Page 116 - Chemistry_Form_2

Chemistry
for Secondary Schools

FOR ONLINE READING ONLY

Figure 5.7: Red litmus paper immersed in an alkali solution

3. Bases change the colour of phenolphthalein (POP) indicator pink and that of
methyl orange (MO) indicator yellow.

4. Soluble bases react with most cations to precipitate hydroxides. In this case,
they precipitate insoluble metal hydroxides from their salt solutions. For
example, potassium hydroxide reacts with iron(III) chloride to yield iron(III)
hydroxide and potassium chloride.

Ionically, the reaction is represented as:

5. Bases react with acids to form salt and water. For example, sodium hydroxide
reacts with dilute hydrochloric acid to produce sodium chloride and water.

The ionic equation is

6. Alkalis react with ammonium salts to produce ammonia gas.

Strengths of bases
The strength of a base or alkali is its ability to ionise in aqueous solution to
produce hydroxide ions . Like acids, the strength of a solution of a base
can be determined by the pH value of that particular solution. The more the base
ionises in aqueous solution, the stronger it is. Alkalis are strong bases because
they ionise completely in aqueous solutions to produce free ions. Examples of
strong bases are potassium hydroxide (KOH) and sodium hydroxide (NaOH).

Student’s Book Form Two 109

01/08/2025 11:21:03
CHEMISTRY FORM TWO NEW 2025 DUMMY.indd 109 01/08/2025 11:21:03
CHEMISTRY FORM TWO NEW 2025 DUMMY.indd 109