2 Responses

1. Jennifer

   14|Mar|2008 1

   Hello. I would like to have a take at this question

   Air is a mixture because its constituents, nitrogen, oxygen, carbon dioxide, noble gases, water vapour are not chemically combined. This is because, at different places, the composition of air varies.

   Air can be separated by physical methods like fractional distillation whereby air is first cooled and compressed. Then, nitrogen having a lower boiling point of -196 degree Celsius gets distilled over first, followed by argon, oxygen. This explains why the boiling and melting point of air varies according to its composition.

   There is also no chemical formulae for Air unlike compounds.

   The reason why air is not an element is because an element is a pure substance that has only one type of atom whereas air has few types of atoms.

   Reply

2. sean

   15|Mar|2008 2

   Hi Jennifer.

   Good attempt at this question on Elements, Compounds & Mixtures.
   That is a good answer.

   Below will be my suggested answer to differentiate between Compounds & Mixture.
   It is based on SPEC.
   S – Separation
   P – Properties
   E – Energy Changes
   C – Composition

   Ans:

   Air is considered as a Mixture of different gases, and not as Elements or Compounds.

   S – Different fractions of gases in the air can be separated by physical means, e.g. Fractional Distillation

   P – Each of the gases has their own properties. E.g., Oxygen still support combustion and relights a glowing splint, Carbon Dioxide will continue to turn limewater cloudy.

   E – No Heat/Light are involved when the different gases come together to form air.

   C – Ratio of each fraction of gases can vary from place to place. E.g., at places where burning occurs, % of carbon dioxide is higher and % of oxygen is lower, etc

   Hope this helps.
   Sean

   Reply