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NAVODAYA VIDYALAYA SAMITI, NOIDA

E-CONTENT FOR CLASS X SCIENCE

ACIDS BASES AND SALTS (CHAPTER-2)

Prepared by

LIGI V VASUDEVAN, PGT CHEMISTRY

JNV IDUKK

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INTRODUCTION

ACIDS are

- Sour in taste

-Changes the blue colour of blue litmus to red

- Common examples are citric acid, lactic acid

BASES are

- bitter in taste & soapy to touch

- Changes the blue colour of red litmus to blue

- Common examples are washing soda, baking soda

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INDICATORS AND THEIR COLOUR CHANGES

SAMPLE SOLUTIONS	LITMUS	PHENOPHTHALEIN	METHYL ORANGE
ACID	BLUE TO RED	COLOURLESS	RED
BASE	RED TO BLUE	PINK	YELLOW

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OLFACTORY INDICATORS

Substances whose odour (smell) changes in acidic or basic media are called olfactory indicators. The common olfactory indicators are

onion cloves vanilla

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How do acids and bases react with metals?

Acids react with metals to form salt and hydrogen gas
ACID + METAL--------------🡪 SALT + HYDROGEN
eg:- Zn + 2HCl---------------🡪 ZnCl₂ + H₂
Fe + H₂SO₄-----------🡪 FeSO₄ +H₂
Bases also react with metal to form hydrogen
BASE + METAL--------------🡪 SALT + HYDROGEN
Eg:- 2NaOH +Zn -------------🡪 Na₂ZnO₂ +H₂

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Hydrogen gas burns with a pop sound

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How do metal carbonates & bicarbonates react with acids?

Metal carbonates/Bicarbonates + Acid -----🡪Salt +Water+ Carbon dioxide

Na₂CO₃ + 2HCl----------------🡪 2NaCl + H₂O + CO₂
NaHCO₃ +HCl-----------------🡪 NaCl + H₂O + CO₂

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Detection of carbon dioxide

Carbon dioxide turns lime water milky due to the formation of calcium carbonate
Ca(OH)_{2 (aq)} + CO_{2 (g)} -------------🡪 CaCO_{3 (s)} +H₂O _(l)
On passing excess carbon dioxide the milkiness disappear due to the formation of soluble calcium bicarbonate
CaCO_{3 (s)} + H₂O _(l)+ CO_{2 (g)} -------------🡪 Ca(HCO₃)_{2 (aq)}

(soluble in water)

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How do acids and bases react with each other?

The effect of an acid is nullified by a base and vice versa
Acid and base react with each other to form salt and water. This reaction is called NEUTRALISATION REACTION
Example NaOH + HCl -------------🡪 NaCl + H₂O

Ca(OH)₂ + H₂SO₄ ------------🡪 CaSO₄ + 2 H₂O

General Equation:- Acid + Base ------------🡪 Salt + Water

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Reaction of metallic oxide with acids

Why do we use tamarind, lemon etc to clean metal vessels?
The coating over the metal vessels (metal oxide) reacts with acid and get dissolved forming salt and water
METAL OXIDE + ACID --------🡪 SALT + WATER
This is similar to reaction of a base
So metal oxides are BASIC in nature.

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Reaction of non metallic oxides with base

Non metal oxide react with base to form salt and water just like acids
Ca(OH)_{2 (aq)} + CO_{2 (g)} -------------🡪 CaCO_{3 (s)} +H₂O _(l)

base non metaloxide salt water

This reaction shows that non metallic oxides are ACIDIC in nature.

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What do all acids have in common?

All acids produce hydrogen ion (H⁺) or hydronium ion(H₃O⁺)in the presence of water
HCl +H₂O --------------🡪 Cl^- + H₃O⁺
H+/H₃O⁺is responsible for the electrical conductivity of acidic solutions
Some substances do not form H+ ions in aqueous solution even though element hydrogen is present in the compound. They are not acids. Example glucose, alcohol etc

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What have all bases in common?

