Friday 19 May 2017

Bases

Bases:

Bases are metal oxides and metal Hydroxides.
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

Alkali:

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)

Properties:
  • Alkalis have bitter taste and soapy feeling.
  • Turn Red litmus papers Blue.
  • Produce Hydroxide ions when dissolved in H2
e.g.
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+    +    OH– Arrow 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.
Example:
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:

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:

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.
Examples:
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 EquationNa2SO+   H2O
SiO2 +  2NaOHArrow used In Chemical Equation Na2SiO+   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.
Examples:
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.
Example:
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.
Examples:
  • Carbon Monoxide (CO)
  • Water   (H2O)
  • Nitric Oxide (NO)
  • Hydrogen Per Oxide (H202)

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