Igcse Chemistry Revision NotesO Level Chemistry Revision Notes



Bases are metal oxides and metal Hydroxides.

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A base is a a substance, that can accept H+ ions and therefore are proton acceptor.

Example:Indicators for detecting Acids And Bases

  • Copper(II) Oxide (CuO)
  • Iron(III) Oxide (Fe2O3)
  • Copper (II) Hydroxide (Cu(OH)2)
  • Iron (III) Hydroxide (Fe2O3)

It reacts with an acid to give salt and water only.

Base + AcidArrow used In Chemical EquationSalt + Water

CuO  +  H2SO4Arrow used In Chemical Equation CuSO4  + H2O

Neutralization Reaction:

Neutralization reaction occurs, when Acid and Base react to form Metal Salt and Water.

Acid + BaseArrow used In Chemical EquationMetal Salt   + Water


An Alkali is a base, that is soluble in water.

Lets see what happens when an alkali (Sodium Oxide) is added to water

Na2O   + H2OArrow used In Chemical Equation2NaOH

Examples of Alkalis:

  • Sodium Hydroxide (NaOH)
  • Potassium Hydroxide (KOH)
  • Calcium Hydroxide (Ca(OH)2
  • Barium Hydroxide (Ba(OH)2
  • Aqueous Ammonia (NH3)



  • Alkalis have bitter taste and soapy feeling.
  • Turn Red litmus papers Blue.
  • Produce Hydroxide ions when dissolved in H2


Ca(OH)2Arrow used In Chemical EquationCa2+      + 2OH

NH3   +  H2OArrow used In Chemical EquationNH4+   +   OH

  • All alkalis can react with acids to form a salt and water. This reaction is called neutralization. In this reaction the hydrogen ions from the acid and the hydroxide ions from the alkali react to form water.

NaOH  + HClArrow used In Chemical Equation NaCl  +   H2O

Ionic Equation:

H+    +    OHArrow used In Chemical Equation H2O

  • Alkalis when heated with ammonium salts give off ammonia gas.

Alkali + Ammonium SaltArrow used In Chemical EquationAmmonia     +  Water  + Salt

Ca(OH)2  + 2NH4C l Arrow used In Chemical EquationCaCl2    +  2H2O   + 2NH3


  • Alkalis can react with a solution of one metal salt to give metal hydroxide and another metal salt. The general equation for this reaction is:

Alkali + Salt (of Metal A)Arrow used In Chemical EquationMetal Hydoxide     + Salt (of Metal B)

  • The Metal OH  appears as a precipitate if it is insoluble in water.

2NaOH     +  Fe SO4Arrow used In Chemical EquationFe(OH)2     +    Na2SO4


Strong Alkalis:

Strong Alkali is that, which completely ionizes in solution.

NaOHArrow used In Chemical Equation Na+     +   OH

NH4Arrow used In Chemical Equation NH4+    +   OH


Weak Alkalis:

Weak Alkali is that, which partially ionizes in solution.


Ammonium Hydroxide (Ammonia gas dissolved in water).–   

NH4OHArrow used In Chemical Equation NH4+ +   OH


Distinguishing between weak and strong Alkali:

Stronger Alkali at the same concentration has higher pH.

At the same concentration, stronger alkali would be the best conductor of electricity.


Uses of Basis And Alkalis:

  • Ammonium Solution:
  • In window cleaning solution
  • In fertilizers

Calcium Oxide:

  • In neutralizing acidic soil.
  • To make Iron, Concrete and Cement.

Magnesium Hydroxide:

  • In toothpaste to neutralize acid on teeth.
  • In antacids, to relieve indigestion.

Sodium Hydroxide:

  • In making soaps and detergents.
  • Industrial – Cleaning detergents.


p H scale:

The p H scale is a set of numbers used to indicate whether a solution is acidic, neutral or alkaline.

p H Calculation:

Based on number of H ions and OH ions:

Strong Acids – Higher concentration of H ions.

Strong Alkalis – Higher concentration of OH ions.



Indicators for detecting Acids And Basis

Why is Soil pH important?

  • It affects the growth and development of plants.
  • Plants best grow when the soil is neutral or slightly acidic.
  • Plants will not grow in soil that is too acidic.
  • This can happen when too much fertilizer is added to the soil and due to acid rain.

Hence the pH value of soil should be between 5 and 9.

Controlling Acidity of Soil:

  • Chemicals are often added when soil becomes too acidic.
  • The soil is treated with bases such as:

Quick Lime (Calcium Oxide) CaO

Slaked Lime (Calcium Hydroxide) CaOH

Lime Stone (Calcium Carbonate) CaCO3

  • The basis react with the acids in the soil and raise the p H so that plants can grow healthily.

However adding too much base will make soil too much alkaline – thus making soil unsuitable for crop growth.



Oxides are compounds containing Oxygen.

Acidic Oxides:

  • Non Metals may form acidic oxides.
  • Most acidic oxides dissolve in water to form acids.
  • They do not react with acids but they react with alkalis to form a salt and water.


SO2 + H2OArrow used In Chemical EquationH2SO4 (Sulphurus Acid)

CO2 + H2OArrow used In Chemical Equation H2CO3 (Carbonic Acid)

SO3 + H2OArrow used In Chemical Equation H2SO4 (Sulphuric Acid)

Neutralization Reaction:

SO2 +  2NaOHArrow used In Chemical EquationNa2SO3 +   H2O

SiO2 +  2NaOHArrow used In Chemical Equation Na2SiO3 +   H2O

Basic Oxides:

  • The oxides of metal are basic oxides.
  • Most Basic Oxides are insoluble in water.
  • Those that are soluble are called alkalis ( Na2O)
  • Solid at room temperature.
  • React with acids to form a salt and water.
  • No reaction with bases or alkalis.
  • In soluble in bases.


CaO    + H20Arrow used In Chemical EquationCa(OH)2

CaO    + 2HNO3Arrow used In Chemical EquationCa(NO3)2    +  H20

Amphoteric  Oxides:

  • Metal Oxides that react with both acids and basis to form salt and water.
  • Oxides that contain both the abilities of acids and alkalis.
  • If atmospheric oxide is reacted with an acid it will show the properties of an alkali and a neutralization reaction occurs.
  • If it is reacted with an alkali – will shows acidic properties – a neutralization reaction occurs.
  • Showing reaction with both acids and base.
  • Oxides of Aluminum (Al), Zinc(Zn) and Lead(Pb).
  • Produce Salt and H2O when reacting with acid or alkali.


ZnO   +  2HClArrow used In Chemical EquationZnCl2  + H2O

ZnO    + 2NaOHArrow used In Chemical EquationNa2ZnO2   + H2O


Neutral Oxides:

  • Some Non – Metals form oxides, that show neither basic nor acidic properties.
  • Insoluble in Water.
  • Do not react with acids or basis.


  • Carbon Monoxide (CO)
  • Water   (H2O)
  • Nitric Oxide (NO)
  • Hydrogen Per Oxide (H202)

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