pH - The Power of Hydrogen
by Roger McFadden
ACIDS, BASES AND SALTS
Acids, bases and salts are among the most important chemical compounds used by chemists. A variety of maintenance chemicals contain these compounds. For instance, hydrochloric, phosphoric and citric are acids used to make mineral stain removers, toilet bowl cleaners, metal cleaners and rust removers. Alkali maintenance chemicals like degreasers, oven cleaners and drain openers contain bases such as sodium hydroxide, potassium hydroxide, sodium metasilicate, trisodium phosphate and ammonium hydroxide. Special salts like sodium lauryl sulfate, sodium EDTA and ammonium ethoxysulfate are formulated into carpet shampoos, hand soaps and carwash detergents to provide more efficient cleaning.
Acids, bases and salts contain ions of the element hydrogen. Ions are atoms or molecules that have lost or gained electrons. If atoms lose one or more electrons they become positively charged ions (cations). If they gain one or more electrons, they become negatively charged ions (anions). It is the presence of the hydrogen ions in solutions that allows us to measure the pH of a solution. The quantity of hydrogen or hydroxyl ions in a solution determines whether the solution is acid or alkaline.
SIMPLIFYING A FORMULA
In 1909, Danish biochemist, S.P.L Sorensen proposed the use of a logarithmic scale to express the concentration of hydrogen ions (H+) and hydroxide ions (OH -). This scale has become known as the pH scale. Sorensen knew that water had a nearly balanced concentration of positive (H+) and negative (OH-) ions. The positively charged ions are called hydrogen ions and the negatively charged ions are called hydroxide ions. Scientists measured the concentrations of hydrogen ions in pure water, acidic water and alkaline water. The pure water contained a hydrogen ion concentration of 1 x 10-7 moles. The acidic water (hydrochloric acid) contained a hydrogen ion concentration of 1 x 100 moles. The alkaline water (sodium hydroxide) contained a hydrogen ion concentration of 1 x 1014 moles.
The hydrogen ion concentration was found to vary over fourteen powers of 10. A change of one pH unit changes the hydrogen ion concentration by a factor of ten. For example, a solution with a pH of 1 has 10 times more hydrogen ion concentration than a pH of 2; One hundred times more hydrogen ion concentration than a pH of 3 and so forth. This means that a solution with a pH of 1 has one million times more hydrogen ion concentration than a pH of 7. To avoid dealing with these incredibly complex exponential, scientists proposed a simplification. They converted the exponents -7, 0 and -14 to 7, 0 and 14 respectively. Subsequently, the pH scale was established ranging from 0 to 14 with the mid-point of 7 indicating neutrality. Therefore, the scale of ordinary pH values extends from 0 to 14. The pH of a neutral solution is 7. Thus the range of acid pH values extends from 0 to 7, and that of alkaline values from 7 to 14.
A GOOD WARNING SIGN
It is difficult to give an exact definition of pH. A couple of simple descriptions offered are, "power of Hydrogen" and "potential Hydrogen" ion concentration. Neither are perfect descriptions. Both present a way of remembering the significance of "p" and "H". Simply stated, pH tells us whether a solution is acid, alkaline or neutral. It does not tell us how much acid or alkali is present. It is a good "warning sign" (Proceed with Caution), but it does not establish whether the compound is corrosive or dangerous.
pH is a critical measurement. Life depends upon it. For instance, human blood is basic with a pH between 7.3 and 7.5. If the pH of blood drops below 7.3, acidosis occurs. If the blood pH rises above 7.5, alkalosis occurs. Death will occur if blood pH goes below 7.0 or above 7.8. Our human existence depends upon a balanced and buffered blood pH.
The pH of a cleaning product does not signify cleaning performance or strength. It simply indicates the concentration of hydrogen or hydroxide ions. For instance, the performance of a cleaning product cannot be determined simply by knowing the pH of the product. A common misconception about cleaning products suggests that a higher pH means superior cleaning.
SEVERAL METHODS FOR MEASURING pH
There are several methods used to measure pH. Two of the simplest are litmus paper and liquid acid-base indicators. The most widely used method is the pH meter. These meters are easy to use and very accurate. When chemists want to measure the amount of alkali or acid in a solution, they use a process called, titration. Titration measures the amount of alkali and/or acid in a solution. pH measures the concentration of hydrogen ions present in a solution. Both are important.
Most pH values are measured either by electrometric determination (pH meter) or by colorimetric methods with the aid of indicator solutions or indicator papers. The pH meter determines a precise pH with the aid of a suitable electrode submerged in the unknown solution. A direct and immediate reading is registered on the pH meter scale. The pH of a solution may also be determined by adding a few drops of indicator solution to the unknown solution. The resultant color of the mixture is then compared with a reference scale. Special high class filter papers impregnated with suitable indicator solutions can be submerged into the unknown solution and the resultant color of the paper is compared with a reference scale. The indicator papers are a simple method of determining a broad assay of acidity or alkalinity. They are not as precise as the other methods.
IMPORTANCE OF pH IN OUR LIVES
Professionals know the importance of understanding pH. For example, floor care experts use neutral pH (7) floor cleaners for daily maintenance and alkaline pH (12-13) for finish removal. Professional carpet cleaners select carpet cleaning agents with pH's between 7 and 10 to avoid potential carpet damage. Agricultural specialists control soil pH to enhance plant growth. Pool care personnel keep swimming pools and hot tubs pH balanced for safety and protection. Laundry experts keep the pH above 9.5 during the bleach cycle to protect fabrics from bleach attack. Industrial plants control the release of sulfur dioxide to control harmful acid rain from damaging our environment. These are a few of the thousands of ways pH plays an important role in our lives.
NEVER IGNORE pH VALUES
It is important for every cleaning professional to have a basic understanding of pH. Ignoring the pH of a solution can be expensive. Floor coverings and surfaces can be damaged by an inappropriate pH value. Be careful and select cleaning products with compatible pH values to match your surface requirements.