Classify each of these statements as always true, AT, sometimes true, ST, or never true, NT. ___ 1. A mole of a pure substance contains 6.02 x 1023 atoms. _ 2. The representative particle of a compound is a molecule. _ 3. A mole of CCl4 is composed of one atom of carbon and 4 atoms of chlorine. _ 4. One mole of gas occupies 22.4 L _ 5. The formula of methane is CH4. If methane contains 75% carbon, then 100 grams of methane contains 25 grams of carbon. _ 6. The formula for methane CH4 is both an empirical and molecular formula. ___ 7. The empirical formula of C6H12O6 is C2H4O2.

This is so because a mole of a pure substance contains that number of atoms at any point in time. The only criterion needed there is if the compound is pure or not.

2. NT.

3.AT

IN CCl4, we have one atom of carbon and 4 atoms of chlorine.

4. ST

This is only true in some instances and not at all times. The relation is only true at s.t.p. It does not hold at other conditions which are not s.t.p

5. NT

Methane contains 75% carbon. It is only right that 100gm methane would contain more than what the hydrogen would have as it has a higher percentage by mass and hence the 25gm is wrong.

6. AT

YES. The molecular formula of methane is also it's empirical formula

7. ST

This is not always true as we have more than one way in which the outside multiple n can multiply the inner numbers to yield the molecular formula. In the case quoted above, n = 3. Analysis can also show that n = 6 in which case the empirical formula would be CH2O.