Potential of Hydrogen (pH) - by Jon Miller PhD [Chemical Engineering]
Potential of Hydrogen
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]
Simply put the potential of hydrogen (pH) scale is a set of numbers between 0 and 14 where 0 (battery fluid) is the most acidic and 14 (lye) is the most alkaline (caustic) pH is a characteristic of water solutions only. There must be water present to have a pH.
Unfortunately the scale is logarithmic, for every integer that the scale decreases the material is 10 times stronger. 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.
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.
pH is a scale of measurement of the relationship between hydrogen and hydroxyl ions, to determine if the material is neutral, basic (alkaline) or acidic (reactive), if there are more hydrogen than hydroxyl ions you have an acid the reverse will give you an alkali (another way to say basic]
Pure water is said to be neutral. The pH for pure water at 25 °C (77 °F) is close to 7.0. 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. Each whole pH value below 7 is ten times more acidic than the next higher value.
Alkalinity and pH
Are distinctly different from each other, although their definitions and functions can be easily confused; alkalinity is essentially a measurement of water's ability to neutralize acids. It is a measure of the buffering capacity of a system while pH is basically the measurement of the concentration of hydrogen ions in water, in terms of acidity or alkalinity.
Acidic and basic
Two extremes that describe chemicals just like hot and cold are two extremes that describe temperature. Mixing acids and bases can cancel out their extreme effects; much like mixing hot and cold water can even out the water temperature. Chemicals that are very basic or very acidic are called "reactive." A very common application of hydrochloric acid is to regulate the alkalinity (pH) of solutions.
These chemicals can cause severe burns. Automobile battery acid is an acidic chemical that is reactive, automobile batteries contain a stronger form of some of the same acid that is in acid rain. Household drain cleaners often contain lye, a very alkaline chemical that is reactive
pH is calculated using the following formula:
pH = -log10[H+]
pOH is calculated using the following formula:
pOH = -log10[OH-]
0.0–1.0 Strong acid Hydrochloric acid
1.0-2.9 Acidic Citric acid (lemon)
3.0-4.9 Weak Acid Vinegar (Acetic acid)
Oxalic 5.0-6.5 Very weak acid, Acid rain
6-7.3 Neutral Distilled water
7.3-9.0 Very weak alkali
9.1-10.9 Car wash concentrates
11.0-12.9 Weak alkali Baking soda, Seawater
13.0-14.0 Alkaline Bleach, Ammonia
Strong alkali Sodium Hydroxide (Lye)
A few examples of maximum acid strength might be helpful:
3.5-4.0. Acid rain has a pH of 3.5-4.0.
3.0-4.5 Bird excrement contain highly acidic concentrates of uric acid
7.75 to 8.25 Sea water
5.5 to 6.5 Tap water
Citric acid, found in citrus fruits has a pH of 2.0
Oxalic acid, found in spinach has a pH of 1.8
Vinegar has a pH of 2.0
‘Weak’ mineral acids Hydrofluoric acid has a pH of 3.14 Phosphoric acid has pH of 2.2
‘Strong’ mineral acids Hydrochloric acid, aka Muriatic acid has a pH of 0.1 @ 1N (indicates concentration) Sulphuric acid, battery acid, has a pH of 0 .32 @ 1N
A couple of things to note from this list are
a) how very strong "strong acids" are
b) How relatively weak yet dangerous hydrofluoric acid is and
c) And how small and misleading the difference is between organic acids and weak mineral acids. As an example, hydrofluoric acid (HF), one of the most highly regulated, most dangerous acids and the only acid that will dissolve glass is a weak acid. Also, these numbers are maximums, the pH increases when the solution is diluted or changes when there are other substances are dissolved in the solution.
Just to complicate things a bit more, mixing some strong mineral acids together with other relatively weak acids can create a solution of "super acid". This can result in acid strengths of up to 12 times higher than either acid by itself and are not measured accurately by the normal pH scale. In theory, this is the result obtained by adding HF to other mineral acids in wheel cleaners. Or mixing several weak acids together can have a synergistic effect where together these acids do more than just strong solutions of each one separately.
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. 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.
Ways to determine pH values -
· Litmus Paper - acidic, the paper will turn red, alkaline, the paper turns blue.
