Acid Rain and pH Lab

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					Acid Rain pH Lab                                                               -1-


ACID RAIN PRIMER - What does pH mean?

The initials pH stand for “Potential of Hydrogen.” This is a measure of how
acidic or alkaline a substance is relative to the pH of water. The pH of water is 7
substance has the more acidic it is. and considered neutral because it contains
equal amounts of H + and OH – ions. When an acid is poured into water, it loses
a H + (hydrogen ion) to the water. The water has become more acidic because
it has gained an H + The more H + a Acids have pH values < 7.

When a base is poured into water, it gives up a OH - (hydroxide) to the water.
The water has become more basic because it has gained a OH - . The more OH         -

a substance has the more basic or alkaline it is. Alkalis have pH values over 7.

Please see the pH scale below:

                                 pH




Because the pH scale is logarithmic, a difference of one pH unit represents a
tenfold, or ten times change. For example, the acidity of a sample with a pH of 5
is ten times greater than that of a sample with a pH of 6. A difference of 2 units,
from 6 to 4, would mean that the acidity is one hundred times greater, and so
on.
Acid Rain pH Lab                                                               -2-


Environmental Science – 1-Day pH Lab with Homework

Name:______________________

Objective: We want to illustrate how pH changes occur by adding H + or OH –
ions to common substances and to understand the reactions in the atmosphere
that form acid rain.

Students will work with a partner. Each team needs the following
materials:

tap water                  3 glass beakers (100 ml size)
Ammonia                    safety goggles
penny                      pH paper with color coded chart
distilled water            3 plastic medicine droppers
lemon juice                5% acetic acid (vinegar)
nitric acid                sulfuric or sulfurous acid
carbonic acid              limestone (Ca OH2) and ¼ tsp.
dropper bottles

Directions:

Task 1. Put on your safety goggles.

Task 2. Using the pH paper, determine what the pH is for the following
substances: distilled water, lemon juice, nitric acid, sulfurous acid, ammonia, and
vinegar. To accomplish this task, use a medicine dropper to withdraw your
sample of liquid from the beaker and then place a drop of the liquid on the pH
paper. Use the color- coded scale that is provided to determine what the pH of
the liquid is. Record your findings on the chart provided below.

pH            Substance                         More H + or More OH – ion?

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Acid Rain pH Lab                                                               -3-




Task 3. Mix equal amounts of distilled water and lemon juice together. Add 10
ml of lemon juice to 10 ml of water. Swirl gently. Test the pH of this mixture.
Record your observation in the chart above. Did the pH of the water change
when you added lemon juice to it? Did it become more acidic or more basic?
Write your thoughts down in the space provided below:
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Read the following description of how acid rain forms:

Normal rain has a pH of about 5.6. It is slightly acidic because of the formation
of carbonic acid that occurs naturally.

Carbonic acid occurs when carbon dioxide gas dissolves in rain droplets of
unpolluted water. Remember plants release CO2 during cellular respiration.

CO2   (g)   + H2O   (l)    H2CO   (aq)


Rain measuring between 0 and 5 on the pH scale is referred to as acid
rain. How is acid rain formed in the atmosphere? There are two
reactions in the atmosphere that produce acid rain.

1. Nitrous acid and nitric acid result from a common air pollutant, nitrogen
dioxide (NO2). Most nitrogen dioxide in our atmosphere comes from automobile
exhaust. Nitrogen dioxide gas dissolves in rain drops and forms nitrous and
nitric acid.

2NO2    (g)   + H2O   (l)    HNO2 (aq) + HNO3 (aq)

2. Sulfurous acid is produced from another air pollutant, sulfur dioxide (SO)2.
Most sulfur dioxide gas in the atmosphere comes from the burning of coal which
contains sulfur impurities. Sulfur dioxide dissolves in rain drops and forms
sulfurous acid (H2SO3 ).
.
SO2 (g) + H2O (l)  H2SO3 (aq)
Acid Rain pH Lab                                                              -4-




Task 4. Add five drops of nitric or sulfurous acid to 10 ml distilled water. Swirl
gently and then test the pH. What happens to the pH of the water? If nothing
happened, add 5 more drops. Swirl gently and test the pH. How many drops of
acid did you have to add before you saw a change in the pH of the water? Write
down your observations here.
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Task 5. Add ¼ tsp. limestone to the nitric acid solution that you made in Task
4. Swirl gently. Test the pH of this new mixture. Did you see a change? If
not, add another ¼ tsp. limestone. Swirl gently to mix. How much limestone
did you have to add before you saw a pH change? Write down your
observations here.
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Task 6. What is the pH of your saliva?___________

Task 7. At home tonight add about 10 ml vinegar to a glass. Place a penny in
the glass. Let it soak overnight in the vinegar. What happened to the penny?
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Acid Rain pH Lab                                                                     -5-


Name________________________

Environmental Science

Homework Assignment – pH Lab on Acid Rain

Please answer the following questions:

   1. Is rain getting more or less acidic? Take a look at the illustrations. What is the
      pH of the rain in your area?
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Acid Rain pH Lab                                                                  -6-


2. Here are the effects of acid rain on the inhabitants of a lake that has become
acidified.

  As water pH
                                                Effects
  approaches
       6.0              crustaceans, insects, and some plankton species begin to
                         disappear.


       5.0              major changes in the makeup of the plankton community
                         occur.
                        less desirable species of mosses and plankton may begin to
                         invade.
                        the progressive loss of some fish populations is likely, with
                         the more highly valued species being generally the least
                         tolerant of acidity.


  Less than 5.0         the water is largely devoid of fish.
                        the bottom is covered with undecayed material.
                        the near shore areas may be dominated by mosses.
                        terrestrial animals, dependent on aquatic ecosystems,
                         are affected. Waterfowl, for example, depend on aquatic
                         organisms for nourishment and nutrients. As these food
                         sources are reduced or eliminated, the quality of habitat
                         declines and the reproductive success of birds is affected.




Not all lakes that are exposed to acid rain become acidified. In areas where
there is plenty of alkaline material such as limestone, lakes are better able to
neutralize the acid. In Canada where the acid rain falls, there is not much
alkaline material. Looking back at the illustration in the previous question, what
effects would you expect to see in the ecosystem of the lakes located in the red
zone?
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Acid Rain pH Lab                                                                -7-


3. There are a number of things you can do as an individual to reduce acid rain.
The burning of fossil fuels (e.g. coal, oil, gas) is the source of the gases that
form acid rain in water. By conserving electricity, you will be reducing the
demand for electricity and therefore, there will be less need to burn coal and oil.
List at least ten things you can do around the house to use less electricity.
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4. Of course, you can also make some changes in the way that you use
transportation to reduce the use and burning of fossil fuels (e.g. gasoline, oil).
What would you be willing to do differently than you do now to conserve energy?
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