# How many grams of H are there in 23.5 g of #H_2O#?

##### 1 Answer

#### Explanation:

One way to approach this problem is to determine the percent composition of hydrogen in water.

You know that one water molecule contains

one oxygen atomtwo hydrogen atoms

This means that *every mole* of water molecules will contain **2 moles** of hydrogen and **1 mole** of oxygen atoms.

To find the percent composition of hydrogen in water, use the molar mass of water and that of hydrogen

#(2 xx 1.00794color(red)(cancel(color(black)("g/mol"))))/(18.0153color(red)(cancel(color(black)("g/mol")))) xx 100 = 11.19%#

This means that **every**

#23.5color(red)(cancel(color(black)("g water"))) * "11.19 g H"/(100color(red)(cancel(color(black)("g water")))) = color(green)("2.63 g H"#

**Alternatively**, you can first find the number of moles of water in get in that

#23.5color(red)(cancel(color(black)("g"))) * ("1 mole H"_2"O")/(18.0153color(red)(cancel(color(black)("g")))) = "1.3044 moles H"_2"O"#

SInce one molecule of water contais 2 atoms of hydrogen, you will get

#1.3044color(red)(cancel(color(black)("moles water"))) * "2 moles H"/(1color(red)(cancel(color(black)("mole water")))) = "2.6088 moles H"#

Finally, use hydrogen's molar mass to find how many grams would contain this many moles

#2.6088color(red)(cancel(color(black)("moles"))) * "1.00794 g H"/(1color(red)(cancel(color(black)("mole")))) = color(green)("2.63 g H")#