Any Chemist able to explain Washing Up Liquid to the layman?

Mad Mike

Can any chemist enlighten me about the ingredients of washing up liquid please?

In the supermarket the other day I was shopping for washing up liquid. Confronted with a range of brands and prices I examined the labels to try and figure out which was better value.

I don't remember the exact pricing but there seemed to be three tiers of products:

1. Fairy Liquid was on its own, the most expensive brand and also had the highest concentration of active ingredients:
15-30% Anionic Surfactants
5-15% Non-ionic Surfactants

2. The second tier had a variety of products from different manufacturers ranging from as little as half the price of Fairy to almost as expensive. They all had similar active ingredients:
5-15% Anionic Surfactants
Either no mention of Non-Ionic Surfactants or less than 5%

3. The third tier had some very cheap generic brands perhaps a quarter the price of Fairy. Their ingredients were:
Less than 5% Anionic Surfactants
Again no mention of Non Ionics.

I understand at a basic level that washing up liquid is a mixture of soap and water and it seems clear that the more expensive brands have higher concentrations of soap. What is the difference between anionic and non-ionic though and how come only Fairy seems to have non ionic? I did study chemistry for my leaving cert many years ago so I remember the difference between ionic and covalent bonds but even with the aid of Google I couldn't figure this out.

In use I can clearly see the difference between the very cheap brands and the mid range. The cheap stuff is very watery. I find it harder to see a difference between the mid range and Fairy though even though Fairy is supposedly twice as concentrated. Of course I generally just slobber in a good squirt of liquid so this is not a very scientific test.

Capt'n Midnight

washing up liquid usually doesn't have any soap. Many of them add a foaming agent to make bubbles because soapy water makes bubbles. We associate bubbles with clean because soap does both. For washing machine detergents an anti-foam is used because bubbles would be a bad thing.


Surfactants are molecules one end of which is hydrophobic and so likes oil/fat/grease, the other end is hydrophillic and so likes water. This means the oily dirt can be changed to an emulsion suspended in water.

The water loving hydrophilic part can have a positive or negative charge or be neutral.

https://en.wikipedia.org/wiki/Surfactant#Anionic - this lists some of the compounds that may be used, different recipes for different brands / jobs


Unfortunatley part of the reason for the ingrident list to be a bit vague is to prevent you making a direct comparison

Mad Mike

Thanks for the reply Cap'n Midnight.

OK so the surfactants have a head that bonds to water and a tail that bonds to grease. The "ionic bits" are the head that bonds to water. Anionic and non-ionic seem to be two different kinds of head bit.

Anyone know which is better and why Fairy is the only wup liquid that seems to have the non-ionic kind.

Edit: reading further it seems that anionic surfacants are all some kind of "ate" (sulphate, phosphate etc) while non ionic are likely to be some kind of alcohol.

dasanimal

the wikipedia link that capt gave you explains it pretty well.
Anionic surfactants had a negatively charged head, as opposed to a neutral charged head for nonionic surfactants.
Anionic surfactants may be better for attaching to dirt/compounds that is positivey charged whereas the nonionic surfactants can attach to neutral dirt/compounds.

So i would imagine the reason Fairy is better is because it contains more anionic and nonionic surfactants and therefore is able to bind to a greater variety of dirt/compounds??

I do know surfactants are often used to lower the hydrophobicity of materials to enable reactions to occur