Lab / experiment Grade 9 Science

Chalkwell's Karst Springs: A Limestone Dissolution Lab

A grade 9 lab where students measure chalk mass loss in three solutions, then use spring flow and hardness to calculate the limestone a fictional karst aquifer removes.

Grade: Grade 9
Subject: Science
Material: Lab / experiment
Time: 60 min
Prep: Moderate prep
Materials: Calcium carbonate chalk, 3 similar pieces per group (check the label, since dustless chalk is often calcium sulfate; limestone chips or plain calcium carbonate antacid tablets work as substitutes), Balance reading to 0.01 g, 1 per group or shared, Three clear 250 mL cups per group, labeled A, B, and C, Distilled water, 100 mL per group, Plain carbonated water, 100 mL per group, White vinegar, 100 mL per group, Graduated cylinder, 1 per group, pH test strips, 3 per group, Forceps or tongs, paper towels, and a timer, Safety goggles for every student

Standards

HS-ESS2-5 NGSS

Plan and conduct an investigation of the properties of water and its effects on Earth materials and surface processes.

How this material aligns: Procedure steps 3 through 6 and analysis items 2 through 5 have students test how acidified water dissolves calcium carbonate, the chemical weathering investigation this standard names.

All materials for HS-ESS2-5 →

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This material is in the public domain (CC0) and may be copied, edited, and shared freely, without attribution. Updated 2026-07-23.

Objectives

Students will measure the mass lost by calcium carbonate in solutions of different acidity.
Students will calculate percent mass loss and a dissolution rate from measured masses.
Students will connect laboratory dissolution to the hardness and rapid response of a karst aquifer.

Vocabulary

Aquifer: An aquifer is an underground layer of rock, sand, or gravel that holds water in the tiny spaces between its grains. Wells reach down into aquifers to bring water up to the surface.

Also: karst, calcium carbonate, dissolution, hardness

Teacher overview

Rainwater picks up carbon dioxide from the air and the soil, which makes it slightly acidic, and that mildly acidic water slowly dissolves limestone. Over long spans of time the process opens cracks into conduits and caves, producing the landscape called karst, where water moves through open passages instead of seeping through pore spaces. This lab has students compare how quickly calcium carbonate dissolves in distilled water, in carbonated water, and in vinegar, and then apply the result to the fictional Chalkwell valley, where a limestone spring supplies a small town. Students frequently describe dissolving as the solid breaking into pieces that settle out; the mass measurements here show that the solid leaves the system entirely, carried away as dissolved ions that later register as hardness in the water.

Chalkwell's Karst Springs: A Limestone Dissolution Lab — Grade 9 Science

Name: ____________________________ Date: ______________

Procedure

Step 1. Put on safety goggles and keep them on for the whole investigation. Vinegar stings the eyes, so tell your teacher at once about any splash or spill. Do not taste anything in this lab.

Step 2. Label three clear cups A, B, and C. Using a graduated cylinder, measure 100 mL of distilled water into cup A, 100 mL of carbonated water into cup B, and 100 mL of white vinegar into cup C.

Step 3. Dip a pH strip into each cup, compare it against the color chart, and record the pH of all three liquids in your data table before adding anything else.

Step 4. Choose three pieces of chalk that are close to the same size. Blot each piece dry with a paper towel. Find the mass of each piece to the nearest 0.01 g and record it as the starting mass.

Step 5. Place one piece into each cup at the same moment and start the timer. For the first minute, watch each cup and record what you see, paying attention to bubbles and to cloudiness near the surface of the solid.

Step 6. After 15 minutes, lift each piece out with forceps, blot it dry using the same number of blots you used in step 4, and find its mass again. Record each final mass. Blotting the same way both times keeps trapped water from changing your results.

Step 7. Pour the liquids down the drain with running water unless your teacher directs otherwise, return the balance to zero, and wash your hands before leaving the station.

