Lab / experiment Grade 5 Science
Drummond Springs Hard Water: A Grade 5 Mixing Test
Teams stir Epsom salt and washing soda into cups of warm water to find out whether mixing two clear solutions makes a new white solid, as a softening plant does.
Objectives
- Students will test whether mixing two dissolved substances makes a new substance.
- Students will record what each cup looks like right after mixing and after ten minutes.
- Students will use the white solid as evidence that dissolved matter was still in the water.
Vocabulary
Key words: dissolve, hard water, softening, solid, evidence
Teacher overview
The well water in the fictional town of Drummond Springs is hard, which means it carries dissolved minerals that leave crusty spots on dishes and build up inside pipes. A softening plant takes those minerals out by adding a second substance that turns them into a solid the plant can settle and remove. This lab is a classroom version of that step: teams dissolve Epsom salt in water to stand for hard water, then stir in washing soda and watch for a white solid that was in neither cup before. The misconception the lab is built to correct is the idea that a dissolved powder is gone; cup A looks like plain water, yet the cloud that forms in cup B is evidence that the Epsom salt was there the whole time.
Procedure
Step 1. Put on safety goggles. Do not taste anything in this lab. Wash your hands when you finish.
Step 2. Washing soda is not the same as baking soda. Keep it out of your eyes. If any gets on your skin, rinse with water. Your teacher will hand out the powders.
Step 3. Label three clear cups A, B, and C with tape.
Step 4. Pour 100 milliliters of warm water into each of the three cups.
Step 5. Stir 1 teaspoon of Epsom salt into cup A. Stir 1 teaspoon of Epsom salt into cup B. Stir each one until the grains are gone. Cup C gets no Epsom salt.
Step 6. Look at all three cups. Write down what you see. All three should look clear.
Step 7. Stir 1 teaspoon of washing soda into cup B. Stir 1 teaspoon of washing soda into cup C. Cup A gets nothing new.
Step 8. Watch the cups for 2 minutes. Write down what happens in each one.
Step 9. Let the cups sit still for 10 minutes. Then look at the bottom of each cup and write down what you see.
Step 10. If your teacher gives you a filter and a funnel, pour cup B through the filter. Look at what stays on the paper.
Step 11. Pour the cups down the drain with plenty of running water. Throw away the filter. Wipe the table and wash your hands.
Data & Analysis
Fill in the table as you work.
| Cup | What is in it | Right after mixing | After 10 minutes |
|---|---|---|---|
| A | Water and Epsom salt | ||
| B | Water, Epsom salt, and washing soda | ||
| C | Water and washing soda |
- Which cup turned cloudy after the second powder was stirred in?
- Cup A held only Epsom salt, and cup C held only washing soda. Both cups stayed clear. What does that tell you about each powder on its own in water?
- The white cloud in cup B was not in the cup before you stirred. Is that good evidence that a new substance formed? Explain your thinking.
- You poured 100 milliliters of water into each cup. If you poured 40 milliliters out of cup B, how many milliliters would be left in cup B?
- One team says the white cloud is only powder that never dissolved. Describe one test you could run to check that idea.
- A real plant takes the white solid out of the water before the water goes to homes. Explain why an operator would want to remove 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: Cup B. It is the only cup that held both powders, and it turns milky white within seconds. Accept the team's own observation as long as it matches their table.
- Answer: Each powder dissolves in water by itself. The grains break into pieces too small to see, so each cup still looks clear even though the powder is still in there.
- Answer: Yes. A white solid appeared that was not in cup A, not in cup C, and not in cup B before the second powder went in, so mixing the two made something new. Accept any answer that names the new solid as the evidence.
- Answer: 60 milliliters. Start with 100 milliliters and pour off 40 milliliters: 100 - 40 = 60 milliliters left in the cup.
- Answer: Accept any workable test. Students may stir cup B longer or warm it to see whether the cloud dissolves the way the grains did in cup C, or they may add a spoonful of washing soda to plain water and confirm that it goes clear every time.
- Answer: The solid would settle in pipes and water heaters or make the water cloudy at the tap. Taking it out at the plant keeps the pipes clear and sends clean-looking water to homes.
Differentiation
Support
Pre-measure the water and the two powders into labeled paper cups for these teams, so they start at the stirring step. Give them a data table with the "What is in it" column already filled in and picture choices, such as clear, cloudy, or settled, to circle for each observation.
Extension
Have these teams repeat the test with cold water instead of warm water in cups A and B, keeping every other part the same, and describe any difference in how fast the cloud forms. Ask them to explain why an operator in the town of Drummond Springs would care about water temperature.
ELL supports
Pre-teach "dissolve," "cloudy," and "solid" by stirring a spoonful of salt into a cup of water as the class says each word. Provide a word bank of observation words, such as clear, cloudy, white, and settled, so students can label the table without writing full sentences.
Extensions
Ask students to look for hard-water spots on a faucet, a kettle, or a glass at home and sketch what they see. In a town with hard water like the fictional Drummond Springs, those spots are the same minerals that the plant tries to remove, left behind after the water evaporates.