Acids, Bases and Writing Chemical Equations

Definition of an acid:

An acid is a substance which produces hydrogen ions as the the only positive ions when it is dissolved in water. Acids are either classified as weak or strong.

Some common strong acids are:

Hydrochloric acid (HCl)
Nitric Acid (HNO3)

Sulfuric Acid (H2SO4)

A common weak acid is Ethanoic acid, or CH3COOH.

Weak acids dissociate partially in water but a strong acids dissociates completely in water.

Properties of Acids

An acid, when dissolved in water, forms a colorless solution. Solutions of acids have:

• A sour taste
• Change the color of pH indicators (e.g. Turns blue litmus paper red)
• React with hydrogen ions and conduct electricity
• React with metals, carbonates and bases.

Acid + Metal -> Salt + H2

e.g. 2HCl + Zn -> ZnCl2 + H2

Acid + Carbonate -> Salt + CO2 + H2O

e.g. H2SO4 + CaCO3 -> CaSO4 + CO2 + H2O

Acid + Base -> Salt + H2O

e.g. MgO + H2SO4 -> MgSO4 + H2O

Properties of bases

Bases are the oxides or hydroxides of metal that reacts with an acid to form a salt and water only. Most bases are insoluble in water, and the bases that are soluble in water are called alkalis. These alkalis produce hydroxide ions (OH-) in water. All alkalis are bases but not all bases are alkalis.

Alkalis have:

• A soapy feel and a bitter taste
• Can change the color of pH indicators (turn red litmus paper blue)
• Can react with acids
• Can react with ammonium salts to form salt, ammonia and water

Base + Ammonium Salt -> Salt + NH3 + H2O

e.g. NaOH + NH4Cl -> NaCl + NH3 + H2O

• Can react with a solution of one metal salt to give metal hydroxide and another metal salt

Base + Metal Salt -> Metal Hydroxide + Another metal salt

e.g. CuSO4 + 2NaOH -> Cu(OH)2 + Na2SO4

Types of oxides:

1. Acidic Oxide
2. Basic Oxide
3. Neutral Oxide
4. Amphoteric Oxide

Acidic Oxide

An acidic oxide is a non-metallic oxide that neutralizes a base to form salt and water only. It reacts with water slightly to form an acid solution.

Basic Oxide

A basic oxide is a metallic oxide that neutralises with an acid to form salt and water only. If it is soluble in water, it forms an alkali.

Neutral Oxide

Neutral oxides are non-metallic oxides that have neither acidic nor basic properties. They are insoluble in water and do not react with water.

Amphoteric Oxide

Amphoteric oxides are metallic oxides that react with both acid and base to form salt and water. They have both acidic and basic properties.

Alkalis can be weak or strong. When strong alkalis dissolve in water, they become OH- ions in the solution.

Strong alkalis dissociates completely in water while weak alkalis dissociate partially in water.