Std10 Science EM 3

Topics: Hydrochloric acid, Acid, PH Pages: 90 (30014 words) Published: July 11, 2015
CHEMICAL REACTIONS
hydrogen atoms. The word 'acid' is derived
from the Latin name ‘acidus’ which means
sour taste. Substances with ‘sour taste’
are acids. Lemon juice, vinegar and grape
juice have sour taste, so they are acidic.
They change blue litmus to red. They are
colourless with phenolphthalein and pink
with methyl orange. Many organic acids are
naturally present in food items.

GROUP ACTIVITY
•• From dawn to dusk observe any 10
chemical changes that take place
around you and classify them.
•• Prepare a table model of a volcano
using
ammonium
dichromate
(vigorous)
•• Prepare a table model of a volcano
using baking soda (silent).
MORE TO KNOW

A substance which alters the rate of
reaction without undergoing any change
in mass and composition is known as
catalyst.

ACIDS, BASES AND SALTS
Hai Vini, you look tired. Take
this fresh lime juice.

Vini :

No, it has a sour taste.

Nivi :

Do you know why it is sour?

Vini :

Sorry, I have no idea.

Nivi :

It is due to the presence of
acid. Let’s learn more about
this.

blue litmus paper

Fig. 11.9 Acid solution turns blue
litmus paper red

Acids, bases and salts are used in
everyday life. Let it be a fruit juice or a
detergent or a medicine. They play a key
role in our day-to-day activities. Our body
metabolism is carried out by means of
hydrochloric acid secreted in our stomach.

11.3. ACIDS

11.3.1 Classification of Acids
1.Based on their sources : Acids
are classified into two types, namely,
organic acids and inorganic acids.
Organic Acids:- Acids present in plants
and animals (living things) are organic
acids eg. HCOOH, CH3COOH (Weak
acids).

Acid is a substance which furnishes
H ions or H3O+ ions when dissolved in
water. Acids have one or more replaceable
+

177

Inorganic Acids:- Acids in rocks and
minerals are inorganic acids or mineral
acids eg. HCl, HNO3, H2SO4 (Strong
acids).

CHAPTER 11

Nivi :

2. Based on their Basicity
Monobasic Acid: - It is an acid which
gives one hydrogen ion per molecule of
the acid in solution, e.g. HCl, HNO3.

Dibasic Acid:- It is an acid which gives
two hydrogen ions per molecule of the
acid in solution, e.g. H2SO4, H2CO3.
Tribasic Acid:- It is an acid which gives
three hydrogen ions per molecule of the
acid in solution, e.g. H3PO4
Source

Acid present

Apple

Malic acid

Lemon

Citric acid

Grape

Tartaric acid

Tomato

Oxalic acid

Vinegar (food
preservative)

Acetic acid

Curd

Lactic acid

3. Based on Ionisation

Acids are classified into two types based
on ionisation.

Strong Acids:- These are acids which
ionise completely in water, e.g.HCl.
Weak Acids:-These are acids which
ionise partially in water, e.g. CH3COOH.

4. 
Based on Concentration:- Based
on the percentage or amount of acid
dissolved in water, acids are classified
into concentrated acids and dilute
acids.

Concentrated Acid:- It is an acid having
a relatively high percentage of acid in its
aqueous solution.

Dilute Acid:- It is an acid having a
relatively low percentage of acid in its
aqueous solution.
MORE TO KNOW

Care must be taken while mixing any
concentrated mineral acid with water.
The acid must always be added slowly
to water with constant stirring. If water
is added to a concentrated acid, a large
amount of heat is generated. The mixture
splashes out of the container and it may
cause burns.

11.3.2 Chemical ­Properties of Acids

CHEMISTRY

MORE TO KNOW

For acids, we use the term basicity which
refers to the number of replaceable
hydrogen atoms present in one molecule
of an acid. For example, acetic acid has
four hydrogen atoms but only one can be
replaced. Hence it is monobasic.

1. Reaction of Metals with Acid
Note that zinc reacts with dilute
hydrochloric acid to form zinc chloride and
hydrogen gas.

Zn + 2HCl → ZnCl2 + H2↑

When a...
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