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Lab: Acids and Bases

Understand the properties and reactions of acids and bases

Relate these properties to common household products
Chances are you’ve seen the commercials
talking about acid-reflux disorder. Acid-reflux
is a condition that occurs when the pH of
stomach acid has decreased and is
damaging the lining of the stomach or
esophagus. Many people rely on over-thecounter tablets or liquids to relieve the
symptoms of acid-reflux and nausea. You
may be more familiar with a simple nausea
remedy – warm lemon-lime soda pop. Why
do these substances work to relieve nausea
and acid-reflux? These substances have
higher pH levels than your stomach acid.
Antacids are either a base or a basic salt and
help to raise the pH of your stomach acid by
neutralizing the excess acid. The same is
true of soda pop, an acid with higher pH than
your stomach acid.
Figure 1: Antacid tablets and liquids are overthe-counter medications that people use to
reduce the effect of a decrease in the pH level
of stomach acids.
Compounds, like acids and bases, are very important in nature and in chemistry.
Chemist Svante Arrhenius defined acids and bases this way: acids dissociate in
aqueous solutions to form hydrogen ions (H+), while bases form hydroxide ions (OH-).
Johannes Brønsted and Martin Lowry concluded that acids donate hydrogen ions (H+)
to bases (OH-), which in turn, receive the hydrogen ion (H+).
Acids and bases are physically different in many ways. Acids and bases, which you can
ingest, do not taste the same. An acid, like orange juice, tastes sour, and a base, like
soap, tastes bitter. Bases, which are normally found as cleaning products in the house,
also feel slippery. You should always exercise safety when working with any acid or
© KC Distance Learning
base. Both acids and bases can burn or dissolve human tissue. This works in your favor
in many different ways. Have you ever swallowed one of your teeth? Your stomach acid
has low pH and is capable of dissolving many different materials, including teeth and
bones. So what is pH and how does it relate to acids and bases?
As measured on the pH scale, pH refers
to a standard set of acid and base
solutions in concentrations that have
been agreed upon by an international
group of scientists. On this scale, pure
water is neutral at 7.0, solutions with a
pH of less than 7.0 are considered
acidic, and those with a pH of greater
than 7.0 are considered basic. Don’t
confuse the pH scale with p[H3O+].
In chemistry, p[H3O+] is the measure of
the molar concentration of the number of
dissolved hydronium ions (H3O+) in a
Figure 2: Sample pH scale showing the pH level of logarithmic, so 0.1 molar of hydrochloric
various acid and base solutions. Drinking water, acid has an approximate pH of 1.0, while
which can be affected by minerals and other
dissolved solids, has a pH ranging from 6.5 to 7.5 on 0.001 molar of HCl as a 3.0 pH. There
the scale. Drinking solutions, such as seawater, milk are many ways to measure pH, including
of magnesia, or other bases causes your body to
using pH indicator strips, electronic pH
dehydrate and can be dangerous to your health.
meters, and even a simple red cabbage
juice test for measuring pH. Use the following web site to create the red cabbage juice
pH indicator:
Always remember that acids and bases are some of the most reactive and dangerous
chemicals you may encounter. Individuals with bulimia or anorexia nervosa, conditions
which include constant vomiting, can burn their esophagus and mouth as well as
dissolve their teeth. Every day many individuals are rushed to emergency rooms with
burns from exposure to battery acids, while small children can easily be burned by
drinking basic solutions, such as drain cleaners. One of the most important safety
practices in chemistry is the protocol used when mixing acids or bases with water. Any
© KC Distance Learning
time you are mixing an acid or a base with water, always pour the more concentrated
solution (acid or base) into a larger volume of water.
Pre-lab Questions
1. What type of acid is stomach acid most similar to on the pH scale?
2. What would happen when you mix hydrochloric acid (HCl) with sodium hydroxide
3. Estimate the pH of the resulting solution if you mixed equal amounts of
hydrochloric acid (HCl) and sodium hydroxide (NaOH).
© KC Distance Learning
Experiment: pH Scale
In this experiment, you will be working with a simulated lab. Study the screen shot of the
simulator and pay close attention to the highlighted controls. These controls, along with
others specified in the lab procedures will assist you in successfully completing this
experiment. As you conduct each portion of the experiment, be sure to write down your
NOTE: If your experiment gets out of control, you can start over by clicking the reset
button located on the right control panel.
Materials: PhET lab – pH Scale
© KC Distance Learning
1. Start the lab with a beaker containing 1.00 liters of milk with a pH of 6.50 on the
pH scale.
2. Observe the concentrations of the hydronium ions (H3O+), hydroxide ions (OH-),
and water (H2O) in the “Water Components” chart on the right of the screen.
3. Switch the chart from a “Logarithmic” scale to a “Linear” scale using the radio
buttons located below the chart.
Observation: How did the chart change?
4. Using the “Zoom In (÷10)” button on the chart, zoom in eight times. As you zoom
in, observe how the scale on the left-hand side of the chart changes.
Observation: What is the relationship of the number of hydronium ions (H3O+),
hydroxide ions (OH-), and water (H2O) in milk?
5. Use the reset button at the bottom of the screen to reset all the settings.
6. Use the drop-down menu in the upper-left corner of the screen to add 1.00 liters
of battery acid to your beaker.
7. Use the drain bibcock to drain the battery acid to a level 0.10 liters in the beaker.
NOTE: This is a difficult procedure and a level of approximately 0.10 liters is
Observation: What is the relationship of the number of hydronium ions (H3O+),
hydroxide ions (OH-), and water (H2O) in the battery acid? What is the pH of the
battery acid as indicated on the pH scale in the center of the screen?
© KC Distance Learning
8. Observe the number concentration on the “Water Components” chart.
9. Use the water bibcock to add 0.10 liters of water to the solution to create a 0.20liter solution of battery acid.
Observation: How did the pH level and the water components level change after
adding water to the battery acid?
10. Use the water bibcock to add 0.30 liters of water to the solution to create a 0.50liter solution of battery acid.
Observation: How did the pH level and the water components level change after
adding water to the battery acid?
11. Use the water bibcock to add 0.50 liters of water to the solution to create a 1.00liter solution of battery acid.
Observation: How did the pH level and the water components level change after
adding water to the battery acid?
© KC Distance Learning
12. Repeat steps 5 through 11 for another liquid. Be sure to write down all of your
Post-lab Questions
1. How much water is required to dilute an acid or a base? Explain your answer.
2. Compare the results from the observations you made with the battery acid to those
of the acid or base you observed in step 12 of the experiment.

3. List two acids and two bases you come in contact with on a regular basis. Which of
these is has a pH farthest away from pure distilled water?
© KC Distance Learning

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