When cleaners get together and discuss technical topics the subject of pH is
likely to come up. Even more so has this been true of dialogue that include
industry instructors, product formulators and chemists. What is behind the flap?
Realizing that IICRC carpet cleaning classes are not college chemistry classes,
instructors and others on the committees working on the content of the classes
wanted to keep things simple. Efforts to simply meant that some information was
left out. Many instructors had extensive personal experience in carpet cleaning
but limited training in chemistry. The statement that wool should be cleaned
using products with a pH between 4.5 and 8.0 appears to have been incorrectly
attributed to Wools of New Zealand. These factors and others resulted in
students getting a somewhat distorted view of pH as it related to cleaning.
Why You Should Understand pH
Reading an article in Cleanfax, chatting with other cleaners at Cleanfax.com
will not qualify you to formulate your own cleaning chemicals. Developing well
formulated cleaning agents including spot and stain removers is accomplished by
trained experts. They are able to test their creations in laboratories to see
how well they perform. So, please don't view this as guidance on how to mix your
own chemicals at home.
It is important to understand how and why one cleaning agent works differently
than another. This will allow you to select the best product for any particular
situation. Understanding pH will help you in your spotting efforts. Your
knowledge will demonstrate your professionalism and aid in gaining your
Most cleaning is accomplished by physical changes not chemical reactions.
Chemical reactions can remove color and damage fibers. Knowing how chemicals
will react will help us avoid damage to the carpets, rugs and upholstery we
clean. But pH is only part of the reason chemical reactions occur. Reactivity,
pH, buffering and total alkalinity all play a role.
What's the Difference between Physical Change and a Chemical reaction?
A chemical reaction means molecules of one kind are changing to molecules of
something different. For example, a chemical reaction occurs when we use an acid
rust remover. This does not physically remove the rust. Rather it changes the
rust to a new substance that is colorless. Chemical reactions also happen when
using some stain removers that add or remove oxygen from the molecules that
provide the color in a stain. This is called oxidation or reduction. More
accurately it is both oxidation and reduction at the same time. If oxygen is
added to one molecule it must have been removed from another molecule. A chemist
would call it a redox reaction.
Most cleaning involves physical changes not chemical changes. An example of a
physical change would be dissolving salt into water. This is called a solution.
Water is the solvent. Salt is the solute. Even though the salt and water are
combined, it is still water and salt. When the water evaporates, the salt will
be left behind. It did not change into something different. They remained water
and salt. Water and oil soluble soils are often removed by dissolving them and
extracting the solution.
Another type of physical combination is a mixture. A mixture occurs when two
chemicals are combined but they do not react with each other. An example would
be combining salt and sugar. There is no chemical reaction to form a new
compound. Neither is dissolved by the other. The salt and the sugar are mixed
together but remain distinct from each other.
Water and oil do not usually mix. Cleaning agents may break up oil into tiny
droplets suspended in the water. This is called an emulsion. An emulsion is one
type of a mixture. Oils and grease may be emulsified. The mixture of water and
oil is then extracted.
Some elements react more readily than others. Our atmosphere is another example
of a mixture. It is composed largely of Nitrogen along with oxygen, carbon
dioxide and small amounts of other gases.
The Nitrogen seldom reacts with whatever is around it. Oxygen reacts with many
things around us. Oxygen reacts with iron to form rust. Whenever a flame is
burning something is reacting with Oxygen. Oxygen reacts with oils resulting in
a difficult to remove discoloration. These reactions have nothing to do with pH.
The key point is that the pH of the chemicals involved is only one of the
factors that determine what, if any, chemical reaction takes place.
pH - What is It and What Do the Numbers Mean?
pH tells us how many ions or electrically charged particles are present in a
liquid. The number of ions present (pH) is another of the factors that determine
if a chemical reaction will take place. You don't need to know a lot about pH
for to use it to aid your cleaning. If you want more detail read the box below.
If you prefer to 'keep it simple' skip past.
pH is an abbreviation of a French term. The English equivalent is "power of
Hydrogen." Here is the official definition of pH. pH is the negative logarithm
(in base 10) of the number of Hydrogen ions in one liter of a solution.
It is not necessary to fully understand that official definition of pH to see
how pH effects your cleaning. However, some of you are asking yourselves. "What
does that mean?"
Ions are molecules that have either gained or lost an electron. So they are no
longer electrically balanced. They will either have a negative charge (extra
electron) or a positive charge (missing an electron).
Water molecules (H2O) are composed of two atoms of Hydrogen (H) and one atom of
Oxygen (O). A very few of these molecules will separate into an H+ ion and OH-
ion. In pure water there will be an equal number of each. There will be .0000001
H+ ions (10-7) molecules in each liter of water. The pH of pure water is 7, the
negative of the power of 10 from counting those ions.
