EFFECT OF ACID RAIN ON MARBLE STATUES

Knight Foundation Summer Institute

Terry Newirth, Haverford College

Introduction:

This is an example of an acid/base reaction, one of the two most common forms of chemical reactions. In an acid/base reaction an acid gets neutralized by a base to form water and a salt. The acids are usually easy to identify as they have a low pH in water, and their chemical formula always has at least one "H". Bases are harder to identify without knowing a lot more chemistry. The most common base is hydroxide ion -OH which is found in drain cleaning products like "Drano" or "Red Devil." In this reaction the base is the carbonate ion, CO3-2. It reacts with H+ of acetic acid to form carbonic acid, H2CO3, which mostly turns into carbon dioxide and water.

In this experiment our purpose is to demonstrate the effect of acid rain on limestone, a major constituent of marble.

Objectives:

  1. To introduce the students to the concept of an acid-base reaction
  2. To demonstrate when these reactions take place in the lives of the students
  3. To show the students the effects of acid rain

Vocabulary:

Limestone

Neutralized

Materials:

Procedure:

  1. Create in your lab book a table similar to the one shown below
  2. With a marking pen, label the beakers 1, 2, 3, and 4
  3. Measuring with a graduate cylinder, place 10 ml of water in beakers #1 and #2, and 10 ml of vinegar in beakers #3 and #4
  4. Tear off two small pieces of pH paper (about 1 cm long) and using the tweezers to hold them dip one piece into beaker #1 and piece into beaker #3. Compare the color of the pH paper to the pH color chart and record the pH in the Table you created in your lab book. The pH of beaker #2 should be the same as #1 and the pH of beaker #4 should be the same as #3.
  5. Take four marble chips of comparable size. Rinse them off in water and dry them with a paper towel
  6. Weigh and record the weight of two marble chips which should then be placed in beaker #2
  7. Weigh and record the weight of the other two marble chips which should then be placed in beaker
  8. Record any observations in your lab book
  9. The next day tear off four small pieces of pH paper and measure and record the pH of the liquid in all four beakers
  10. Using the tweezers, remove the marble chips from beaker #2. Rinse the chips off in water, dry them and then weigh and record the mass in your data Table
  11. Using the tweezers, remove the marble chips from beaker #4. Rinse the chips off in water, dry them and then weigh and record the mass in your data Table

Suggested Table for Recording Data:

This should be in your lab book.

Beaker

Liquid

pH original liquid

G marble chips orig.

pH next day

G marble chip next day

1

Water

 

None

 

None

2

Water

 

 

 

 

3

Vinegar

 

none

 

None

4

vinegar

 

 

 

 

 

Observations / Conclusions:

There should be no observable change in the marble chips in water. There are no bubbles, the pH does not change and the mass of the chips does not really change either.

When the marble chips are placed in vinegar, one immediately sees bubbles forming. After a day, one can also observe that the pH of the vinegar with the chips has been raised to pH = 6, while the pH of the vinegar control has not changed at all. The mass of the limestone chips is also decreased by the apparent reaction. The bubbles which one sees are CO2 formed from the acid base reaction of vinegar and limestone:

Vinegar limestone

2HOAc + CaCO3 CO2 + Ca(OAc)2 + H20

The calcium acetate that is formed is soluble in the water so you can't see it.

Note this reaction is similar to the acid/base reaction we used to generate CO' from vinegar and baking soda.

Assessments:

-The students should turn in their data tables as well as their interpretation of their results. Some questions to help your students with their write up are:

-Have a class discussion about the other effects of acid rain on our environment. You may ask the students to come prepared by looking in the library or on the internet for some ideas and information.

-Let the students each write a creative story on the effects of acid rain on the environment, e.g. from the point of view of the statute, or of a fish in a pond polluted with acid rain.

Extensions:

"A Green Penny?" and Must it Rust?" are two other labs that deal with the effects of acid rain. For experiments on chemical reactions on general see also "Lose the Indicator Blues."

Philadelphia Science Content Standards:

HUMAN SOCIETY: THE COMPLEX EPE~CTS OF SCIENTIFIC ACTIVITY ON SOCIETY AND OF SOCIETY ON SCIENCE

This is an example of an industrialized world on nature and the structures that we build.

SCIENCE CONTENT STANDARD # 1: NATURE OF SCIENCE

This content allows the students to "design, modify and conduct an investigation through testing, revising, and occasionally discarding idea, all of which lead to a better understanding of how things work." Also, as benchmark number 2 states, the students will learn to "collect and summarize data from an experiment and interpret results in terms of the data."

SCIENCE CONTENT STANDARD #2: PHYSICAL SETTING

Benchmark 5 in the (k-4) section of this standard is covered by this experiment. The standard requests that the students "observe how materials change over time (e.g. metal rusting)."

Cross References:

The students will learn more about chemical reactions, the importance of water as well as the environment from this experiment. In the extensions, the students will be using Language Arts skills to find out information from the library and the internet as well as writing the creative story on acid rain.