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Given the numerous chemical compounds found in dry air [compressed into a liquid] of a given volume [lets say $22.4$ L for simplicities sake] whose atomic weights far surpass that of water alone assuming water is $H_2 O$. Why does $22.4$ L of compressed liquid air weigh less than the same bucket of liquid water?

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    $\begingroup$ en.wikipedia.org/wiki/Density ? $\endgroup$
    – Kyle Kanos
    Jan 20, 2014 at 21:25
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    $\begingroup$ The bulk of the mass of water comes from the Oxygen. The bulk of the mass of liquid air comes from Nitrogen. Nitrogen weighs less than Oxygen. The symmetry of water molecules may also allow them to pack better in liquid form? $\endgroup$ Jan 20, 2014 at 21:25

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The answer has to be the density. A quick Wikipedia search gives the main components of air to be $78$% $N_2$, $21$% $O_2$, and $1$% $Ar$. Similarly, the liquid densities of these components (let's ignore temperature effects on density): $0.807$ g/mL, $1.41$ g/mL, and $0.140$ g/mL, respectively. We can add up each components' contribution to the overall density.

$$(0.78*0.807 \text{ g/mL})+(0.21*1.41 \text{ g/mL})+(0.01*1.40) = 0.940 \text{ g/mL}$$

The density of water? $1.00$ g/mL. Thus given equal volumes, the water will weigh more.

Source for physical values: Wikipedia

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