Chapter U2.19, Problem 5E

Interpretation Introduction

Interpretation : If a substance is capable of becoming a gas under normal conditions, would it be possible to smell it or not is to be explained.

Concept Introduction :

Humans are able to smell different molecules. Some molecules are small and some are large; some are polar and some are nonpolar. Some molecules are solids and some are liquids or gases.

Answer to Problem 5E

If a substance is capable of becoming a gas under normal conditions, it may not be possible to always smell it. All gases do not have smell. For example, nitrogen, oxygen, carbon dioxide, methane, etc do not have smell. Other factors also play a role in determining smell of a molecule such as polarity and size of molecules. Small molecules are gases but only if they are polar, they will have smell.

Heating may cause some large molecules to be smelled easily as they change to gas and as more molecules are present in air, it is easy to detect them.

Explanation of Solution

Molecules that can exist in gaseous form can be smelled easily as they can reach the receptor sites of our nose.Substances that one would expect to have a smell are those that are occur in gaseous form, have molecular covalent bonding, and are small polar molecules. Molecules which are not too large or not too small may be polar or non-polarand may also have smell.

All gases do not have smell. For example, nitrogen, oxygen, carbon dioxide, methane, etc do not have smell. Other factors also play a role in determining smell of a molecule such as polarity and size of molecules. Small molecules are gases but only if they are polar they will have smell.

Some large molecules that are solids or liquids at room temperature may undergo a phase change upon heating. Heating may cause their smell to be detected easily as more molecules are present in air.

Conclusion

Generally gases have smell but some gases do not have smell. Small polar molecules that are in gas form have smell.