TOGWT: Using pH values to select car care products

Potential hydrogen [: in chemistry, pH is a measure of the activity of the (solvated) hydrogen ion. p[H], which measures the hydrogen ion concentration is closely related to, and is often written as, pH .Pure water has a pH very close to 7 at 25°C. Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline] [1]

Simply put the potential of hydrogen (pH) scale is a set of numbers between 0 and 14 where 0 (Hydrochloric acid) is the most acidic and 14 (Bleach or Lye) is the most alkaline (caustic) pH is a characteristic of water solutions only; without water, you cannot have a pH. The pH scale is logarithmic; for every integer that the scale decreases the material is 10 times more acidic.

Why pH values is not an ideal criteria for the selection of car care products

One of the most confusing things about this business is the chemicals used and the chemistry behind them. Certain product or combination of products can have a negative impact and to the newcomer in the industry, or your everyday enthusiast, understanding the chemical interactions could become challenging, if not darn right confusing. As a Chemical Engineer I have a gained a lot of knowledge on chemicals but I can't imagine being relatively new to the industry and coming into detailing today.

Product vendors are in business to sell products and sometimes rename the same product to do other things i.e. a swirl removing polish vs. a finishing polish (they both do the same job) However with chemicals it’s not quite that simple

Testing the pH

The term pH is a measurement of the relationship between hydrogen ions and hydroxyl ions. When you have more hydrogen ions than hydroxyl ions, you have an acid. Likewise, if you have more hydroxyl ions than hydrogen ions you have a base (alkali).

The pH scale is a measure of the acidity or basicity (Alkali) of a solution. It is approximates but is not equal to p [H], the negative logarithm base 10) Base (Acid) 1-7, Alkaline 7- 14; the pH of a solution is temperature-dependent.

Unfortunately the pH scale is logarithmic; for every integer that the scale decreases the material is 10 times more acidic. Those of us in earthquake country know all too well the consequences of a change of from 6 to 7 on the logarithmic, Richter scale. The difference in the pH scale is just as dramatic and therefore just as misleading.

A substance that is neither acidic nor basic is neutral; pure water has a neutral pH of 7.0 each whole pH value below 7 is ten times more acidic than the next higher value. For example, a pH of 4 is ten times more acidic than a pH of 5 and 100 times (10 times 10) more acidic than a pH of 6. The same holds true for pH values above 7, each of which is ten times more alkaline than the next lower whole value. For example, a pH of 10 is ten times more alkaline than a pH of 9.0

Acidic and basic are two extremes that describe the chemical properties of a chemical. Mixing acids and bases can cancel out or neutralize their extreme effects. A substance that is neither acidic nor basic is neutral. The pH of distilled water is 7, this is neutral. Any solution with a pH below 7 is an acid and any solution with a pH above 7 is a base (alkali).

Surfactants perform other important functions in cleaning, such as loosening, emulsifying (dispersing in water) and holding soil in suspension until it can be rinsed away. Surfactants can also provide alkalinity, which is useful in removing acidic soils. Surfactants are classified by their ionic (electrical charge) properties in water: anionic (negative charge), non-ionic (no charge), cationic (positive charge) and amphoteric (either positive or negative charge).

Soap is an anionic surfactant. Other anionic as well as non-ionic surfactants are the main ingredients in today's detergents. The chemistry of surfactants- soaps are water-soluble sodium or potassium salts of fatty acids. Soaps are made from fats and oils, or their fatty acids

Although soap is a good cleaning agent, its effectiveness is reduced when used in hard water. Hardness in water is caused by the presence of mineral salts - mostly those of calcium (Ca ²⁺) and magnesium (Mg²⁺), but also sometimes ferrous irons (Fe) and manganese (Mn). The mineral salts react with soap to form an insoluble precipitate known as soap film or scum. Soap film does not rinse away easily. It tends to remain behind and produces visible deposits on clothing and makes fabrics feel stiff. It also attaches to the insides of bathtubs, sinks and washing machines.

In practical applications, a formulator can get identical pH values by using various quantities of different acids. For example very small amounts of very strong acids or larger amounts of weaker acids can result in the same pH. The addition of a molecule of water to a chemical compound, without forming any other products is known as hydration (i.e. dilution causes the pH to decrease) But since pH is not a very good indicator of the strength of the acid in every system, this approach won't always produce the desired results. Each acid has properties that make it most useful for certain jobs. For example Citric acid is quite good at picking up Calcium ions in solution so acts as a good water softener where the same pH of a Sulphuric acid solution would be worthless for that application.

