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Type
quick_poll
Options
A chemical change occurred because the color of the water changed.
A physical change occurred because the food coloring just mixed into the water and no new substance was made.
A chemical change occurred because the food coloring disappeared into the water.
A physical change occurred because the water got colder when it was stirred.
Question
A student stirs purple food coloring into a glass of water. The water turns purple. Which statement BEST describes what happened?
Teacher Notes
Why Correct: This is a physical change because the food coloring and water are simply mixing together — no new substance is formed. The color change is a result of the dye spreading through the water (diffusion), not a chemical reaction. The food coloring and water could theoretically be separated, and neither substance has transformed into something new.
Decision Guidance
50 To 80: A significant group is still relying on color change as their main clue. Do a quick side-by-side class comparison: hold up two examples — (1) food coloring in water and (2) baking soda + vinegar fizzing. Ask students to discuss with a partner: 'In which one was a NEW substance made?' Then anchor the rule: color change is a CLUE, not proof — we have to ask if a new substance formed.
Above 80: Most students understand that color change alone doesn't determine reaction type. Push their thinking deeper: show them a image of a rusting nail (color change + chemical change) and ask them to explain WHY that one IS a chemical reaction while the food coloring example is not. Have students write a 'rule' for how to tell the difference using evidence beyond color.
Below 50: Most students are using color change as their decision rule for chemical reactions. Reteach using a 3-column anchor chart titled 'Color Changed — But Was It Chemical?' with columns: Example / Did color change? / Was a new substance made? Walk through 3 examples together: (1) food coloring in water — yes/no = physical, (2) burning paper turning black — yes/yes = chemical, (3) mixing red and blue paint — yes/no = physical. Explicitly name the misconception: 'Color change is a CLUE, but it is NOT proof. We always have to ask: was something NEW made?'
Misconception Map
A Chemical Change Occurred Because The Color Of The Water Changed.: This reveals the core target misconception: students are using color change alone as their evidence for a chemical reaction. Research consistently shows that 5th graders treat any visible color change as a reliable indicator of a chemical reaction (Özmen, 2004; Nakhleh, 1992). Students need to learn that the KEY question is whether a NEW substance was formed, not whether the color changed.
A Physical Change Occurred Because The Water Got Colder When It Was Stirred.: This student has the right answer category (physical change) but is using incorrect reasoning. They may be guessing or relying on an irrelevant observation. While this student isn't showing the target misconception, they need support identifying VALID evidence for classifying changes.
A Chemical Change Occurred Because The Food Coloring Disappeared Into The Water.: This student may be confusing dissolving or mixing with a chemical reaction. They may think that when something 'disappears' or looks different, it has chemically changed. This is related to the misconception that dissolution is a chemical change — a well-documented error in elementary science (Driver et al., 1994).
Correct Answer
A physical change occurred because the food coloring just mixed into the water and no new substance was made.