pHacts about pH

There is always a lot of confusion when using or selecting from the wide variety of chemicals in the car care industry regarding what pH actually is, and how it affects the chemicals we use and the surfaces we use them on; so we thought it could be useful to put together a brief guide on what it is, what it means and why it is relevant to what we do. We cover the topic in far greater depth in our Career Development courses, but this is a useful brief read for anyone looking to get a better understanding on the subject and work safely!

What is pH?

“pH is the negative of the base 10 logarithms of the activity of the H⁺ ion within a solution.”

Not very helpful without a chemistry background, so we’ll expand on that below to make sense if it – but the scale was invented by the director of the chemical department at the Carlsberg Laboratory in 1909 as precise way to measure hydrogen ion concentration while studying proteins and improving the beer brewing process, and is an abbreviation for “potential of Hydrogen” – crucially, in water-based solutions.

The more free hydrogen ions (H+) present in a solution, the higher the acidity, which results in a lower pH number. If a solution has few free hydrogen ions, it gets a higher number to represent an Alkaline or Base solution

It sounds much simpler than it is, as there were few methods for accurately counting these ions before. It is found by counting the number of positive hydrogen ions it contains, and then doing some maths to equate it onto the scale.  The actual base calculation and placing on the scale is done in the laboratory, and they will share that nugget of information which we can then find (when relevant) on the Safety Data Sheet of whichever product we are looking at.

The “in water based solutions” part of the definition is important, as you can’t have a dry acid or alkaline. You can have powders, which when dissolved in water become strong chemicals, but without water, you do not have pH. If you left a chemical on a surface in the sun, the pH will get stronger as the water evaporates, but once dry it no longer exists on the pH scale, just like petrol or… sand. Both of these can do damage, but it’s not the damage of a strong pH.

The logarithmic bit relates to how the scale represents the n0minal “strength” of the chemical. Twice as strong does not mean it bumps up to the next number on the scale – it needs to increase (concentrate) or  decrease (dilute) by a factor of 10 – so to move down from pH1 to pH2 it needs to be diluted to a tenth of its original amount with a neutral substance. To go from pH1 to pH 3 – it needs to be 100 times less acidic through neutralisation and/or dilution.

How do you tell an acid from an alkali?

pH is measured on a scale from (near) 0 to 14, with 7 (neutral) being in the middle and denoting those substances which are neither acidic nor alkaline. A simple way to remember which falls at which end of the scale is to look at the number of letters in the words: “Acid” has very few letters and “Alkaline” has loads – the lower the pH value, the more acidic it is! You can use litmus paper for a visual gauge, but for an accurate decimal number you need a pH meter. These are cheap and readily available, so if you’re unsure if something has been diluted you can do a quick test to compare it to the material’s Safety Data Sheet.

A solution can be higher Alkaline than pH 14, or more acidic than pH zero, such as Fluoroantimonic acid – a “super-acid”, but they wouldn’t appear represented on the pH scale, as no water is present at these extremes (remember, “potential of Hydrogen in water”) There is a different scale capable of measuring these called the Hammett acidity scale, but it’s not relevant to this industry.

Why does pH matter in detailing?

Different substances will be better or worse at achieving different outcomes on a surface.  In our case, certain products may need to be chosen to deal with particular types of contamination which we are trying to remove from the surface of a vehicle.

The ability to identify the right chemical to use in a particular situation will make us more efficient, reduce waste and limit the potential for harm that could be caused by repeated applications of an incorrect product.

In very general terms;

Alkaline products are good organic degreasers – think Shampoos, Snowfoams, All Purpose Cleaners for removing oily road film, grease and the oils from your skin.

Acids will dissolve inorganic surface deposits – think Wheel cleaners (brake dust) Iron Fallout Remover (…iron), Waterspot remover (calcium deposits)

Does this mean that a high or low pH is necessarily going to cause damage or is unable to affect the opposite contamination? No! –  pH is not (necessarily) a measurement of aggression or capability, and it will depend on a variety of factors to determine its effect on a substrate, including concentration, heat, and reactivity, as well as other ingredients in the product’s makeup.

It also does not render pH neutral as useless or “mild”. There are many ways to achieve contaminant removal through alcohol, sugar based surfactants, or even just targeted chemistry. Alkaline wheel cleaners can be effective at removing brake dust, and acidic cleaners can degrease well. The general terms are there as overall guidance, not as absolutes.

There are so many caveats when talking about pH levels and the affect they can have. pH is a great first indicator as to the intensity or risk with a product, but it is by no means an absolute.

Oxalic acid, for example, sits around pH 1, yet it’s commonly used in fallout removers marketed as “safe on all surfaces” – this is because at the tested dilution and application it works within safe limits, not because a low pH automatically means danger.

By contrast, a concentrated wheel cleaner using phosphoric or hydrochloric acid for example – both highly reactive acids – at pH1 may need considerable dilution to bring their concentration down to safe working levels, so reading the instructions closely matters – you want to be sure you’re applying it exactly as it was tested for use. Dilution accuracy, surface assessment, and common sense all play a role here.

The presence of an acid or alkaline doesn’t make a chemical inherently dangerous. Phosphoric acid can be a dangerously aggressive and damaging surface cleaner, if improperly diluted, but you also drink it whenever you have a Coke.

Don’t be afraid of using strong pH chemicals from reputable companies if needed, and appropriate. They SHOULD have been tested for surface compatibility for the purpose intended, and carry all necessary instructions. However, do be aware that the higher up or down the scale you go, the more trust you are putting into the manufacturers to get it right for every scenario and situation – so don’t be averse to testing for reaction before use.

The manufacturer may get the blame, but you’ll still get the bill…

Getting to grips with chemical selection and safety is a big part of our Career Development courses – and if you’d like to go deeper on picking the right products in the first place, our guide to choosing detailing products as a professional is the natural next read.