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Acids, alkalis and salts

In this chapter you will learn:

  1. Acids and alkalis

  2. Reactions of acids

  3. What is neutralisation reactions?

  4. Strong and weak acids

  5. pH of acids and alkalies

  6. Neutralisation of acids and salt production

Acids and alkalis

  • An acid is a substance that produces Hydrogen ions (H+) in water.

  • Acid Turns blue litmus paper red.

  • Acidic solutions have pH values less than 7.

  • These are 7 strong acids: chloric acid, hydrobromic acid, hydrochloric acid, hydroiodic acid, nitric acid, perchloric acid, and sulfuric acid.

  • Strong acids completely dissociate into ions in water.

  • Weak acids only partially dissociate.

  • The pH scale is used to measure a solution is acidic, neutral, or alkalinie.

  • Acid-alkali indicators are used to determine if a solution is acidic, neutral (pH 7) or alkaline. Three acid-alkali indicators are: Litmus paper, Methyl orange and Phenolphthalein.

  • A substance that reacts with an acid to form a salt and water is called a base.


  • A base that is soluble in water is called alkali.

  • Alkalis are substances that produce Hydroxide ions (OH-) in water.

  • Alkalis are sources of hydroxide ions, OH-.

  • We can find the pH of any solution using universal indicator.

  • Alkaline solutions have pH values more than 7.

  • Alkaline solutions turns red litmus blue.

  • The pH of a neutral solution is 7.

Reactions of acids

The following table shows reactions of acids and their products:

Reactions with metals A salt and hydrogen
Reactions with metal oxides A salt and water
Reactions with metal hydroxides A salt and water
Reactions with carbonates A salt, water and carbon dioxide

Neutralisation reactions

  • A neutralisation reaction is a reaction between an acid and a base.

  • In acid-alkali neutralisation reactions, hydrogen ions from the acid react with hydroxide ions from the alkali to produce water.

Strong and weak acids

  • Acids are source of hydrogen ions in a solution.

  • In a solution, acid dissociates or breaks down to form ions.

  • Strong acids dissociate completely into ions in solution.

  • Weak acids dissociate only partially into ions in solution.

pH of acids and alkalies

  • The pH of a solution is a measure of its concentration of hydrogen ions.

  • The higher the concentration of H+ ions in an acidic solution, the lower the pH.

  • The higher the concentration of OH- ions in an alkaline solution, the higher the pH.

Neutralisation of acids and salt production

  • Acids are neutralised by alkalis and bases to produce salts and water, and by metal carbonates to produce salts, water and carbon dioxide.
  • The particular salt produced in any reaction between an acid and a base or alkali depends on the acid used.
  • hydrochloric acid produces chloride salts.
  • nitric acid produces nitrate salts.
  • sulfuric acid produces sulfate salts.
  • Soluble salts can be made from acids by reacting them with solid insoluble substances, such as metals, metal oxides, hydroxides or carbonates.
  • During the Preparation of soluble salts, the insoluble reactant is added in excess to ensure that all of the acid has reacted.The excess reactant is then removed by filtration to ensure that only the salt and water remain.