When a substance is dissolved in water the number of Hydrogen ions may increase
or decrease. If the result is fewer H+ ions the solution is alkaline. If there
are more H+ ions the solution is an acid.
The pH scale ranges from 0 to 14. Numbers below 7 are acid. Numbers greater than
7 are alkaline. The further from 7 the stronger the acid or alkaline. Each whole
number difference represents a tenfold change.
Pure water is neutral - pH 7. However, almost anything dissolved in the water,
in any amount, will affect the pH. Freshly distilled water rapidly absorbs
carbon dioxide from the air and reaches a pH of 5.5 in a very short time. Other
materials dissolved in the water may have an even more marked effect. Depending
on its chemical characteristics, it can either raise or lower the pH value. Thus
the pH of any solution depends on the type and amount of materials dissolved in
Each number on the pH scale actually represents a 10 fold difference. Thus, pH 4
is ten times as acidic as a pH 5 solution. A pH 3 solution, in turn has ten
times the strength of the pH 4 solution - and 100 times the acidity of the pH 5
solution. This pH scale of 0 to 14 is derived from the chemical properties of
water and this pH scale cannot be used without water.
To help visualize how quickly the strength changes, think of pH 7 being the
thickness of a sheet of paper. A pH of 10 is 7", about as tall as a water glass.
Moving to an 11 is the height of an average man, about 5'10"! A pH of 14 would
be well over a mile high.
Remember, the pH numbers represent only a part of the picture. Other factors
influence if there will be a chemical reaction and how strong that reaction will
be. The pH scale does not show the reactivity or concentration of a chemical.
The pH chart does not tell us if a chemical will maintain that pH or easily
change in the presence of other chemicals.
Total alkalinity indicates how well a chemical compound will maintain its pH. To
visualize this concept think about soldiers marching in formation. Let pH
indicate how many columns of soldiers in the formation. The further from 7, the
greater the number of columns. Alkalinity indicates how deep the columns are.
If something tries to change the pH, how much strength is in reserve to maintain
the ranks? Some materials tend to stabilize a solution so that it maintains a
specific pH. A buffered solution tends to resist a change in pH when acids or
alkali are added. A cleaning solution that can maintain its pH in the presence
of soil and other chemicals is said to be buffered.
Ingredients in a cleaning product that increase the total alkalinity are called
builders. Builders may be added to buffer a product. Builders also help to
counteract the effects of hard water.
The natural pH of most carpet fibers is near neutral (7). For wool, the natural
pH will be between 5.5 and 7. For the life of the fiber and to keep from
attracting soils, we should leave the fibers as close to possible to their
natural pH when we have finished cleaning.
Now that we know what pH is, let's see how to apply this information to our
pH In Our Cleaning
Most soils are acidic, averaging between 4 and 5. Soils will be easier to remove
when they are neutral. When alkaline mixes with fats, oils and grease they form
soap. Our forefathers would mix beef or pork tallow (fat) with a lye (sodium
hydroxide or potassium hydroxide), a strong alkaline to form lye soap. So the
most effective cleaning agents are alkaline.
The American Association of Textile Chemists and Colorist recommends a pH no
greater than 10.0 for use on nylon and most synthetic fibers. Cleaning agents
with higher pH can be used on olefin.
We try to leave the fibers, after cleaning, as close to a pH of 7 as possible.
Treating the fibers with an acid rinse agent or a spray application of an acid
accomplishes this. Because Mrs. Home-owner may not like the idea of acid being
sprayed on her carpet, our industry has adopted the German term for acid, soure,
to describe these products.
The pH factor can also be important in removing stains. pH can be checked with
paper strips (Phydrion paper) or an electronic meter.
To use pH paper, moisten the stain slightly with water and press a piece of
Phydrion paper to the carpet and check the color of the paper on the pH chart
provided. Some of the color may transfer to the fibers. A safer way is to scoop
up some of the moisture from the stain and apply this to the pH strip. Soils and
oil from the fingers can affect the reading, so don't touch the part of the
paper where the reading will be made. Compare the color of the paper to the
color guide on the Phydrion container to determine the pH solution of the spot.
There are some great meters available to check pH. The cost is under $100. To
check the pH with a meter - Wet the stain. Then touch the tip of the meter onto
the stain and press the button to take a reading. The pH will be shown on the
Meters can be calibrated to give answers accurate to two decimal places. Usually
this degree of accuracy is not required. Generally a cleaner does not need to
know the exact pH, only a general range. For example 0-3 would be a strong acid.
3-6 is mildly acidic. This is the range for many food spills. 6-8 is neutral on
so forth. The chart on page X will help you interpret pH readings as they apply
to cleaning and spot removal.