Data & Analysis

Cup	Liquid	pH	Starting mass (g)	Final mass (g)	Mass change (g)	First-minute observations
A	Distilled water
B	Carbonated water
C	White vinegar

Which cup showed the greatest mass loss in your data, and what pH did you record for that cup?
Suppose a group recorded a starting mass of 4.20 g and a final mass of 3.78 g for the piece in vinegar. Find the percent mass loss for that piece.
Suppose the same group recorded 4.15 g and 4.13 g for the piece in distilled water. Find the percent mass loss for that piece.
The vinegar piece in item 2 lost 0.42 g over the 15-minute run. Find its dissolution rate in grams per minute.
Using your answers to items 2 and 3, explain what this investigation shows about how acidity affects the dissolution of calcium carbonate.
A spring in the fictional Chalkwell valley discharges 260 gpm. Convert that flow to MGD, using 694 gpm per MGD. Round to three decimal places.
Water from that spring carries 210 mg/L of hardness measured as calcium carbonate. Using pounds per day equals concentration in mg/L times flow in MGD times 8.34, find the pounds of dissolved mineral the spring carries away each day. Round to the nearest pound.
Karst passages are widened by the process you tested. Explain why water in a karst aquifer can carry contamination from a field or a parking lot to a spring in hours, while water in a sand aquifer may take years to travel the same distance.

From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.

Answer Key

Answer: Answers will vary with the samples used. Most groups find the greatest loss in cup C, the vinegar, and record the lowest pH there, commonly near 2 or 3, while cup B falls between the other two and cup A shows almost no change.
Answer: 10.0 percent. 4.20 g minus 3.78 g equals 0.42 g lost, and 0.42 divided by 4.20 equals 0.10, or 10.0 percent.
Answer: 0.48 percent. 4.15 g minus 4.13 g equals 0.02 g lost, and 0.02 divided by 4.15 equals 0.0048, or 0.48 percent.
Answer: 0.028 grams per minute. 0.42 g divided by 15 minutes equals 0.028 g per minute.
Answer: Accept any response that compares the two figures and draws the right conclusion. The vinegar piece lost about twenty times the percentage the distilled-water piece lost over the same 15 minutes, so a more acidic solution dissolves calcium carbonate much faster. Stronger answers note that distilled water dissolved a small amount as well, so acidity changes the rate rather than switching the process on.
Answer: 0.375 MGD. 260 gpm divided by 694 gpm per MGD equals 0.3746, which rounds to 0.375 MGD.
Answer: 657 pounds per day. 210 mg/L times 0.375 MGD equals 78.75, and 78.75 times 8.34 equals 656.8, which rounds to 657 pounds per day of dissolved mineral.
Answer: Accept any response describing open-channel flow. In karst, dissolution has widened cracks into conduits, so water runs through open passages with little filtering and very little contact with soil or grains. In a sand aquifer the same water must squeeze through small pore spaces, which slows it down and lets particles, bacteria, and some dissolved substances be trapped or broken down along the way. Faster travel with less filtering is why karst springs can turn cloudy within hours of a storm.

Differentiation

Support

Provide the starting masses already recorded for one group so students who struggle with the balance can still complete the percent-change calculations. Give a worked percent-change example with different numbers, and reduce the assigned analysis to items 1 through 5.

Extension

Have students design a follow-up test of one variable they did not control, such as surface area or temperature, writing a procedure that keeps every other condition the same. Ask them to predict, using the fictional Chalkwell spring data in items 6 and 7, whether warmer water would raise or lower the hardness the spring carries.

ELL supports

Pre-teach dissolve, mass, acidity, and hardness with a labeled sequence card showing solid chalk, bubbles, and clear water with dissolved ions drawn as small dots. Allow observation entries in the data table to be short phrases or sketches, and provide a sentence frame for item 5: "The piece in vinegar lost ___ than the piece in distilled water, which shows that ___."