Zn(s) + dil H
2
SO
4

(aq)
→

ZnSO
4

(aq) +
H
2
(g)

Base + Metals
→

Salt + H
2
(g)

Exa
mple:

NaOH + Zn
→

Na
2
ZnO
2

+ H
2

Only active metals like Zn and Al

reacts
with bases
.

3.

Reaction with
carbonates

Acid + Carbonates
→

Metallic salt +
CO
2
(g) + H
2
O

Example:

Na
2
CO
3
+ H
2
SO
4

→

Na
2
SO
4

+ H
2
O + CO
2

Base + carbonate
→

No rea
ction

4.

Reaction with

bicarbonates

Acid + Bicarbonates
→

Metallic salt +
CO
2
(g) + H
2
O

Example
:

NaHCO
3
+ HCl
→

NaCl + H
2
O + CO
2

Base +
bi
carbonate
→

No rea
ction

5.

Reaction with
oxide

Acid + Metal Oxide

→

Salt + H
2
O

Example
:

CaO + HCl

(aq)
→

CaCl
2

(aq) + H
2
O

Base + Non
-
metallic

oxide
→

Salt +
water

Example:

Ca
(
OH
)
2

+ CO
2
→

CaCO
3

+ H
2
O

6.

Dissolution in
water

Acid gives H
+

ions in water.

Examples:

HCl

(aq)

→

H
+

+ Cl
–

H
2
SO
4

(aq)

→

2H
+

+
−
2
4
SO

Bases gives OH
–

ions in water.

Examples:

NaOH

(aq)

→

Na
+

+ OH
–

Ca(OH)
2

(aq)

→

Ca
2+

+ 2(OH)
–



Strength of acids & bases

•

Strong Acids and strong bases when dissolved in water dissociate completely into
(H
+
) and (OH
–
) ions respectively.

•

Weak acids and weak bases when dissolved in water dissociate partially into (H
+
)
and (OH
–
) ions respectively. Rather then remain in molecular form.

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pH SCALE


pH scale:

A scale of numbers from 0 to 14 on which
the strength of an acid or base is measured is known as pH
scale.


pH is defined as negative logarithm of
]
O
H
[
or
]
H
[
3
+
+


i.
e.
]
O
H
log[
pH
or
]
H
[
log
pH
3
+
+
−
=
−
=


0

7

14

Acidic

Neutral

Basic

Increasing

H
+
ions

Decreasing

H
+
ions

H
2
O

CO

N
2
O




Importance of pH in everyday life:


(i)

In digestive system
→

(i) acidic in stomach (ii) basic (alkaline) in duodenum


(ii)

Tooth decay


(iii)

Nature of soil


(iv)

Plants and Animals are pH sensitiv
e


(v)

Self defense by animals and plants through chemical warfare



SALTS :
They

are the neutralization products of acids and bases.


Classification of Salts :

Salts can be classified after ‘salt hydrolysis’.

Type of
salts

Hydrolysis of salts

1.

pH = 7

S
alts of strong acid and strong bases

Example:
4
2
4
2
SO
K
,
SO
Na
KCl,
NaCl,

)
aq
(
Cl
)
aq
(
Na
)
aq
(
NaCl
O
H
)
s
(
NaCl
2
−
+
+
→
→
+

2.

pH < 7

Salts of strong acids and weak bases

Example:

4
4
CuSO
,
Cl
NH

)
aq
(
Cl
)
aq
(
NH
)
aq
(
Cl
NH
O
H
)
s
(
Cl
NH
4
4
2
4
−
+
+
⎯
→
⎯
⎯
→
⎯
+


O
H
NH
2
4
+
+

+
+
H
OH
NH
4


The solution is acidic due t
o the
+
H

ion produced by the hydrolysis of
+
4
NH

3.

pH > 7

Salt of weak acid and strong base

Example:
COONa
CH
,
CO
Na
3
3
2

)
aq
(
Na
)
aq
(
COO
CH
)
aq
(
COONa
CH
O
H
)
s
(
COONa
CH
3
3
2
3
+
−
+
⎯
→
⎯
⎯
→
⎯
+


−
+
OH
COOH
CH
3

O
H
COO
CH
2
3
+
−



The solution is basic due to hydrolysis

of
)
aq
(
COO
CH
3
−

4.

pH


7

Salt of weak acid & weak base

Example:
4
3
COONH
CH

+
−
+
⎯
→
⎯
⎯
→
⎯
+
4
3
4
3
2
4
3
NH
COO
CH
)
aq
(
COONH
CH
O
H
COONH
CH


−
+
OH
COOH
CH
3

O
H
COO
CH
2
3
+
−




O
H
NH
2
4
+
+

+
+
H
OH
NH
4




Common Salt
→

NaCl
→

Chemicals obtained from NaCl


(i)

NaOH (by chlor
-
al
kali process)

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2
2
Current
Electric
2
H
Cl
NaOH
O
H
NaCl
+
+
⎯
⎯
⎯
→
⎯
+


(ii)

Bleaching power (CaOCl
2
)



2
2
2
2
H
CaOCl
Cl
)
OH
(
Ca
+
⎯
→
⎯
+


(iii)

Baking soda (NaHCO
3
)



3
2
3
Brine
2
NaHCO
CO
NH
O
H
NaCl
⎯
→
⎯
+
+
+









(iv)

Washing soda (Na
2
CO
3

∙ 10H
2
O)



O
H
CO
Na
NaHCO
2
3
2
3
+
⎯
→
⎯




Other Important Salt
s
:


Plaster of Paris

(POP)
→

CaSO
4

∙
O
H
2
1
2

POP
2
4
k
273
Heat
Gypsum
2
4
O
H
2
1
∙
CaSO
O
H
2
∙
CaSO
⎯
⎯
→
⎯






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