Question

Which of the following samples will have the greatest volume at STP?

Answer 1

Answer:

• The second choice: 22 g He will have the greatest volume at STP

Explanation:

Following Avogadro's principle, under ideal condtions, the volume of the gases at the same conditions of temperature, and pressure, is proportional to the number of molecules.

Then, you can calculate the number of molecules for each of the gases to determine which is the sample with the greatest number of molecules and, hence, which will have the greatest volume at STP (standard temperature and pressure).

The formula to calcualte the number of molecules (in moles) is:

• n = mass in grams / molar mass

Then, since the mass is the same (22 g) for the four options, the result will be dependent on the molar mass: the gass witht the smallest molar mass will give the largest number of moles for 22 g, and will have the  greatest volume.

a) 22 g CO:

• Molar mass of CO ≈ 28 g/mol

b) 22 g He:

• Molar mass of He ≈ 4.0 g/mol

c) 22 g O₂

• Molar mass of O₂ ≈ 32 g/mol

d) 22 g Cl₂

• Molar mass of Cl₂ ≈ 71 g/mol

Conclusion: since He has the smallest molar mass, the sample of 22 g of He gas will have the greatest volume at STP.