Posted by Bryan on Monday, February 5, 2007 at 3:01pm.
Part B TrueFalse
Classify each of the statements as always true, sometimes true, or never true.
1.____ST______ one mole of any gas occupies a volume of 22.4 L.
2_____NT______ for a substance of known molar mass, the number of moles of a sample can be calculated from the mass of the sample.
3_____AT______ the volume occupied by one mole of a gas is dependent on the molar mass of the gas.
4______AT_____ the volume of a gas at STP can be calculated from the number of molecules of the gas.
2, 3 need rethinking.
ok on some. Poor on others. I don't want to fill in the blanks but I will write a paragraph on gases and mols.
The mass occupied by a mole of ANY gas at STP is 22.4 L and contains 6.02 x 10^23 particles. It will be some other volume at non standard conditions; therefore, 1 and 4 are ok but you may want to rethink 3.
The mols of a substance can be calculated from mols = grams/molar mass. This is always true.
i put alaways true for number 3. What about number 2?
The answer for 2 lies in what I wrote previously. "The mols of a substance can be calculated from mols = grams/molar mass. This is always true."
The asnwer to #2 also is contained in what I wrote earlier. "The mass occupied by a mole of ANY gas at STP is 22.4 L and contains 6.02 x 10^23 particles. It will be some other volume at non standard conditions; therefore, 1 and 4 are ok but you may want to rethink 3."
Number three: THe volume of a gas does not depend on the molar mass of the molecules.

Chemistry (Check)  Rosie, Monday, March 11, 2013 at 9:06pm
Regarding 2&3:
2, always true. For a substance of known molar mass, the number of moles of a sample can (always) be calculated from the mass of the sample.
The molar mass of O2 is 32.00 g. (This is the substance of known molar mass).
Let's say you have a sample of 16 g O2.
...This gives you the info to set up an equation:
16.00 g O2 X 1 mol O2/32.00 g O2 = 0.5 mol O2
And as for the 3rd question...actually I don't know exactly, but I think it's NT.
And I'm just a current Chem 1 student on this same curriculum. So don't just take my word because I'm a tad fuzzy on it myself. Nevertheless I hope this helped ya out a little.