117 different chemical elements are
known to us. These elements combine to
form a large number of compounds.
On the basis of their properties all the
compounds can be classified into- Acids,
bases and Salts.
An indicator is a dye that changes color
when it is put into an acid or a base.
Common indicators- Litmus, Methyl
orange and Phenolphthalein.
An acid turns blue litmus to red.
A base turns red litmus to blue.
Methyl orange indicator gives red color in
Methyl orange indicator gives yellow color
in basic solution.
Phenolphthalein is colorless in acid solution.
Phenolphthalein gives pink color in basic
Litmus is a natural indicator. It is a purple
dye extracted from a type of plant
It is neither acidic nor basic.
Turmeric- contains a yellow dye which
turns red in basic solution.
The red cabbage extract which is
neutral in nature remains red in acidic
solution but turns green on adding to
Onion has a characteristic smell . When
basic solution is added to a strip treated
with onions then the smell can’t be
detected. Acids don’t have any effect.
Vanilla extract has a characteristic
pleasant smell. In basic solution the smell
can’t be detected whereas acids do not
destroy the smell.
Acids are sour in taste and turn blue
The acids present in plant materials and
animals are called organic acids.
Organic acids are weak acids
The acids prepared from the minerals of
the earth are called mineral acids.
The mineral acids are strong acids.
Acids have a sour taste.
Acids turn blue litmus red.
Acid solutions conduct electricity.
Acids react with metals to form
Metal + Acid → Salt + Hydrogen gas
Eg. Zn(s) +H₂SO₄(aq)→ ZnSO₄ +H₂(g)
Acids react with metal carbonates to
from carbon dioxide gas.
Metal carbonate +Acid → Salt + carbon dioxide +Water.
Na₂CO₃(s) + 2HCl(aq) → 2NaCl (aq) +CO₂(g) +H₂O(l)
Acids react with bases to form salt and
water. This is called neutralization
Acid + Base → Salt + Water
NaOH (aq) + HCl (aq) → NaCl (aq) + H₂O (l)
Acids react with metal oxides to form salt
Metal oxide + Acid → Salt + Water
CuO (s) + 2HCl (aq) → CuCl₂ (aq) + H₂O (l)
Acids have corrosive nature.
The mineral acids cause severe burns on
the skin and attack and eat up meterials
like cloth, wood, metal and stone work.
An acid is a substance that releases H+
ions in an aqueous solution
› Aqueous means water
Example: when hydrochloric acid is
dissolved in water, the compound
separates into chlorine ions (Cl-) and
hydrogen ions (H+)
A strong acid breaks down completely in
water and gives off many H+ ions
A weak acid only partially breaks down.
It gives off much less H+ than a strong
Sulphuric acid is used in manufacture of
fertilizers (like ammonium sulphate ),
paints ,dyes ,chemicals, plastics,
synthetic fibres, detergents, explosives
and car batteries.
Nitric acid is used for making fertilizers ,
explosives, dyes and plastics.
Hydrochloric acid is used for removing
oxide film before galvanizing.
A base is a substance that releases
hydroxide (OH-) ions in an aqueous
Example: When sodium hydroxide
(NaOH) is dissolved in water, the
compound separates into sodium ions
(Na+) and hydroxide ions (OH-)
The solution of substances like caustic soda,
lime(chuna) and washing soda are bitter in
taste and soapy to touch.
Bases are those chemical substances which
have a bitter taste
Most of the bases do not dissolve in water
those bases which dissolve in water without
any chemical reaction have a special
name .They are called alkali.
Example- NaOH, KOH, Ca(OH)₂, NH₂OH.
Bases usually taste bitter
Bases feel slippery
Bases contain hydroxide ions (OH-)
Bases are the chemicals opposites of acids.
A base is a chemical substance which can
neutralize an acid.
All the metal oxides and metal hydroxides
For example- Sodium oxide(Na₂O) is a metal
oxide so it is a base and Sodium
hydroxide(NaOH) is a metal hydroxide , so it
is a base.
A base is a substance which dissolves in
water to produce Hydroxide ions(OH⁻
NaOH(s) → Na⁺ (aq) + OH⁻ (aq)
KOH(s) → K⁺ (aq) + OH⁻ (aq)
A common property of all the bases is that they
produce hydroxide ion when dissolved in water.
Base/Alkali Sodium ions Hydroxide ions
Base/Alkali Pottasium ions Hydroxide ions