Final Assessment: Acids and Bases and the pH scale
In order to construct acid-base indicators using organic substances, it is first
necessary to understand terms and concepts related to the pH scale. According to Svante
Arrhenius acids are compounds which, when dissolved in water produce hydrogen ions
(H+), bases are compounds which, when dissolved in water produce hydroxide ions (OH). The strength of an acid or a base is the relative number of hydroxide and hydrogen ions
measured by the pH scale. Thus, the pH is “the negative of the common logarithm of the
hydronium ion concentration of a solution” [(6), p.485].
Acids described by Arrhenius are ionizable hydrogen atoms which when
combined with water form a hydronium ion (H3O+). In aqueous solutions all hydrogen
ions are hydronium ions. However, water molecules can also lose a hydrogen forming
hydroxide ions (OH-).
Svante Arrhenius was a 19th century scientist who explored the connection
between electricity and chemical force binding atoms together. Arrhenius discovered that
when electrolytes, substances that dissolve in water to create a solution which conducts
electric current, are dissolved in water they split into ions which are positive and
negative. He found that the nature of the substance and the degree of its dilution in water
influenced the degree to which the split occurred. Arrhenius continued his investigation
and “was able to prove the influence of the electrolytic dissociation on the osmotic
pressure, the lowering of the freezing point, and increase of the boiling point of solutions
containing electrolytes” (9). Arrhenius applied this knowledge to the investigation of
toxins, anti-toxins, digestion, absorption, and gastric and pancreatic juices.
The body is made up of approximately 80% water, the biological purpose of
which is to allow nutrients, bio-chemicals, and oxygen, to be transported. The properties
of “these water based mediums can (be) either acid or alkaline” (2). The acid or base is
measured by the potential hydrogen scale (pH). The pH scale reads as follows, “1.0 – 6.9
is considered acidic. 7.0 is neutral. 7.1 - 14.0 is alkaline” (4). When the pH number is low
the amount of acidity in the body is great, and when it is high the alkalinity is great. With
every decrease in pH by one unit, there is ten-fold as much of an increase in hydrogen ion
concentration.
The properties of acids and bases are important in the human body. The stomach
contains hydrochloric acid and peptidase which break down food so that it can be
digested. Too much acid in the stomach can cause irritation and ulcers. An overly acidic
stomach is soothed by an antacid. An antacid is basic and bases neutralize stomach acid
to bring the stomach back to a pH level of 2. The chemical reaction for what happens in
the body is: 2 HCl(aq) + CaCO3(s) Æ CaCl2(aq) + H2O(l) + CO2(g). (5). Some common
antacids are Mylanta, Pepcid, and Zantac. I suffer from gastritis, and therefore I know
first hand what it feels like when there is an abundance of acid in my stomach. The lining
of the stomach becomes inflamed, causing great pain. I take Zantac to control the amount
of acid in my stomach, and I have found it to be helpful in dealing with my condition.
The strength of an acid can be determined using universal litmus paper. The
procedure for testing acidity or basicity begins by dipping the litmus paper into the
substance. Then, the pH of the substance can be found by comparing the color on the
litmus according to the range of colors on the pH scale. The pH scale is numbered from
0-14, with zero being the most acidic, and 14 being the most basic. The transition interval
is the range of colors over which the indicator changes. On the pH scale red-orangeyellow colors indicate greater acidity, green indicates neutrality, and blue-purple colors
indicate basicity. For example, methyl orange has a pH ranging from 3.1 – 4.4 which
indicates that it is a strong acid. Apple juice measures 3 – dark yellow on the pH scale.
This indicates that apple juice is acidic.
It is important for our health that we maintain a stable pH which is neither too
acidic, nor too basic. Buffers are solutions which chemically neutralize acids and bases
without causing a drastic change in the pH. They are made up of a weak acid and a salt,
or a weak base and a salt. There are many natural buffers in our environment. These
include: milk and yogurt which coat the lining of the stomach. Aspirin is acidic and can
cause irritation to your stomach. Aspirin can come buffered with an antacid in order to
protect your body from the effects of over-acidity. Human blood contains buffers which
consist of carbonic acid and ions of hydrogen carbonate. The main threat of your pH from
blood is the chemical reaction that results from the production of hydrogen ions. The
blood buffer removes the hydrogen ions thus maintaining the pH between 6.8 and 7.8.
