Calculate the mass percentage of oxygen in dry air

0.23 = 23% O by mass

Explanation:

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We have the percentage data of each component in the air and its masses.

Nitrogen 0.78084 28.013

Oxygen 0.20948 31.998

Argon 0.00934 39.948

Carbon dioxide 0.000375 44.0099

Neon 0.00001818 20.183

Helium 0.00000524 4.003

Methane 0.000002 16.043

Krypton 0.00000114 83.80

Hydrogen 0.0000005 2.0159

Nitrous oxide 0.0000005 44.0128

Now we have to calculate a molar fraction.

(0.20948 * 31.998) = (0.78084 * 28.013)

+ (0.20948 * 31.998) + (0.00934 * 39.948) + (0.000375 * 44.0099) + (0.00001818 * 20.183) + (0.00000524 * 4.003) + (0.000002 * 16.043) + (0.00000114 * 83.80) + (0.0000005 * 2.0159) + ( 0.0000005 * 44.0128) = 0.23 = 23% O by mass

there are two significant figures.

chemical changes occur when a substance combines with another to form a new substance, called chemical synthesis or, alternatively, chemical decomposition into two or more different substances. these processes are called chemical reactions and, in general, are not reversible except by further chemical reactions. some reactions produce heat and are called exothermic reactions and others may require heat to enable the reaction to occur, which are called endothermic reactions. understanding chemical changes is a major part of the science of chemistry.