· Electronic pH Meters - Provide an accurate quantitative reading
· It is sometimes listed on a chemicals material data sheet (MSDS)
Corrosion and pH
There is one other factor relative to pH that needs to be explained, and it has to do with the corrosiveness of a compound. Both acids and alkali's have the capability of being corrosive, although one would have a pH range of 0 (acid), while the other would range in the area of 14 (alkali). Sodium hydroxide, a very strong and corrosive alkali would have the same damaging effect on human tissue as sulphuric acid. If a 25% concentration of sulphuric acid and phosphoric acid were measured for pH, both would range in the area of 0.
However, if sulphuric acid were allowed to contact human tissue, severe burns would result, while the average person would not detect even a burning sensation from contact with the phosphoric acid.
Why? The answer lies in the corrosive nature of some acids over others. Certain characteristics have been observed in the reactions of acids and alkalis, and were assigned classifications accordingly.
One of the classifications is corrosiveness. Therefore to classify a product or compound as being corrosive means that it would have the potential to erode materials, in some cases very rapidly, and it would have the capability of being harmful to objects such as structural components of a vehicle and human tissue. It is important to understand that some cleaning products are corrosive by their very nature and should be handled according to the directions on the container. All corrosive products are labelled as such and must follow strict government guidelines. (See also Alkalinity, Acid and pH)
As a chemical Engineer I would like to help detailers reach an intelligent and logical understanding of the many chemicals used in detailing. Improperly used chemicals can cause damage to the surface they are applied to (sometimes irreparably) because the detailer was not educated regarding the chemical make-up of the products they used.
Conversely I also want to show you that it's a waste of time to dedicate too much time and attention to them. All that is required is that you learn some basic chemistry i.e. what pH values mean, and what detailing chemicals to avoid or the precaution to take if you do choose to use them.
Material data sheets (MSDS)
Material Safety Data Sheet (MSDS) is required under the OSHA Hazard Communication Standard. The MSDS is a detailed informational document prepared by the manufacturer or importer of a hazardous chemical. It describes the physical and chemical properties of the product. MSDS’s contain useful information such as flash point, toxicity, procedures for spills and leaks, and storage guidelines.
Information included in a Material Safety Data Sheet aids in the selection of safe products, helps you understand the potential health and physical hazards of a chemical and describes how to respond effectively to exposure situations. Although there is an effort currently underway to standardize MSDS’s the quality of individual MSDS’s vary. A MSDS may be useful but it cannot substitute for prudent practices and comprehensive risk management.
An MSDS should be available for every chemical you use. Read these and follow the recommendations for safe use and disposal of the material. The target audience for information in a MSDS is the occupation worker who may be exposed to chemicals at work. However, much of the information is also relevant to consumers.
Read the manufacturers application instructions and then obtain and read the MSDS sheet to ascertain the chemicals used. Although it should be said that an MSDS is a document that contains details of the hazards associated with a particular chemical and provides information regarding its safe use. The MSDS is required to state the chemical's risks, safety and impact on the environment.
An MSDS is a fact sheet developed by manufacturers describing the chemical properties of a product. Material Safety Data Sheets include brand-specific information such as physical data (solid, liquid, colour, melting point, flash point, etc.), health effects, first aid, reactivity, storage, handling, disposal, personal protection and spill/leak procedures.
How to Read a Material Safety Data Sheet (MSDS) http://www.cmhc-schl.gc.ca/en/co/maho/gemare/gemare_012.cfm
Chemical Information (MSDS) A-Z- http://www.ehso.com/msds.php
Definitions of Terms Used in Material Safety Data Sheets (MSDS) - http://www.ehso.com/msdsdefs.php
Chemical Abstracts Service (CAS)
Each CAS registry number (often referred to as CAS #) is a unique numeric identifier that designates only one substance; it has no specific chemical significance, but is a link to a wealth of information about a specific chemical substance. Since CAS Registry Numbers are not dependent upon any system of chemical nomenclature, they can provide a reliable common link between the various nomenclatures terms used to describe substances. And serve as an international resource for chemical substance identifiers used by scientists, industry, and regulatory bodies
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.
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