想問有關cleansing agent

The cleansing effect of acids and alkalis are NOT based on their corrosive properties.

There are two common usages of using household cleansing agents:

The first usage is to remove oil/grease. Alkalis are better than acids in this aspect. The hydrolysis of oil/grease in alkali is call saponification. In saponification, oil/grease is changed to soap, which is more soluble in water than oil/grease. Furthermore, the soap formed can further remove the unreacted oil/grease by emulsification. An example of saponification of oil/grease is shown below.

圖片參考：http://z.about.com/d/chemistry/1/0/i/soap.gif

Acids can also be used to remove oil/grease, but are less effective than alkalis. This is because the hydrolysis of oil/grease is reversible in acidic solution, but is irreversible in alkaline solution.
Kitchen cleansers are mainly used to remove oil/grease. Therefore, kitchen cleansers usually contain strong alkalis.

The second usage is to remove rust. Only acids can remove rust (Fe2O3•nH2O).
Fe2O3•nH2O(s) + 6H+(aq) → 2Fe3+(aq) + (n+3)H2O(l)
The old toilet drain pipes are made of iron. Rust formed inside the drain pipes can be removed by acids. Therefore, the toilet cleansers usually contain strong acids.

2008-05-30 21:50:21 補充：
參考賌料：
http://z.about.com/d/chemistry/1/0/i/soap.gif