Self Assess 5.2 – Chemistry Form 5 Chapter 5


Question 1:
What is soap?

Answer:
Soaps are sodium or potassium salts of fatty acids.


Question 2:
What is detergent?

Answer:
Detergents are sodium or potassium salts of sulphonic acids.


Question 3:
Name the process of soap preparation.

Answer:
Saponification.


Question 4:
Give a balanced chemical equation for the reaction between stearic acid and sodium hydroxide to prepare soap.

Answer:
$$ \mathrm{CH}_3\left(\mathrm{CH}_2\right)_{16} \mathrm{COOH}+\mathrm{NaOH} \rightarrow \mathrm{CH}_3\left(\mathrm{CH}_2\right)_{16} \mathrm{COONa}+\mathrm{H}_2 \mathrm{O} $$

Question 5:
State the two stages in the process of preparing detergents.

Answer:
Sulphonation or sulphation and neutralisation.


Question 6:
One of the properties of soap or detergent is to form foam. What is the function of the foam?

Answer:
Soap bubbles will lower the surface tension of water surface in the following ways:

• Soap bubbles are a layer of spherical soap film that covers air or gas.

• The film consists of a thin layer of water trapped between two layers of soap molecules. 

• The hydrophilic part of the soap molecule will dissolve in water, while the hydrophobic hydrocarbon chain part tends to avoid water.

• The hydrophobic ends of soap molecules accumulate on the surface, avoiding water and stays away from the water molecular layer.

• As a result, water molecules separate from each other. Increased distances between water molecules will cause a decrease in surface tension, which allows bubbles to form. Thus, soap can wet the surface of the fabric.