14. As students observe boiling water in a beaker on a hot plate, their teacher

Question

14. As students observe boiling water in a beaker on a hot plate, their teacher asks them what gas is contained within the bubbles that form. The first stucdent answers, hydrogen." Of the following teacher responses, which is the most appropriate? (A) Holding a lit match over the boiling water to immediately disprove the student's misconception Immediately saying the answer is (B) incorrect, then calling on other students until a correct answer is provided (C) Ignoring the first student and only acknowledging the student that provides the correct answer (D) Polling the class, then brainstorming with the students to design an investigation to determine the identity of the gas

Explanation / Answer

When water is boiled, it actually undergoes a transformation in its state from liquid to vapour(gas). That is why it is considered that the gas which is evolved is also primarily water, hence water vapour, which has a composition almost equivalent to that of the atmospheric vapour.

Therefore when the student says that the evolved gas is hydrogen, the best thing that the teacher can do is to hold a lighting matchstick above the boiling water so that if it goes off, then it can be confirmed that the gas which is evolved contains hydrogen specifically.

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