In this experiment, Sofia mixed 100 g blue water with 100 g yellow water; it turned green, but the scale showed 200 g before and after. How is the observable change different from the weight change?
- The color changed, but the total weight stayed the same. (correct answer)
- The color changed, so the total weight must have changed.
- The color stayed the same, but the total weight changed.
- The color and the total weight both did not change.
Explanation: This question tests the ability to distinguish between observable changes (what you can see, feel, or detect) and changes in total weight (amount of matter present) (NGSS 5-PS1-2). Students must recognize that many observable changes occur without any change in total weight. When blue and yellow water mix to create green, there's a dramatic observable change in color—a completely new color appears that wasn't present before. However, all the water molecules from both solutions are still present, just mixed together, which is why the total weight remains 200 g (100 g + 100 g). Choice A is correct because it accurately states that the color changed (blue + yellow = green) but the total weight stayed the same (200 g), showing that color changes don't affect the amount of matter present. Choice B incorrectly assumes that because the color changed, the weight must have changed too, conflating visual changes with changes in the amount of matter. To help students distinguish observable changes from weight changes: Create a two-column comparison table. For color mixing: observable—new color appears; weight—NO change. Demonstrate that mixing doesn't make matter disappear—all the original particles are still there, just mingled together.