Buffering of Lakes and Streams

Demonstration Kit


Acid rainfall causes deleterious effects to our environment. It can be especially harmful to the ecosystems of lakes and streams. Help students discover natural defenses that allow lakes and streams to maintain pH.


  • Acid rain
  • Acid–base indicators
  • Buffers
  • Water quality


Marble chips (calcium carbonate, CaCO3), 60 g*
Sulfuric acid, H2SO4, 0.1 M, 3–5 mL*
Universal indicator solution, 12 mL*
Water, distilled or deionized
Beaker, 250-mL
Beaker, 400-mL
Cotton ball*
Glass demonstration tube, 1.4 cm x 60 cm*
Graduated cylinder, 25-mL
Pipets, Beral-type, or eyedroppers, 3*
Rubber stopper, 1-hole to fit tube, size 00*
Stirring rod
Support stand and buret clamp
*Materials included in kit. 

Safety Precautions

Dilute sulfuric acid solution is corrosive to eyes, skin and other tissue—avoid contact of all chemicals with eyes and skin. Wear chemical splash goggles, a chemical-resistant apron and chemical-resistant gloves. Please consult current Safety Data Sheets for additional safety, handling and disposal information.


Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. The buffered filtrate and dilute acidic rainfall solution may be rinsed down the drain with an excess of water according to Flinn Suggested Disposal Method #26b.

Prelab Preparation

Part A. Preparing the “Acid Rainfall” Solution

  1. In a 400-mL beaker, combine 200 mL of deionized water and 12 mL of universal indicator.
  2. Using a Beral-type pipet, add 1–2 drops of 0.1 M sulfuric acid to the indicator solution until it turns red (pH ≤4).
Part B. Constructing the Column
  1. Place one cotton ball into one end of the long glass demonstration tube. Stopper this end of the demonstration tube with a one-hole rubber stopper.
  2. Add about 60 g of marble chips to the demonstration tube.
  3. Using a single buret clamp, attach the demonstration tube vertically to a support stand so that the stoppered end of the tube is at the bottom and the open end is at the top.
  4. Place a 250-mL beaker under the stoppered end of the tube. Rinse the column of marble chips with water until the water comes out clear, not cloudy.
  5. Empty, rinse and replace the beaker under the tube.


  1. Fill the column of marble chips halfway with distilled water. Quickly proceed to step 2.
  2. Slowly pour about 25 mL of the “acid rainfall” solution into the top of the demonstration column.
  3. Observe the rainbow spectrum of color changes as the acid rain solution slowly filters through the column. Continue pouring the rainfall solution into the tube.
  4. Record observations in the Buffering Lakes and Streams Worksheet. Note the color of the filtrate after all of the acid rain solution has passed through the column.
  5. Using a Beral-type pipet, slowly add more acid rain solution to the filtrate in the beaker. Stir the filtrate with a stirring rod or using a magnetic stirrer. Observe the indicator color of the “naturally buffered lake” created in the beaker.
  6. Use a Universal Indicator Color Chart to correlate the relationship of the buffer color and the pH of “acid rainfall” solution.

Student Worksheet PDF


Teacher Tips

  • This kit contains enough chemicals to perform the demonstration seven times: 300 g marble chips (reusable), glass demonstration tube, 35 mL 0.1 M sulfuric acid, 100 mL universal indicator.
  • Rinse used marble chips with water several times before starting a new demonstration.
  • Bromcresol green may be used as an alternative acid–base indicator for this demonstration. Bromcresol green is yellow when the pH is < 3.8, blue when the pH >5.4, and green in the intermediate or transition range between these two values. The color changes for bromcresol green occur at the lower pH limit for natural or normal rainfall.

Further Extensions

  • As an extension of this activity, fill parallel demonstration tubes with marble, granite and sand and compare the effectiveness of different “soil types” in neutralizing acid rain. Test local soil samples to determine their buffering capacity as well.

