Chapter - 2, Acids Bases and Salts Notes

Notes Chapter - 2 Acids, Bases and Salts

ACIDS:
• These are the substances which have sour in taste.
• They turns blue litmus solution to red.
• They give H   ions in aqueous solution

Examples of Acids : -
HCl - Hydrochloric Acid


BASES
• These substances are bitter in taste.
• They turns red litmus solution to blue.
• They give OH ions in aqueous solution. 
Examples of Bases : -
NaOH - Sodium Hydroxide
KOH - Potassium Hydroxide
Alkalis  - These are the bases soluble in water. like - NaOH (sodium Hydroxide)


INDICATORS
There are the substance that changes their colour / smell in different types of substances.

Types of Indicators
l. Natural Indicators - Those indicators found in nature by trees called Natural Indicators
Ex - Litmus, Turmeric

2. Synthetic Indicators - These are the chemical substance prepare in laboratories.
Ex- Phenolphthalein, Methyl Orange

3. Olfactory indicators - These substance have different odour in acids and Bases.
Ex - Onion, clove oil, Vanilla Essence.

Chemical properties of Acids Bases

Reactions of Metals with Acids and Bases

With Acids : -

Metal    +   Acids    →  Salt    +    Hydrogen gas

Ex – 2HCl    +   Zn    →  ZnCl₂    + H₂

With Bases : -

Metal    + Base  →   Salt    +    Hydrogen gas

Ex – 2NaOH    +    Zn   →  Na₂ZnO₂     +   H₂

** Hydrogen gas released can be tested by bringing burning candle near gas bubbles, it burst with pop sound.

Reaction of Metal Carbonates /Metal Hydrogen Carbonated with

Acid : -

Acid   +  Metal Carbonate / Metal Hydrogen Carbonate → Salt  +  CO₂  +H₂O

Ex – 2HCl + Na₂CO₃   → 2 NaCl  +  CO₂  +H₂O

HCl + Na₂HCO₃   →  NaCl  +  CO₂  +H₂O

** Metal Carbonate / Metal Hydrogen Carbonate not react with Bases.

CO₂ Can be tested by passing it through lime water

Ca(OH)₂  +  CO₂  →  CaCO₃  + H₂O

Lime water [Ca(OH)₂] turns milky when Carbon dioxide passes through it

When excess CO₂  passes the milkiness disappears

Reaction of Acids and Bases with Each Other

Acid  +  Base   →  Salt   +  H₂O

Neutralisation Reaction – Reaction of acid with base is called as neutralisation reaction

Ex – HCl  +  NaOH  →   NaCl  + H₂O

Reaction of Metallic Oxides with Acids

Metallic Oxides are basic in nature. Like MgO, CaO etc.

Metallic Oxide  +    Acid  → Salt  +  H₂O

Ex – CaO  +  2HCl  →  CaCl₂  +  H₂O

Reaction of Non – Metallic Oxides with bases

Non – Metallic oxides are acidic in nature

Non – Metallic Oxides  + Base → Salt   + H₂O

Co₂  +  Ca(OH)₂   → CaCO₃  +  H₂O

All Acids have in Common

• ·   All acids have H⁺ ions in common
• ·   Acids produces H⁺  ions  in solution which are responsible for their acidic nature

All Bases have in Common

• ·   All bases have OH^- ions in common
• ·  These OH^- are responsible for their basic nature

Acids in water solution

Acids produces H⁺  ions  in presence of water. But these H⁺ ions cannot exist alone, they exist as H₃O⁺ (hydronium ions).

         H⁺  +  H₂O  →  H₃O⁺  

Bases in water solution

Bases when dissolved in water gives OH^- ions. Those bases are soluble in water are called Alkali.

Important

While diluting acids, it is recommended that the acid should be added to water and not water to acid because the process of dissolving an acid or a base in water is highly exothermic.

Universal Indicator

Strength of acid or base can be estimated using universal indicator. It is mixture of several indicators. It shows different colours at different concentrations of H⁺ ions present in the solution.

pHScale -

pH Scale – It is a scale for measuring H⁺  ions concentration in a solution.  It have reading 0 to 14

• ·    pH = 7 → neutral solution
• ·    pH less than 7 → acidic solution
• ·    pH more than 7 →   basic solution

 Importance of pH in Everyday life

• ·    Plants and animals are pH sensitive they need specific pH for their healthy growth
• ·    pH of our Stomach is about 1 or 2 as our stomach Produce HCl
• ·    pH cause Tooth decay when pH of our mouth is lower the 5.5
• ·    When the pH of rain is less than 5.6 it is called acid rain
• ·   Bee sting leaves an acid which cause pain to get over this pain we have to apply baking soda on stung area.

Salt

Salt is an ionic compound foamed in neutralisation reaction

Chemicals from Salts : -

1 – Sodium Hydroxide (NaOH)

When electricity is passes through an aqueous solution of NaCl (brine), it decomposes to form NaOH

2NaCl  +  2H₂O → 2 NaOH  +  Cl₂  +  H₂

At anode – Cl₂ gas release

At cathode – H₂ gas release

Near cathode -  NaOH solution is formed.

Uses of these products

• ·   H₂ used as fuels and margarine
• ·   Cl₂ used as water treatment, PVC, CFC’s
• ·   NaOH used as degreasing metals, soaps and paper making
• ·   Cl₂  +  NaOH  combine used as bleach fabrics

2 – Bleaching Powder (CaOCl₂)

It is produced by the action of chlorine on dry slaked lime

 Cl₂  +  Ca(OH)₂  →   CaOCl₂  +  H₂O

Uses of Bleaching powder

·         Bleaching cotton and linen in textile industry.

·         Bleaching wood pulp in paper factories

·         Oxidizing agent in chemical industries

·         Disinfecting drinking water.

3 – Baking Soda ( sodium Hydrogen Carbonate)  (NaHCO₃)

It foamed when CO₂ passed through aqueous Sodium Chloride

• ·    It is mild non-corrosive base
• ·    When it is heated during cooking it foamed sodium carbonate and CO₂ release from it

Uses of Baking Soda : -

• ·   For making baking powder ( mixture of baking soda and tartaric acid) When baking power is heated or mixed with water, CO₂ is produced which causes bread and cake to rise making them soft and spongy.
• ·   An ingredient in antacid
• ·   Used in soda acids, fire extinguishers

4 – Washing Soda (Na₂CO₃.10H₂O) ( Sodium carbonate deca hydrate)

Recrystallization of sodium carbonate gives washing soda. It is a basic salt.

 Na₂CO₃  +  10H₂O →  Na₂CO₃.10H₂O

Uses of Washing Soda : -

• ·   In glass, soap and paper industries
• ·   Manufacture of borax
• ·   Cleaning agent for domestic purposes
• ·   For removing permanent hardness of water

5 – Plaster of Paris - POP (Na₂CO₃. H₂O)  ( Calcium sulphate hemi hydrate)

On heating gyspsum (Na₂CO₃.2 H₂O) at 373 K, it loses one and half molecules of water and becomes Plaster of Paris (POP)

It is a white powder and on mixing with water it changes to gypsum.

 Na₂CO₃. H₂O  +  H₂O   →   Na₂CO₃ 2 H₂O

Uses of POP

• ·    Doctors use POP for supporting fractured bones.
• ·    For making toys, materials for decoration
• ·    For making surfaces smooth. 

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