Learning target: I can record careful observations of a change, separate what I saw from what I think it means, and write a first explanation that says what evidence would confirm a new substance formed.
Read the description of the three jars and study the figure and the table. In Part A, write only what was seen or measured, not what it means. In Part B, take a snapshot of your current thinking; there is no penalty for a wrong choice. In Part C, write your first explanation. You will come back to this sheet at the end of the chapter and see how your explanation has changed.
You will need: This worksheet, Pencil, Optional teacher demonstration: three jars, copper sulfate solution, two clean iron nails, one copper strip, three thermometers, hand lens, goggles (copper sulfate irritates skin and eyes and is harmful if swallowed; the teacher handles it and disposes of it by district rules)
Ms. Okafor sets three identical glass jars on the front bench. She half-fills Jar 1 and Jar 3 with the same bright blue liquid, a solution of copper sulfate in water, and half-fills Jar 2 with plain water. Into Jar 1 she lowers a clean iron nail. Into Jar 2 she lowers a second clean iron nail from the same box. Into Jar 3 she lowers a thin strip of copper metal. A thermometer in each jar reads 22.0 °C. She asks the class to watch for twenty minutes and to write down anything that changes, and anything that does not.
| Jar | Solid placed in it | Liquid | What changed in 20 minutes |
|---|---|---|---|
| 1 | Iron nail | Blue copper sulfate solution | Nail turned red-brown; liquid paler and greenish near the nail; 22.0 °C to 23.5 °C; a few red-brown specks on the bottom |
| 2 | Iron nail | Plain water | No change seen; nail still shiny; water clear; 22.0 °C |
| 3 | Copper strip | Blue copper sulfate solution | No change seen; strip still shiny copper-colored; liquid still bright blue; 22.0 °C |
After twenty minutes Ms. Okafor lifts the nail from Jar 1, scrapes some of the red-brown layer onto a white dish, and lets the class look at it with a hand lens. The flakes are soft. When she presses one with the back of a spoon, it flattens into a thin shiny sheet instead of crumbling. She drops a few flakes into a cup of water; they sink and do not dissolve.
An observation names what a sense or a tool reported. Try these frames for Part A: "At 0 minutes the ___ was ___; at 20 minutes it was ___." "The thermometer in Jar ___ read ___." "In Jar ___ nothing changed: the ___ still looked ___." If your sentence contains the words because, so or must be, it is probably an explanation; save it for Part C.
Reference values: copper has a density of 8.96 g/cm³ and melts at 1085 °C; iron has a density of 7.87 g/cm³ and melts at 1538 °C; rust (iron oxide) has a density of about 5.2 g/cm³ and is a crumbly powder that does not flatten into a sheet. Using these numbers, design a two-step test a student could run on a pile of the red-brown flakes to decide among the four choices in q3. Say which result would support each choice and which choice the spoon test in the description already weakens.