Oftentimes when people hear that something has a low or high pH, they worry that it is dangerous. But this is not the case, pH alone cannot tell you if a substance is dangerous or not. Anyway, bases are typically considered more dangerous than acids! But what is pH? A substances pH is simply the concentration of hydrogen ions (H+) of the material when in solution (usually water). It is a numeric (logarithmic) scale used to specify how acidic or basic an aqueous solution is and an aqueous solution is just a solution where water is the solvent.  

Now you might be wondering, what makes an aqueous (aq.) solution acidic or basic? Essentially, acids have more hydrogen ions (H+) than pure water and bases have less hydrogen ions than pure water. This is because an acid will release a hydrogen ion into an aq. solution, while a base will release a hydroxide ion (OH-) – by accepting the hydrogen ion. Did you know that this also makes them taste different? Not that you should try it, but if you taste an acid it will taste sour (like lemon juice) and a base will taste bitter (like milk of magnesia).

A substance’s pH is a measure of concentration of hydrogen ions, not of strength. When talking about acids and bases, strength has a very technical meaning. With weak acids, only a certain percentage can act as an acid and with a strong acid, all of it can act as an acid (and the same for bases). So yes, a strong acid or a strong base will be better at dissolving substances than a weak acid or weak base. But when referring to the strength of an acid/base as strong or weak, scientists are typically not referring to the pH of the aq. solution or how caustic/corrosive it is. They are referring to its ability to ionize (produce hydrogen or hydroxide ions) in water, its ability to act as an acid/base. This is important to remember because acids/bases with a pH closer to 7 (like pure water) are not necessarily safer. A good example is hydrofluoric (HF) acid. In terms of pH hydrofluoric acid is considered a weak acid – it does not fully ionize in water – but it is extremely dangerous because of how corrosive it is.

Now keeping all that in mind, let’s look at some average pH values for common substances:

• Liquid Drain Cleaner: pH = 14
• Bleaches, Lye: pH = 13.5
• Ammonia Solutions: pH = 11.5-10.5
• Baking Soda: pH = 9.5
• Sea Water: pH = 8
• Blood: pH = 7.4
• Pure Water: pH = 7
• Milk, Saliva: pH = 6.6-6.3
• Black Coffee: pH = 5
• Soda: pH = 3.5-2.5
• Stomach acid: pH = 3.5-1.5
• Concentrated (100M) HF: pH = 2.1
• Lemon Juice, Vinegar: pH = 2
• Battery Acid, Hydrochloric Acid: pH = 0
  
  

Take note of the pH of lemon juice and vinegar, it is only 2, but you don’t think of them as dangerous do you? So before you judge a substance by its pH, take a moment to investigate how corrosive or caustic it is. A substance’s pH won’t necessarily tell you how dangerous it is, but how corrosive or caustic it is will!

I would imagine that people – perhaps even you – who use disinfectants hear the word “quats” quite frequently. But do you know what quats are?

“Quats” is short for quaternary ammonium compounds, which are similar to ammonium ions in structure. Just instead of being 4 hydrogens surrounding 1 nitrogen, they have 4 R groups. Now these R groups can be many different things, but still be a quaternary ammonium compound. They can either be an alkyl group, which is a chain of carbons and hydrogens or they can be an aryl group, which is a ring of carbons and hydrogens. These chains and rings can also contain other molecules, such as oxygen.

Different quats have different functions because of the variety of R groups that they can have. The different combinations of rings, chains, carbons, hydrogens, and other elements give each quat its own functionality. This is why there are so many quats that are used in cleaners and disinfectants. Quats tend to have antimicrobial properties, making them valuable as disinfectants. They work in a variety of ways to disrupt cell membranes, inactivate energy-producing enzymes, or denature essential proteins in the microbes, effectively killing them.

The problem is that quats also have the potential to add to the growing number of resistant bacteria and they make poor cleaners. When a quat-based disinfectant is used to clean, some of the quats get left behind on the surface as a residue. This residue builds up on the surface, causing it to look dull and grimy. Over time this accumulated grime will make the surface look dirty even after being cleaned and it will attract even more dirt to it! So the various microbes may be dead, but the surface will look dirty, and who wants that?

Lastly, if you ever wonder about the really long names that quats have, it is just a way for chemists to remember the structure of the molecule. By breaking down the name, they can easily draw out the molecule’s structure and from that know how it will behave!

If you find this information useful and want to know more, let us know in the comments!