At STP, which property can be used to differentiate between a 2.0-gram sample of oxygen, O2(g), and a 2.0-gram sample of helium, He(g)?

Regents Chemistry Exam January 2025 Question 5.

5.At STP, which property can be used to differentiate between a 2.0-gram sample of oxygen, O2(g), and a 2.0-gram sample of helium, He(g)?

(1) mass (3) reaction with sodium

(2) temperature (4) phase of each sample

Solution:

Let's look at the answers first. Since both samples are 2 grams each, mass would not be a differentiating factor. Both samples are at STP (standard temperature and pressure). Therefore, they both have the same temperature as well, eliminating choice 2. Finally, both samples are in a gaseous phase as indicated by (g) next to each. Choice 4 is out as well. Choice 3, reaction with sodium, is the correct answer choice.

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