Evidence of chemical reactions Transitional Reasoning Download PDF

Questions

1. 1.

   In a laboratory investigation on changes in matter, a student conducts four separate procedures: boiling liquid ethanol on a hot plate, dissolving granulated sugar into warm water, blending yellow dye with blue dye to produce a green liquid, and combining two clear, room-temperature aqueous solutions that immediately form an opaque solid settling at the bottom of the beaker. Based on the observable indicators of chemical change, which procedure provides conclusive evidence that a chemical reaction took place rather than a physical change?

   • A) Boiling liquid ethanol, because the rapid release of vapor bubbles confirms that chemical bonds were broken to form a new substance.
   • B) Dissolving granulated sugar, because the complete disappearance of visible solid particles indicates a chemical transformation.
   • C) Blending yellow and blue dyes, because the appearance of a green color is definitive proof of a chemical synthesis reaction.
   • D) Combining the two clear solutions, because the spontaneous formation of an insoluble precipitate indicates that a new chemical substance was produced.