Correlation to Next Generation Science Standards (NGSS)

Science & Engineering Practices

Developing and using models
Planning and carrying out investigations
Analyzing and interpreting data
Constructing explanations and designing solutions

Disciplinary Core Ideas

MS-PS1.A: Structure and Properties of Matter
MS-PS1.B: Chemical Reactions
HS-PS1.A: Structure and Properties of Matter
HS-PS1.B: Chemical Reactions
HS-LS2.C: Ecosystem Dynamics, Functioning, and Resilience
HS-ESS2.C: The Roles of Water in Earth’s Surface Processes
HS-ESS3.C: Human Impacts on Earth Systems

Crosscutting Concepts

Cause and effect
Scale, proportion, and quantity
Systems and system models
Energy and matter
Stability and change

Performance Expectations

HS-PS1-1. Use the periodic table as a model to predict the relative properties of elements based on the patterns of electrons in the outermost energy level of atoms.
HS-PS1-2. Construct and revise an explanation for the outcome of a simple chemical reaction based on the outermost electron states of atoms, trends in the periodic table, and knowledge of the patterns of chemical properties.
HS-ESS3-6. Use a computational representation to illustrate the relationships among Earth systems and how those relationships are being modified due to human activity.

Sample Data



Answers to Questions

  1. Compare the initial color of the rainfall solution and the color of the filtrate. Is the pH of the filtrate higher or lower than the acid rain solution? Is it more acidic or more basic?

    The filtrate solution is more basic and has a higher pH than the “acid rain” solution.

  2. As the “acid rainfall” solution containing universal indicator passes through the demonstration tube, it changes color indicating a change in pH. Write out the balanced chemical equation for the “acid rainfall” solution reacting with the marble chips.

    H+(aq) + CaCO3(s) → HCO3(aq) + Ca2+(aq)

  3. The formation of bicarbonate ions creates a natural buffer system in lakes and streams. Write a balanced chemical equation for the buffering reaction of bicarbonate ions with acid. Describe the physical evidence supporting the presence of a buffer system.

    There is a buffer system present in the filtrate because when drops of “acid rain” are added the filtrate remains blue-green in color.

  4. A soil sample collected from a local stream was found to have high sand content. Is the water found in this stream likely to be more basic or acidic and why?

    The water sample collected from this stream is likely to be more acidic. Soils composed of silicates such as sand and granite have little acid-neutralizing capabilities. In order for the water in the stream to be neutralized the soil would have to contain carbonates.


The acidity of different bodies of water in a specific area can vary greatly. An increase in acidity is generally a result of pollution in the form of acid rain or snow. Acid rain is precipitation that has absorbed and reacted with compounds (mainly sulfur oxides and nitrogen oxides) in the atmosphere. The term acid rain is used to describe precipitation with a pH below 5.4.

Waters that are able to maintain a generally neutral pH do so largely because of the chemical makeup of the surrounding soil. Soils that are composed of carbonates, such as marble (limestone), are able to neutralize acidic solutions. Conversely, soils that are composed mainly of silicates, such as granite, have little or no acid-neutralizing capacity. When acidic rainfall flows over soils rich in carbonates, bicarbonate ions are formed and the rainwater runoff becomes more basic before entering the nearby body of water. The majority of lakes, rivers, and streams in the United States have pH values between 6.5 and 8.2. As the pH of water drops below this range, several negative events may occur. Physiological processes of many aquatic organisms can be disrupted or disabled. Toxic metals may be chemically released readily in waters at lower pH.

Acid rainfall reacts with limestone (calcium carbonate, CaCO3) to produce bicarbonate ions (HCO3), see Equation 1. This reaction decreases the hydrogen ion concentration in the acidic rainfall and increases the pH, as evidenced by the spectrum of color changes for the universal indicator solution from red to orange to green as it travels though the column in this demonstration.

The formation of bicarbonate ions creates a natural buffer system where the “lake water” in the filtrate can resist the acidifying effect of additional acid rainfall (Equation 2). This reaction is evident from the resistance of the filtrate to color change when more acid rain is added to it (step 5 in the Procedure).
The existence of limestone in lake beds enables the lake to initially resist changes in pH due to the formation of the buffer system.


This activity was adapted from Chemistry in the Environment, Flinn ChemTopic™ Labs, Volume 22; Cesa, I., Editor; Flinn Scientific Inc.: Batavia, IL (2006).

Next Generation Science Standards and NGSS are registered trademarks of Achieve. Neither Achieve nor the lead states and partners that developed the Next Generation Science Standards were involved in the production of this product, and do not endorse it.