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.

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 matter.

 Air is a homogeneous mixture of gases.

Explanation:  Mixture is a composition in which 2 or more substances are present together without making a chemical bond or a chemical compound between them.

Thus Air qualifies itself as mixture because there are several number of gases present in different composition and different proportions. These gases do not combine with each other to form a chemical compound between them.

Homogeneous mixture is the mixture in which the phase of the mixture is just single phase and it is not possible to separate the components. Thus Air is a homogeneous mixture and its component can never be separated because it forms a single phase.

the law of conservation of mass states that in a chemical reaction, the total mass of reactants is equal to the total mass of products. because atoms are only rearranged in a chemical reaction, there must be the same number of sodium atoms and chlorine atoms in both the reactants and products

answer by yourhope:

how do models compare to real-world objects?

d. most models represent a real-world object in a simpler way.

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