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:

• 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 + AcidSalt + Water

CuO  +  H₂SO₄ CuSO₄  + H₂O

Neutralization Reaction:

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

Acid + BaseMetal 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   + H₂O2NaOH

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)₂Ca²⁺      + 2OH^–

NH₃   +  H₂ONH₄⁺   +   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  + HCl NaCl  +   H₂O

Ionic Equation:

H⁺    +    OH^–  H₂O

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

Alkali + Ammonium SaltAmmonia     +  Water  + Salt

Ca(OH)₂  + 2NH₄C l CaCl₂    +  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)Metal Hydoxide     + Salt (of Metal B)

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

2NaOH     +  Fe SO₄Fe(OH)₂     +    Na₂SO₄

Strong Alkalis:

Strong Alkali is that, which completely ionizes in solution.

NaOH Na⁺     +   OH^–

NH₄ NH₄⁺    +   OH^–

Weak Alkalis:

Weak Alkali is that, which partially ionizes in solution.

Example:

Ammonium Hydroxide (Ammonia gas dissolved in water).^–   

NH₄OH 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:

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 + H₂OH₂SO₄ (Sulphurus Acid)

CO₂ + H₂O H₂CO₃ (Carbonic Acid)

SO₃ + H₂O H₂SO₄ (Sulphuric Acid)

Neutralization Reaction:

SO₂ +  2NaOHNa₂SO₃ +   H₂O

SiO₂ +  2NaOH 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.

Examples:

CaO    + H₂0Ca(OH)₂

CaO    + 2HNO₃Ca(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   +  2HClZnCl₂  + H₂O

ZnO    + 2NaOHNa₂ZnO₂   + 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)