What percentage composition of oxygen is h2o

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

=

2

×

M

H

M

H

2

O

×

100

%

=

2

×

1.0079 g/mol

18.015 g/mol

×

100

%

≈

11.19

%

H

Similarly for  

O

, we have

%

O

=

1

×

M

O

M

H

2

O

×

100

%

=

15.999 g/mol

18.015 g/mol

×

100

%

≈

88.81

%

O

Thus, the percent composition of water, by mass, is  

11.19

%

hydrogen and  

88.81

%

oxygen.

33.333% continued. In water the ratio is 2 H for every 1 O therefor the answer is 1/3 aka 33.333% continued.

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