Lab / experiment Grade 3 Science
The Settling Jar Test at Cloverstock Creek: A Grade 3 Lab
A grade 3 lab in which teams shake three jars holding sand, garden soil, and potting mix, then score how fast each one clears at five, ten, and twenty minutes.
Objectives
- Students will run a fair test that changes only the kind of solid in the jar.
- Students will score jar clarity at three set times using the same card.
- Students will explain why a settling tank holds water for a long time.
Vocabulary
Key words: settle, clarity, trial, fair test, control, settling tank
Teacher overview
A settling basin at a drinking water plant is a large, quiet tank that gives heavy particles time to sink before the water reaches the filters, and how long that takes depends on what the particles are. This lab asks one testable question about that: does the kind of dirt in the water change how fast the water clears? Teams shake three jars that differ only in the solid added, then score each jar against a printed line card at five, ten, and twenty minutes. Cloverstock Creek in the title is a fictional stream standing in for any creek that carries sand from a bank, soil from a field, and light material from a garden, and the jar is a simple model rather than a real basin.
Procedure
Step 1 (safety). Do not drink any water used in this lab. Wipe up every spill right away. Wash your hands when the test is over.
Step 2 (label the jars). Tape a label on each jar. Mark one jar Sand. Mark one jar Garden Soil. Mark one jar Potting Mix. These stand for three kinds of dirt that wash into Cloverstock Creek.
Step 3 (add the water). Pour one liter of tap water into each jar. Check the mark at eye level. Every jar gets the same amount of water.
Step 4 (add the solid). Put two level spoons of play sand in the sand jar. Put two level spoons of garden soil in the next jar. Put two level spoons of potting mix in the last jar. Keep the spoon count the same for all three.
Step 5 (mix the same way). Screw the lids on tight. Shake each jar 20 times. Count out loud as you shake. Set all three jars down at the same moment.
Step 6 (start the clock). Start the timer as soon as the jars are down. Write your start time in the table. Do not move or bump the jars after this.
Step 7 (read the jars). Hold the clarity card behind a jar. Look through the water at the black line. Score the jar 0 if you cannot see the line, 1 if the line is faint, and 2 if the line is easy to see. Read all three jars at 5 minutes. Read them again at 10 minutes. Read them a third time at 20 minutes.
Step 8 (watch for failure points). Stop if a jar leaks or tips. Set that jar up again with the same water and the same two spoons, then start it over. Write down what went wrong.
Data & Analysis
Start time: ____
| Jar | Score at 5 minutes | Score at 10 minutes | Score at 20 minutes |
|---|---|---|---|
| Sand | |||
| Garden Soil | |||
| Potting Mix |
- Which jar had the highest score at 5 minutes?
- Which jar had the lowest score at 20 minutes?
- A team started its test at 10:05. The team read the jars again 20 minutes later. What time was that reading?
- Every jar got one liter of water. Why did that amount have to stay the same in all three jars?
- Name one other thing your team kept the same in all three jars.
- A settling tank at a water plant works like your jar. Should the water sit in the tank a short time or a long time? Use your scores.
- Did a jar leak, tip, or get a different number of shakes? Tell what went wrong and what your team did about it.
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: Usually the sand jar. Accept whichever jar the team's own table shows as highest at the five-minute reading. Sand grains are heavy and drop quickly, so that jar most often scores 2 first, though a hard shake can carry fine grains higher and delay it.
- Answer: Usually the garden soil jar or the potting mix jar. Accept whichever jar the team's table shows as lowest at twenty minutes. Tiny clay bits in garden soil can keep water cloudy for hours, and fine bits of peat can also tint or cloud the water, while sand clears first.
- Answer: 10:25. Start at 10:05 and count on 20 minutes, which brings the clock to 10:25.
- Answer: To keep the test fair. Accept any answer explaining that a jar with less water would look cloudier for the same amount of dirt, so the team could not tell whether the kind of solid or the amount of water changed the score.
- Answer: Accept any real control from the setup, including the same jar size, the same two spoons of solid, the same 20 shakes, the same clarity card, the same reading times, or the same table the jars rested on.
- Answer: A long time. Accept any answer that uses the team's own scores to argue that jars kept getting clearer between the five-minute and twenty-minute readings, so a tank that holds water longer sends cleaner water on to the filters.
- Answer: Accept any failure the team recorded, such as a leaking lid, a bumped table, a jar shaken a different number of times, or a spoon that was heaped instead of level. Accept any fix that put the jar back on equal terms, including starting that jar over, and accept a report of no failures from a team whose setup held.
Differentiation
Support
Pre-measure the liter of water and the two spoons of solid into labeled cups so these students begin at Step 5 with a ready setup. Give them a scoring sheet with the three jar names and the three time marks already printed, and let them circle a score word rather than writing the number. Reduce the readings to 5 minutes and 20 minutes.
Extension
Have these students run a second fair test that holds the solid at garden soil and changes only the shake count, using 5 shakes, 20 shakes, and 40 shakes. Ask them to predict the result first, keep the water at one liter, and then write which of the two tests would be more useful to an operator deciding how long a tank should hold water.
ELL supports
Pre-teach "settle," "clear," and "shake" by demonstrating one jar before teams begin, and post the three score words with a small drawing of the line card at each level. Provide the frames "The ___ jar was clearest at ___ minutes" and "We kept the ___ the same." Allow items 1 and 2 to be answered by pointing to the jar.
Extensions
Leave the three jars undisturbed until the next school day and have teams score them one last time, then compare that score with their twenty-minute reading. Ask students to write one sentence about what an operator gains by giving a tank more time, and one sentence about why a plant cannot simply wait a whole day for every batch.