Thursday, June 15, 2017

Air Composition

Dry air contains nitrogen 78.048%, oxygen 20.9476%, argon 0.9347%, carbon dioxide 0.0314%, hydrogen 0.00005%. The composition of gas mixture is expressed as volume percent. The remaining 0.01 percent is accounted for by traces of neon, krypton, helium, ozone and xenon.

Science: Is air a compound or a mixture?

Air is the mixture of gases. The composition of gas mixtures is always expressed as volume percent unless otherwise specified. For a mixture of given composition, the volume occupied by each individual component may be computed by knowing the total volume, the partial pressure of each component may be computed by knowing the total pressure and the number of moles of each component may be calculated by knowing the total number of moles percent.

In many calculations, including gas mixtures, it is desired to know pseudo (or average) molecular mass of a mixture. The mixture of gases known as air enters into so many engineering problems that it is desirable to know its composition and pseudomolecular mass. Dry air contains nitrogen 78.048%, oxygen 20.9476%, argon 0.9347%, carbon dioxide 0.0314%, hydrogen 0.00005%. The composition of gas mixture is expressed as volume percent. The remaining 0.01 percent is accounted for by traces of neon, krypton, helium, ozone and xenon.

For most engineering calculations, air is assumed to have a composition of 79% nitrogen and 21% oxygen with the principal minor constituent, argon, being considered to be nitrogen. Air will contain water vapor but the amount will depend on weather conditions. The pseudomolecular mass of air may be calculated to be approximately 29 lb-mass per lb-mole and this figure should be used in problems involving air.

The calculation to get the psedomolecular mas of air,

Air Composition            Molecular mass (lb-mass per lb-mole)

N2 78.048%                   28.02
O2 20.9476%                 32.00
CO2 0.0314%,                44.00
H2 0.00005%                 2.02
Ar 0.9347%,                    39.91

Pseudomolecular mass of air = (28.02 x 0.78084) + (32 x 0.209476) + (44 x 0.000314) + (2.02 x 0.0000005) + (39.91 x 0.009347)

= 28.969 ~ 29 lb-mass per lb-mole

1. A mixture.The difference between a compound and a mixture is primarily that a mixture can be separated through physical means. Since air is essentially just a collection of various gases, air is a mixture.

2. Air is known to be a type of mixture. The very air that we have in the planet is actually a mixture of various gases that are naturally present in the world. A lot of calculations were made in order to confirm this, and there is a decent explanation to this that might pique your interests as well.
The actual mixture of the component were calculated over and over again, but the results are not exact, rather estimated to be exact. The molecular mixture of the gases ultimately formed the air that we breathe. Take note that this type of air is still made up of oxygen, but it’s not just any ordinary type of oxygen as it contains various components that made it more breathable as well.
It’s said that air is known to be also made up of nitrogen, and most of its components are actually nitrogen – with oxygen providing at least 20% of it. Other components are a very small fraction of argon and an very, very tiny amount of hydrogen. Scientists are not sure if there are any other components mixed into the fresh air that we breathe, but these four elements are the main ones that made up the air that we have.

Compounds, on the other hand, are known to have a more fixed amount than mixtures – just like how we mix water with a flavoring that we want. Compounds always needed to be exact, and therefore, air is actually a mixture of various elements in a natural way, but also in a way where it’s perfect for us to breathe in and out.
A chemical compound is a chemical substance consisting of two or more different chemically bonded chemical elements, with a fixed ratio determining the composition.
The ratio of each element is usually expressed by chemical formula.
For example, water (H2O) is a compound consisting of two hydrogen atoms bonded to an oxygen atom.
The atoms within a compound can be held together by a variety of interactions, ranging from covalent bonds to electrostatic forces in ionic bonds.
A continuum of bond polarities exist between the purely covalent bond (as in H2) and ionic bonds.
For example H2O is held together by polar covalent bonds.
Sodium chloride is an example of an ionic compound.

3. Pure air is actually a solution of the gases in the relative ratios listed in many of the previous posts. It is also a mixture in a practical sense, since the air we actually breathe contains numerous very small particles of dust, other organic particles, water droplets, etc.

4. Air is a mixture, which is made up of different compounds (covalently bound molecules made up of different elements, such as water H2O), and elements (molecules  made of only one element, like O2, and H2 or individual atoms). To further complicate the name game, air is also a solution, which is a homogeneous mixture (all one phase, gaseous in this instance). A solution is a type of mixture.

5. Air is a mixture of elements such as Oxygen and Nitrogen and a mixture of compounds such as water and carbon dioxide. A mixture is something that can be separated through physical means. Air can be separated into its elements and compounds by fractional distillation.

6. The best reason I can think of for why we believe that air is a mixture is that freezing air slowly yields different liquids at different temperatures. Liquid nitrogen has a different boiling point than liquid oxygen. They also freeze at different temperatures. If air were only 1 compound, then air in its entirety would have a single boiling point and a single freezing point.

7. Air is a mixture/blend of several gases and water (moisture). Its composition may change based on the ambient conditions. It is because it can be separated to its components using separation methods. Air is Mixture of nitrogen, oxygen, argon and trace gasses.

8. It is a mixture of several compounds, mainly nitrogen and oxygen with bits of water vapour, carbon dioxide and argon, plus traces of many other gases.

Is a mixture of air and liquid air a pure substance?
1.Air itself is not a ‘pure substance’. Air is a mixture— primarily of nitrogen and oxygen, plus small amounts of a handful of other things (CO2, Argon, etc, etc). Anything that is a ‘mixture’ is by definition not a ‘pure substance’.
Thank you very much.

2.No, because relative proportions of oxygen and nitrogen differs in air (gaseous phase) and liquid air (liquid phase) in equilibrium.
Since, pure substance is homogeneous and invariable in chemical composition. Moreover relative proportion of chemical elements of substance is constant. Therefore, not a pure substance.


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