Chemistry in your cupboard

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’.