|– Sour in taste
||– Bitter in taste|
|– Change the blue litmus to red
||– Change red litmus to blue|
||eg. Sodiumhydroxide NaOH|
|– AceticAcid CH3 COOH
| Some Naturally occuring acids|
|Sour milk (Curd) –
|Ant and Nettle sting –
Acid – Base Indicators – Indicate the presence of an acid or base in a
Litmus solution – It is a natural indicator. It is a purple day extracted from
Lichens. Other examples are Red Cabbage and coloured petals of Petunia
Olfactory indicators – Show odour changes in acidic or basic media. eg. onion and clove.
Dilute Acid : Contains only a small amounts of acid and a large amount of
Concentrated Acid : A concentrated acid contains a large amount of acid and a small amount of water.
Chemical Properties of Acids and Bases
Acid + Metal --> Salt + Hydrogen
Pop test : When a burning candle is brought near a test tube containing hydrogen gas it burns with a ‘Pop’ sound. This test is conducted for examining the presence of hydrogen gas.
Base + Metal --> Salt + Hydrogen
NaOH + Zn --> Na2ZnO2 + H2
Note – Such reactions are not possible with all the metals.
Strength of an Acid or Base
Strength of acids and bases depends on the no. of H+ions and OH–ions
With the help of a universal indicator we can find the strength of an acid or
base. This indicator is called PH scale.
pH = Potenz in German means power.
This scale measures from 0 (very acidic) to 14 (very alkaline) 7 Neutral
(water in Neutral).
pH paper : Is a paper which is used for measuring PH.
– strong Acids give rise to more H+ions.
eg. HCl, H2SO4 and HNO3.
– Weak Acids give rise to less H+ ions
eg. CH3 COOH, H2 CO3 (Carbonic acid)
– Strong Bases – Strong bases give rise to more OH– ions.
eg. NaOH, KOH, Ca(OH)2
– Weak Bases : give rise to less OH– ions.