All bases produce hydroxide ion (OH^-) or hydroxyl ion in the presence of water
NaOH_(aq) --------------🡪 OH^-_(aq) + Na⁺_(aq)
Ca(OH)_2(aq) ------------🡪 2OH^-_(aq) +Ca²⁺_(aq)
Hydroxide ion is responsible for the electrical conductivity of basic solutions

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Dilution of acids

Acid must be slowly added to water, Since dilution is exothermic
Otherwise it may cause burns due to acid splash and can cause breakage of glass containers.
Mixing an acid or base with water decreases the

concentration of ions per unit volume

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pH scale

It is a scale for measuring hydrogen ion concentration in a solution

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Importance of pH in everyday life

Our body pH is 7.0 to 7.8
When rain water has pH less than 5.6 it is acid rain
Plants need a specific pH for the growth. So we need to check the soil pH

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Our stomach produces hydrochloric acid. Too much of acid causes

indigestion, pain and irritation.

To get rid of the acidity bases called ANTACIDS are used.eg:-milk of magnesia.

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Tooth enamel (calcium phosphate) gets corroded by acids produced by bacteria which acts on food particles remaining in our mouth.
To prevent this we use tooth pastes which are basic
Bees and ants inject acid when they sting. So a mild base on the stung area gives relief. You can use soap / tooth paste/ baking soda

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Some naturally occurring acids

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pH of salts

An acid is formed by the reaction between an acid and a base.
The pH of salts depends on the strength of original acid and base

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Chemicals from common salt

Common salt( Sodium chloride) is an important raw material for substances like sodium hydroxide, bleaching powder, baking soda, washing soda and many more

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Sodium hydroxide (NaOH)

When electricity is passed through brine(aq solution of sodium chloride), chlorine is formed at cathode and hydrogen at anode. NaOH is formed near cathode. This process is known as CHLOR-ALKALI process.
2NaCl +2H₂O----------------🡪 2NaOH + H₂+Cl₂

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Bleaching powder- calcium oxy chloride- CaOCl₂

It is formed by the action of chlorine on dry slaked lime
Ca(OH)₂ + Cl₂--------------🡪 CaOCl₂ + H₂O
Uses
For bleaching cotton, linen, wood pulp
As an oxidizing agent
For disinfecting

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Baking soda- sodium bicarbonate- NaHCO₃

Preparation : NaCl +H₂O +NH₃ +CO₂----------------🡪NH₄Cl + NaHCO₃
On heating it produces large amount of carbon dioxide

2NaHCO₃ ----------------------🡪 Na₂CO₃ +H₂O +CO₂

Uses

For making baking powder (a mixture of baking soda + edible acid like tartaric acid) .

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Uses of baking soda

Cake becomes soft and spongy because baking powder when mixed in water or heated the following reaction takes place
NaHCO₃ + H⁺----------------🡪 CO₂ +H₂O + sodium salt of acid
As an antacid against acidity
In fire extinguishers

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Washing soda- Sodium carbonate deca hydrate� Na₂CO₃ 10 H₂O

Preparation : Recrystallisation of sodium carbonate
Na₂CO₃ +10 H₂O -------------🡪 Na₂CO₃10H₂O
Uses
In the manufacture of glass, cement, soap, borax
Cleaning agent
For removing permanent hardness of water

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Are the crystals of salts really dry?

Water of crystallization is fixed number of water molecules chemically attached to each formula unit of a salt

Blue Copper sulphate crystals (CuSO_4.5H₂O)

seems to be dry contain water of crystallization

On heating, water is removed and it turns

White.(CuSO₄)

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Plaster of Paris- Calcium sulphate hemihydrate�- CaSO₄ 1/2H₂O or (CaSO₄)₂H₂O

On mixing with water Plaster of Paris becomes hard solid mass of gypsum
CaSO₄ 1/2H₂O +3/2H₂O-------------🡪 CaSO₄2H₂O (gypsum)
One molecule of water is shared by 2 water molecules in POP
Uses
In making toys, decoration materials
In making surface smooth
For immobilizing broken bone

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IMPORTANT LINKS FOR RESOURCE MATERIALS

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Assignment questions

Define olfactory indicators. Give example
What is neutralization reaction?
Why do acids not show acidic behavior in the absence of water?
Why does distilled water not conduct electricity where as rain water does?
What do you mean by water of crystallization?
Write the equation of “chlor alkali “ process.
What happens when a solution of sodium bicarbonate is heated?