Bases in chemistry- Class X Notes

Base definition and its properties

Definition of base and its properties is most important topic of NCERT Acids bases salt chapter 2 in Class 10. Questions are frequently asked in the CBSE board and ICSE Board exam from bases .

“Chemistry – Define base : class 10 notes “ will be very beneficial for the students who are engaged in the preparation of upcoming board exam.

In this topic, the following terms will be illustrated.

Contents :

* 1. Definition of base

* 2. What are alkalis

* 3. Physical Properties of base

* 4. Chemical Reactions of base

* 5. Uses of common Bases

Base definition

Base are the substance which neutralize the acid to form salt and water only .

Bases exist in two form

Metal oxide
Metal hydroxide

According to Arrhenius principle,

Those substances which dissociate into hydroxide ions in aqueous solution are called base.

NaOH = Na⁺ + OH^-

NH₄OH = NH₄⁺+ OH^-

^Alkalis:

Water soluble bases are also known as alkalis.
Strong Alkalis : NaOH, KOH
Moderately strong alkalis: Mg(OH)₂, Ca(OH)₂, Ba(OH)₂
Weak alkalis : NH₄OH

Soluble bases are much more useful than insoluble bases because most of chemical reaction take place only in aqueous solution.

Strong alkali:

A base whose all molecules dissociate into hydroxide ( hydroxyl) ions is called strong alkali.

e.g. NaOH, KOH

Moderately strong alkalis:

A base whose few molecules dissociate into hydroxyl ions is called moderately strong alkali.

e.g. Mg(OH)₂, Ca(OH)₂, Ba(OH)₂

Weak alkali:

A base whose very few molecules dissociate into hydroxyl ions is called weak alkali.

e.g. NH₄OH

Common Name of Alkalis

* NaOH - Caustic soda

* KOH - Caustic potash

* Mg(OH)₂ - Milk of magnesia

* NH₄OH - Ammonia solution, ammonia water, aqueous ammonia, or aqua ammonia

* Ca(OH)₂ - slaked lime

Note : Limewater is the common name for a saturated solution of calcium hydroxide.

Properties of Bases:

Physical Properties:

Bases have bitter tase.

Bases feel soapy to touch.

Bases turn red litmus blue.

Bases conduct electricity in aqueous solution. i.e bases are electrolyte.

Chemical Reactions:

Alkalis NaOH, KOH	+ Metal →	Salt + H₂
	+ Acid →	Salt + H₂O
	+ Non-Metal Oxide →	Salt + H₂O

Reaction With Some Metals:

Bases react with some metals like Zn, Al, Pb, Sn to form salt and hydrogen gas.

Base + Metal → Salt + H₂

e.g.

2NaOH + Zn → Na₂ZnO₂ + H₂

2NaOH + Pb → Na₂PbO₂ + H₂

2NaOH + Sn → Na₂SnO₂ + H₂

2NaOH + 2Al + 2H₂O → 2NaAlO₂ + 3H₂

Note :

Na₂ZnO₂ is sodium zincate.

Na₂PbO₂ is sodium Plumbate.

Na₂SnO₂ is sodium Stanate.

NaAlO₂ is sodium meta aluminate.

Reaction With Acid:

Base react with acid to form salt and water.

Base + Acid → Salt + Water

NaOH + HCl → NaCl + H₂O

Reaction With Non-metal oxide (Acidic oxide ) :

Base react with Non-metal oxide to form salt and water.

Base + Acidic oxide → Salt + Water

Ca(OH)₂ (aq) + CO₂ (g) → CaCO₃ (s) + H₂O

Uses of Bases:

Mg(OH)₂ :

It is used as antacid to neutralize excess acid in the stomach.
It is called milk of magnesia.

Na₂CO₃ :

It is used as washing soda.
It is used for softening hard water.

NaHCO₃ :

It is used as baking soda in cooking.
It is used for making baking powder.
It is used as antacid.
It is used in fire extinguisher.

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Tuesday, June 8, 2021