Question

next, the teacher adds zinc granules to the test tube and places the stopper back on top. first, bubbles are seen forming in the liquid in the test tube. next, bubbles form in the soap solution. the teacher notes that the previously room - temperature test tube has become very warm to the touch. as the bubbles leave the soap solution, the teacher holds a candle nearby. when the bubbles filled with hydrogen are near the flame, the heat initiates a reaction between the hydrogen in the bubbles and the oxygen in the surrounding air. the bubbles immediately catch fire and release a loud popping sound. the picture shows the bubbles. which observation provides the best evidence that the hydrogen and oxygen react? a. bubbles form in the test tube after the zinc granules are added to it. b. a large amount of heat and light is released when the bubbles pop. c. as the bubbles leave the soap solution, the teacher holds a candle nearby. d. after bubbles form in the soap solution, the test tube becomes warm to the touch.

Explanation:

A chemical reaction is indicated by signs such as heat/light release, color - change, gas production etc. When hydrogen and oxygen react, it is an exothermic reaction. The release of a large amount of heat and light when the bubbles (containing hydrogen) pop is a clear sign of a chemical reaction between hydrogen and oxygen. Bubbles forming in the test - tube (A) just shows gas production from the reaction of zinc with the liquid, not the reaction between hydrogen and oxygen. Holding a candle nearby (C) is just the initiation step, not evidence of the reaction itself. The test - tube becoming warm (D) could be due to the reaction of zinc with the liquid, not necessarily the hydrogen - oxygen reaction.

Answer:

B. A large amount of heat and light is released when the bubbles pop.