Learning target: I can use measured properties (density, solubility in water, boiling point, flammability) and a reference table to argue which substance an unknown liquid is.
Read the scenario and the teacher's test record. Study the reference table of the five possible liquids. Answer the warm-up questions first; they will organize your evidence. Then write your Claim, Evidence and Reasoning in the boxes. A strong response uses specific numbers, says which candidates each piece of evidence rules out, and explains why more than one test was needed.
You will need: This worksheet, Pencil, Scrap paper for the ruling-out grid, Calculator (optional)
While cleaning the school makerspace, Ms. Dao finds a half-full plastic bottle with a faded label. The only readable words are 'clear liquid' and 'store away from heat.' Before she can decide how to dispose of it, she needs to know what it is. The makerspace supply list shows that only five clear liquids were ever ordered: water, isopropyl alcohol, acetone, glycerin and mineral oil. Ms. Dao runs four tests herself, behind a safety shield, and records the results. Students were not present for the flame test.
| Test | What was done | Result |
|---|---|---|
| 1. Density | Measured the mass of 25.0 mL of the liquid in a pre-weighed cup | 19.7 g for 25.0 mL |
| 2. Mixing with water | Added 5 mL of the liquid to 20 mL of water and swirled | Mixed completely; one clear layer, no separation after 10 minutes |
| 3. Boiling point | Heated 10 mL gently in a test tube with a thermometer in the vapor | Trial 1: 82.0 °C; Trial 2: 83.0 °C; Trial 3: 82.5 °C |
| 4. Flammability | Teacher touched a lit splint to a few drops on a watch glass | Caught fire at once; pale blue flame, hard to see |
| Liquid | Density (g/cm³) | Mixes with water? | Boiling point (°C) | Flammable? |
|---|---|---|---|---|
| Water | 1.00 | yes (it is water) | 100 | no |
| Isopropyl alcohol | 0.79 | yes, completely | 82 | yes |
| Acetone | 0.78 | yes, completely | 56 | yes, very |
| Glycerin | 1.26 | yes, completely | 290 | not easily |
| Mineral oil | 0.84 | no, forms a layer | above 300 | burns only when very hot |
On scrap paper, write the five candidates across the top and the four tests down the side. In each box write 'fits' or 'out' with a two-word reason (for example, 'out: too dense', 'out: wrong boiling point'). The one column with 'fits' in every row is your claim, and each 'out' is a piece of evidence you can copy into your CER with its number.
Ethanol (the alcohol in hand sanitizer) has a density of 0.79 g/cm³, mixes completely with water, boils at 78 °C and is flammable. Suppose it had also been on the supply list. Rewrite your Evidence section so that it rules ethanol out, and explain why a thermometer that reads only to the nearest 5 °C would have left the case unsolved. Then propose a fifth test that could separate isopropyl alcohol from ethanol, and say what you would need to look up before trusting it.