The chemical reaction for this is: HCO3-(aq) + H+(aq) Æ H2CO3(aq). [(10) p. 585]
The pH level has many important effects on health, disease, and body chemistry.
Imbalances within pH cause problems within the body. Therefore the body does
everything it can in order to maintain a balanced pH level. All systems of the body,
including breathing, circulation, digestion, and hormonal production, help to balance the
pH as well as remove toxins and acid residues from the systems (2). Intracellular pH is
important in maintaining good health. When intracellular pH shifts, becoming more
acidic, a pH cascade begins. This makes the body more susceptible to reproducing, “bad
bugs” which “give off acidic toxins, which further increases the acidity of the bio-terrain
enhancing it into an even more fertile environment” (3). Exposure to second hand smoke,
digestion of a meal high in saturated fats and extreme stress can affect the bio-terrain
significantly. In the blood stream, “when the pH levels of blood or other key bodily fluids
fall out of optimal pH range due to adverse metabolic or respiratory conditions, the
human body goes through a variety of adjustments to try to correct the acid or alkaline
imbalance” (7). This is also relevant when looking at body temperature. The normal body
temperature for a human is 98.6 degrees Fahrenheit. When this temperature increases or
decreases it causes serious changes to our body systems. Therefore, it is extremely
necessary to keep this temperature constant, and remain in homeostasis. In essence the
body’s metabolic process functions best with a balanced pH.
Acids and bases and pH play an important role in the chemistry of the body. A
shift of the pH can cause major consequences for good health. To maintain good health it
is necessary to understand the function of acids and bases in the body.
Experiment -To Find the pH level of a substance
Objective: To find the pH level of household objects.
Materials: red cabbage, measuring cup, paper towels, plastic cups, baking soda, vinegar,
shampoo, lemon juice, organic milk, mildew remover, hand soap, Pepsi, Tums, orange
juice, baking powder, Seltzer, Sprite, pH color chart.
Procedure:
1. Boil a red cabbage for 10 minutes
3. Strain the cabbage from its juice, to make the pH indicator.
4. Collect measuring cup, and plastics cups.
5. Fill a cup with 50 mL of one substance.
6. Pour the cabbage juice indicator into a cup with a substance in it.
7. Determine the pH level of the substance by using the pH color chart.
8. Record results.
9. Repeat steps 5-8 for the other substances.
Data:
Substance
pH
Color
Baking Soda
Vinegar
Shampoo
Lemon Juice
Milk (organic)
Tilex Mildew Remover
Hand Soap
Soda
Tums
Orange Juice
Baking Powder
Seltzer Water
Sprite
8
2
8
2
8
14
6
2
7
3
8
2
1
Blue
Red
Purple/red
Red
Blue
Yellow
Pink/Purple
Dark Red
Purple
Orange/Red
Blue/Purple
Pink/Purple
Pink
Bibliography
(1) “Acids – Suceed in Physical Science.” 7 Jun 2005. <http://www.school-forchampions.com/science/chemacids.htm>
(2) ”Balancing Internal pH for Better Health” 5 Jun 2005. <http://spiritualendeavors.org/health/Internal%20pH.htm>
(3) “Biological Terrain Assessment” 12 Jun 2005. <http://www.totalcare.org/ba.htm>
(4) “Body pH Levels” 5 Jun 2005. <http://www.souzaoenterprises.com/pH.html>
(5) “Chemistry 104: Analysis of an Antacids Tablet” 7 Jun 2005.
<http://www.chem.latech.edu/~deddy/chem104/L3Antacid.htm>
(6) Davis, Raymond E., John E. Williams. Modern Chemistry. Holt, Rinehart, and
Winston: 2002.
(7) “pH Balance in the Human Body” 11 Jun 2005. <http://www.ccone.com/nh1/phbalance.html>
(8) “pH Scale” The pH Scale. 4 Jun 2005.
<http:staff.jccc.net/pdecell/chemistry/phscale.html>
(9) “Svante Arrhenius –Biography” 5 Jun 2005.
<http://nobelprize.org/chemistry/laureates/1903/arrhenius-bio.html>
(10) Wilbraham, Antony C., Dennis D. Staley, Michael S. Matta. Chemistry. AddisionWesley: 1995.