What is the percent composition of oxygen in water?

Answer 1

Nearly all the gas in the earth's atmosphere is either nitrogen (in the form of N2) and oxygen (O2). According the CRC Handbook of Chemistry and Physics (1997 edition), on average the composition dry air (water content excluded from the measurements) is:

Nitrogen -- N2 -- 78.084%

Oxygen -- O2 -- 20.9476%

Argon -- Ar -- 0.934%

Carbon Dioxide -- CO2 -- 0.0314%

Neon -- Ne -- 0.001818%

Methane -- CH4 -- 0.0002%

Helium -- He -- 0.000524%

Krypton -- Kr -- 0.000114%

Hydrogen -- H2 -- 0.00005%

Xenon -- Xe -- 0.0000087%

Ozone -- O3 -- 0.000007%

Nitrogen Dioxide -- NO2 -- 0.000002%

Iodine -- I2 -- 0.000001%

Carbon Monoxide -- CO -- trace

Ammonia -- NH3 -- trace

Note that free oxygen atoms (atoms that are not part of a molecule) did not even merit mention as a trace component. The vast majority is locked up in O2 with a tiny additional amount in CO2. Together they compose 20.979% of the molecules in the atmosphere and approximately the same percentage of the atoms in the atmosphere. When you include water (H2O) vapor in the calculations, the percent of oxygen in the atmosphere increases slightly.

Of course those are all figures for the atmosphere as a whole. The composition of the stratosphere where the "ozone layer" occurs is a little different. Water vapor content in the stratosphere is very low. Typical concentrations are in the range of 2-6 ppm (parts per million) compared to 1,000-40,000 ppm in the lower troposphere and 100 ppm in the upper troposphere. Ozone can reach as high as 20 ppm (0.0020%) but that is at the expense of O2 so the total amount of oxygen atoms remains constant.

Answer 2

In water there are two molecules of hydrogen and one molecule of oxygen.

So about 1/3 of the compound is made up of oxygen. However, if it were to be based on atomic weight, the answer would be different. Based on the Atomic Mass of each molecule (oxygen being about 15.9994 and hydrogen about 1.0079) then oxygen makes up about 89% of the water molecule's mass.

Answer 3

33.3% of the [number of] atoms are oxygen.

Answer 4

It's about half. But normally you dont measure chemicals like that. It's H2O (Hydrogen=2 atoms for every 1 atom of oxygen). However, Oxygen atoms are much bigger.

Answer 5

H2O has two hydrogen and one oxygen. Therefore two out of three molecules are hydrogen, or 66.6666666.... percent hydrogen, and 33.33333333.... percent oxygen.

Answer 6

92.8% Oxygen

Answer 7

88.81%