My point here is that, it is not possible to judge how well a product will do the job it is designed for just by measuring the pH, and stronger is not always better. So, acid strength is always relative to the system you’re measuring and what materials are in danger of being dissolved or attacked by the acid pH is a measure of the relative strength of an acid but the key word is relative.

I think this illustrates the importance of detailers understanding the ‘science’ of cleaning; and to this end it is helpful to have a basic knowledge of soap and detergent chemistry and what is needed to achieve effective cleaning

Some terms used to describe acids or basic

Neutralisation - a chemical reaction whereby an acid and a base react to form water and a salt; generally, the following occurs: acid + base → salt + water. Neutralization reactions are exothermic; causing agitation and giving out heat to the surroundings

Balanced pH - or neutral pH

Controlling pH - popular chemicals include calcium carbonate, calcium oxide, magnesium hydroxide, and sodium bicarbonate. The selection of an appropriate neutralization chemical depends on the particular application. pH controlled means it follows the major automotive manufacturer’s guidelines for exterior cleaners; the control limit being a pH 10.0<

Acids, Bases, and pH

There are several ways to define acids and bases, but pH only refers to hydrogen ion concentration and is only meaningful when applied to aqueous (water-based) solutions. When water dissociates it yields a hydrogen ion and a hydroxide.

Pure water is said to be neutral, with a pH close to 7.0 at 25 °C (77 °F). Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are said to be basic or alkaline.

An alkaline cleaner (hand soap has a pH of between 9.0 – 10.0) is used to clean most materials used in an automobile interior, including finished leather (leather is acidic by nature). Cleaning products use surfactants and other additives (such as water softeners) so its pH is not the only criteria used (i.e. a neutralized acid wheel cleaner has a pH of 7.0, so if pH is the only criteria it should be safe to use this product on anything as pH 7 (neutral)

Another reason for non-reliance of pH values when selecting products is the use of a buffer solution , this is an aqueous solution consisting of a mixture of a weak acid and its conjugate base or a weak base and its conjugate acid, Citric acid is a useful component of a buffer mixture. It has the property that the pH of the solution changes very little when a small amount of strong acid or base (alkali) is added to it.

Buffer solutions are used as a means of keeping pH at a nearly constant value in a wide variety of chemical applications.

Sodium hydroxide is often used for this purpose Dissolution of sodium hydroxide is highly exothermic, and the resulting heat may cause heat burns or ignite flammables. It also produces heat when reacted with acids.

The main priority is to ascertain the material you are trying to clean and then select a chemical that is compatible to clean it with Providing the cleaning product selected is suitable, apply product to an applicator not the area to be cleaned (the only exception to this is glass surface cleaning) apply several drops of the selected cleaning solution in an inconspicuous area and rub gently with a clean, white micro fibre towel. Do not over wet. Use small amounts of the product and blot frequently, do not rub or use too much pressure. Do not use the product if it adversely changes the material’s colour or texture.

Information resource

1. Wikipedia -http://en.wikipedia.org/wiki/Hydrofluoric_acid

2. Index to Hyper Physics- pH as a Measure of Acid and Base Properties

3. Material Data Sheet - MSDS - http://www.jtbaker.com/msds/englishhtml/H3880.htm

4. Conceptual Physical Science - Hewitt, Paul, Suchocki, J. and Hewitt, L. Addison-Wesley, 1999

5. Structural Inorganic Chemistry, A. F. Wells1984.

1. Detailing Chemicals Identification - http://www.autopia.org/forum/autopia-detailing-wiki/138479-detailing-chemicals-identification.html

2. Solvents used in detailing products - http://www.autopia.org/forum/guide-detailing/136837-solvents-used-detailing-products.html#post1451134

I would like to think that these articles become an asset to anyone who is new to detailing and to professionals alike, as well as industry experts who seek to advance their knowledge.

I hope the above article was informative. By having some understanding of the ‘What’ and ‘Why’ as well as the ‘How’ along with a little science to help you understand how the chemicals we use react, you can achieve the results you desire.

I would appreciate it if you would share this article as it helps other detailers further their knowledge.

Questions and/ or constructive comments are always appreciated.

TOGWT

Monday 27 April 2015

Using pH values to select car care products

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