How do you calculate the percent composition of water?

2 Answers
Neh Pandya
Apr 27, 2016

books

Explanation:

For water we have to calculate it % of Oxygen and % of Hydrogen

Its long calculation to do it here but this video will help

Truong-Son N.
Apr 27, 2016

Since water is #"H"_2"O"# (molar mass is #"18.015 g/mol"#), it implies we have a percent composition of #"H"# and one for #"O"#.

Given that chemical formula, we have two equivalents of #"H"#, for which we can use its molar mass, #M_"H" = "1.0079 g/mol"#. We also have one equivalent of #"O"#, for which we can use its molar mass, #M_"O" = "15.999 g/mol"#.

The percent composition (by mass) of #"H"# is written in terms of a unified ratio of the molar masses is

#%"H" = (2xxM_"H")/(M_("H"_2"O"))xx100%#

#= (2xx"1.0079 g/mol")/("18.015 g/mol")xx100%#

#~~ color(blue)(11.19% "H")#

Similarly for #"O"#, we have

#%"O" = (1xxM_"O")/(M_("H"_2"O"))xx100%#

#= ("15.999 g/mol")/("18.015 g/mol")xx100%#

#~~ color(blue)(88.81% "O")#

Thus, the percent composition of water, by mass, is #11.19%# hydrogen and #88.81%# oxygen.

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