Ammonia is a gas with the following properties: It is colourless, it is less dense than air, it dissolves in water, and it has a strong odor. Sam needs to collect a sample of ammonia gas from an...

Ammonia is a gas with the following properties: It is colourless, it is less dense than air, it dissolves in water, and it has a strong odor.

Sam needs to collect a sample of ammonia gas from an experiment she is doing. She has glass jars, glass tubing, glass bowls and water available to her. Which option below shows the most suitable setup for her to collect the ammonia gas?

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t-nez | High School Teacher | (Level 3) Associate Educator

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Gas is usually collected by water displacement, but that's not a good choice for ammonia because of its solubility in water. Diagram C shows the best way to collect ammonia - by upward displacement. Since it's lighter it will remain in the top of the collection container and air will be displaced out the bottom. Since ammonia gas has a strong odor it would be best to perform this procedure in a fume hood. It's also a respiratory irritant. It will be hard to visually detect when the jar contains only ammonia and the air has been driven out, but one would know from the odor.

Methods a and b would both allow the gas to escape, and d would allow it to dissolve in the water present at the bottom. 

Another method of collecting lighter than air gases is to use a syringe with a plunger that moves outward from the pressure of the gas entering the syringe.

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