KMT Mini-Lab

Purpose: To observe color changes in the chemical reactions of gases and to interpret these changes in terms of kinetic molecular theory.

1) Obtain a clean Petri dish and cover, dropper of Bromothymol blue indicator, and a template sheet for dot placement.
2) Place the smaller dish on the template page and place 1 small drop of Bromothymol blue indicator on each small dot on the template. There should be a total of 24 drops. Be sure the drops do not touch one another.
3) When ready, ask Ms. Mouton to please add 1 drop of NaOH and 1 drop of NH4Cl to the center of your dish. As soon as she adds the drops, put the cover on the dish and observe CAREFULLY AND WITH FOCUS. LOOK AT DETAILS! Questions:
1) Describe in detail the changes you observed in the drops of BTB over time. Draw pictures to illustrate the changes. Use colors.

2) Draw a series of pictures showing how one of the BTB drops might look over time if you could view the drop from the side. Use colors.

3) The BTB changed even though you added nothing to it. If the mixture in the center circle produced a gas, would this explain the change in the drops of BTB? Use kinetic theory to explain your answer.

4) Translate the following word equation into a balanced chemical equation: sodium hydroxide reacts with ammonium chloride to produce ammonia gas (NH3), water, and sodium chloride. Balance this equation. This is the rxn you just witnessed!

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