Other ingredients (2 of 2)
PEG-2 hydrogenated tallow ammonium chloride and tallowtrimonium chloride are cationic detergents. They are based on quaternary ammonium compounds and have structures like the one in Figure 5.
Figure 5: A quaternary ammonium compound surfactant
The ionic head mixes with water while the hydrocarbon tail is non-polar. Cationic surfactants can be used in acid solution.
Anionic surfactants such as soaps like the one in Figure 6 cannot be used in acid solutions because the hydrogen ions in the solution would react with the negative ions and protonate them. This produces a non-ionic and therefore insoluble compound
Figure 6: An anionic surfactant
Laureth-10, Figure 7, is a non-ionic surfactant based on the group -(CH2CH2O)n-. It is relatively polar with a non-polar hydrocarbon tail.
Figure 7: A polyethylene ethoxylate - a non-ionic detergent
Non-ionic surfactants can also be used in acid solutions.
A further function of the tallow ammonium chloride is that it acts as a thickening agent so that the product will cling to the sides of the toilet pan and remain effective through many flushes. Harpic also contains a blue colouring agent so that the user can see clearly where the product is and can make sure that the whole of the toilet rim is covered, a task that would be more difficult with a colourless liquid.
The acid in Harpic means that it is an effective germicide, killing ‘99.9% of germs’.
a) Identify the functional group of the anionic surfactant in Figure 6.
b) Write an equation to show the protonation of this group.
a) Carboxylic acid (the sodium salt of a carboxylic acid) COO-.
b) RCOO- + H+ → RCOOH