important notes of acid & base
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Classification of matter
On the basis of
a) composition – elements, compounds and mixtures
b) state – solids, liquids and gases
c) solubility – suspensions, colloids and solutions
Types of mixtures – homogeneous and heterogeneous
Types of compounds – covalent and ionic
What Is an Acid and a Base?
Ionisable and non-ionisable compounds
An ionisable compound when dissolved in water or in its molten state, dissociates into ions almost entirely. Example: NaCl, HCl, KOH, etc.
A non-ionisable compound does not dissociate into ions when dissolved in water or in its molten state. Example: glucose, acetone, etc.Arrhenius theory of acids and bases
Arrhenius acid – when dissolved in water, dissociates to give H+ (aq) or H3O+ ion.
Arrhenius base – when dissolved in water, dissociates to give OH− ion.
Examples
Acids
Hydrochloric acid (HCl)
Sulphuric acid (H2SO4)
Nitric acid (HNO3)
Bases
Sodium hydroxide (NaOH)
Potassium hydroxide (KOH)
Calcium hydroxide (Ca(OH)2)
Bronsted Lowry theory
A Bronsted acid is an H+ (aq) ion donor.
A Bronsted base is an H+ (aq) ion acceptor.
Example
In the reaction: HCl (aq) +NH3 (aq) →NH+4(aq) +Cl− (aq)
HCl – Bronsted acid and Cl− : its conjugate acid
NH3 – Bronsted base and NH+4 : its conjugate acid
Physical test
Given are two possible physical tests to identify an acid or a base.
a. Taste
An acid tastes sour whereas a base tastes bitter.
The method of taste is not advised as an acid or a base could be contaminated or corrosive.
b. Effect on indicators by acids and bases
An indicator is a chemical substance which shows a change in its physical properties, mainly colour or odour when brought in contact with an acid or a base.
Below mentioned are commonly used indicators and the different colours they exhibit:
a) Litmus
In a neutral solution – purple
In acidic solution – red
In basic solution – blue
Litmus is also available as strips of paper in two variants – red litmus and blue litmus.
An acid turns a moist blue litmus paper to red.
A base turns a moist red litmus paper to blue.
b) Methyl orange
In a neutral solution – orange
In acidic solution – red
In basic solution – yellow
c) Phenolphthalein
In a neutral solution – colourless
In acidic solution – remains colourless
In basic solution – pink
Acid-Base Reactions
Reactions of acids and bases
a) Reaction of acids and bases with metals
Acid + active metal → salt + hydrogen + heat
2HCl+Mg→MgCl2+H2 (↑)
Base + metal → salt + hydrogen + heat
2NaOH+Zn→Na2ZnO2+H2 (↑)
A more reactive metal displaces the less reactive metal from its base.
2Na+Mg (OH) 2→2NaOH+Mg
b) Reaction of acids with metal carbonates and bicarbonates
Acid + metal carbonate or bicarbonate → salt + water + carbon dioxide.
2HCl+CaCO3→CaCl2+H2O+CO2
H2SO4+Mg (HCO3)2→MgSO4+2H2O+2CO2
Effervescence indicates liberation of CO2 gas.
c) Neutralisation reaction
1. Reaction of metal oxides and hydroxides with acids
Metal oxides or metal hydroxides are basic in nature.
Acid + base → salt + water + heat
H2SO4+MgO→MgSO4+H2O
2HCl+Mg (OH) 2→MgCl2+2H2O
2. Reaction of non-metal oxides with bases
Non-metal oxides are acidic in nature
Base + Non-metal oxide → salt + water + heat
2NaOH+CO2→Na2CO3+H2O
Water
Acids and bases in water
When added to water, acids and bases dissociate into their respective ions and help in conducting electricity.
Difference between a base and an alkali
Base-
Bases undergo neutralisation reaction with acids.
They are comprised of metal oxides, metal hydroxides, metal carbonates and metal bicarbonates.
Most of them are insoluble in water.
Alkali –
An alkali is an aqueous solution of a base, (mainly metallic hydroxides).
It dissolves in water and dissociates to give OH− ion.
All alkalis are bases, but not all bases are alkalis.
Hydronium ion
Hydronium ion is formed when a hydrogen ion accepts a lone pair of electrons from the oxygen atom of a water molecule, forming a coordinate covalent bond.
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Answer:
Notes of acid and bases
