1. Air contains mostly nitrogen (78%) and oxygen (21%). It also contains other gases, including carbon dioxide and helium, and various pollutants (both gases and solids). Write a brief explanation about why air is a mixture, whether it is homogeneous or heterogeneous, and how it can be separated into its components.

Question

1.	Air contains mostly nitrogen (78%) and oxygen (21%). It also contains other gases, including carbon dioxide and helium, and various pollutants (both gases and solids). Write a brief explanation about why air is a mixture, whether it is homogeneous or heterogeneous, and how it can be separated into its components.

rushwr · Answer

Air is a mixture of gases (and some dust) because the gases (oxygen, nitrogen, carbon dioxide, etc.) do not combine chemically into other compounds. Just like a mixture of salt & pepper doesn't combine into some other thing. 
The mixture is homogenous if it consists only of gases. If dust is mixed in the mixture is heterogeneous (dust is solid matter, gas is gas) A heterogenous mixture is one of different types of matter. 
Separating one gas from the other is different for each gas and a complicated matte

rushwr · Answer

matter*

mathmate · Answer

For the second part, read: http://www.bbc.co.uk/schools/gcsebitesize/science/edexcel_pre_2011/oneearth/usefulproductsrev2.shtml

anonymous · Answer

@rushwr so its heterogeneous because of the dust? Thank you for your detailed answer btw.