Both "acid" (MAA/MAP) and "non-acid" primers are "acidic" (a pH lower than 7). Some are just more acidic than others. The term "non-acid" is a standard misnomer used to identify those primers that are less acidic and/or do not use methacrylic acid (MAA/MAP) as their main ingredient. (Remember, this is relative since we as human beings are acidic! So, "acid" is NOT bad.)
Being acidic is not BAD. Being either side of a pH of 7 (neutral, which is water) is equally "different". Being "different" than water one-way or the other is not BAD, it's just DIFFERENT--- and for a reason and for a purpose. Something with a pH of 10, say acetone for instance (so 3 more than 7) is the "same" as far as that pH factor goes as something with a pH of 4 (so 3 less than 7) in comparison to water.
What is pH?
pH is the Unit of Measure used to express the degree of acidity of a substance. The centimeter is a unit measure of length. The gram is a unit measure of weight. Therefore, pH is the unit measure we use to say how much acid is in a substance. The pH scale goes from 0 to 14. A pH of zero means a very high acid activity. Substances such as lemon juice and vinegar are acidic with pH values of 2 to 3. Nitric acid and hydrochloric acid are very strong with pH values of 0, while stomach acid has a pH of 1. Addition of a strong acid, such as sulfuric acid (H2SO4) to water makes the resulting solution very high in active acid concentration. This is called an acidic solution.
On the other end of the scale are the alkaline substances, which range from 8 to 14. Common alkalis are seawater (pH 8), household ammonia (pH 11), oven cleaners (pH 13), and the very strong alkali, sodium hydroxide (pH 14). The addition of a strong base or alkali material, such as sodium hydroxide ( NaOH), to water makes the resulting solution very low in active acid concentration. This is called a very basic or alkali solution.
In between these two extremes is a pH of 7. This is the pH of pure water. Water, which is neither very acidic nor very alkali, is said to be neutral. pH stands for (in our simplified technical purposes) HYDROGEN! As in HOW much hydrogen in the chemical in question as in relation to the amount of hydrogen in WATER (good old H2O as in 2 parts hydrogen to one part oxygen.
Technically, the scale actually refers to the concentration of positively-charged hydrogen (H+) ions and negatively-charged hydroxyl (OH-) ions in solution. More hydrogen ions than hydroxyl ions make an acidic solution, while an alkaline solution contains more hydroxyl ions than hydrogen ions. The pH scale is a logarithmic one, meaning that each pH unit has 10 times as many hydrogen ions as the unit above it. Therefore, at pH 4, there are 10 times more hydrogen ions than at pH 5 and 100 times more hydrogen ions than at pH 6.
pH, range of numbers expressing the relative acidity or alkalinity of a solution. In general, pH values range from 0 to 14. The pH of a neutral solution, i.e., one that is neither acidic nor alkaline, is 7. Acidic solutions have pH values below 7; alkaline, or basic, solutions have pH values above 7. A pH value provides a measure of the hydrogen ion concentration of a solution. In pure water, the concentration of hydrogen ions is equal to 0.0000001, or 10-7, moles per liter. (A mole is the amount of a substance, expressed in grams, that is equal to the molecular weight, or formula weight, of the substance.) When an acid is added to pure water, the hydrogen ion concentration increases above this level. When an alkaline substance, or base, is added to pure water, the hydrogen ion concentration decreases below this level. Once the concentration is determined, the pH value is found by taking the exponent used in expressing this concentration and reversing its sign. This is expressed as pH=-log10 [H+]. For example, if the hydrogen ion concentration of a solution is 10-4, or 0.0001, moles per liter, the pH is 4.
"Hydrogen ions determine pH. The quantity of hydrogen ions at or near a sensor surface cause an electrical effect that can be detected and measured by the appropriate instrumentation, thus pH is then derived.” Higher pH levels are called BASE substances (over 7); lower pH levels are called ACID substances (under 7).
Sample pH Measures
The pH of our nails is appox 5.5. This is a conglomeration of the pH of other things going on in our bodies, a huge component of which of course is WATER. Which while is normally construed to be 7.0, can actually be found to be "normal" at anywhere from 5.5 to 8.0 (and more or less). Our blood has a neutral pH of 7.2.
Other common pH's: Stomach acid 1.0, Lemon Juice 2.4, Common House-Hold Vinegar 2.4 to 2.8 (for concentrations of 6% to 3% accordingly), Orange Juice 3.0, Tomato Juice 4.0, Black Coffee 5.0, Clothes Detergent 6.5,Milk 6.8, Blood 7.2, Seawater 8.0 (notice how addition of salt reduces the acidity and raises alkalinity), Baking soda 9.0, Bath Soap 9.5, Acetone and/or Isopropyl Alcohol appox/estimated at 10.0 (depends on concentration of water added, which varies), Milk of Magnesia 10.7 (designed to reduce stomach acids :), Laundry Bleach 11.0, Caustic Soda 14.0
Methacrylic acid primer pH varies widely based on the content of MAA and other solvents (and given that pH is a logarithmic calculation we can see how 1/10 a point here or there is a huge difference), but generally would fall somewhere between that of stomach acid (ph 1.0) and vinegar (AKA acetic acid @ 3% for a pH 2.8), around 2.0 as an average pH for acid primers.