How would you determine the empirical and molecular formula for hydrogen peroxide, which is 5.94% H and 94.06% O and has a molar mass of 34.01 g/mol?

The molecular formula is ##"H"_2"O"_2"##.

Since the percentages add up to 100%, we can assume that we have a 100-g sample, which will allow us to convert the percentages into grams.

##"H":####5.94%=>"5.94 g"## ##"O":####94.06%=>"94.06 g"##

Determine Moles of Each Element

First we need to determine moles of H and O by dividing their given masses by their molar masses (atomic weight on the periodic table) in g/mol.

##"H":####5.94cancel"g H"xx(1"mol H")/(1.00794cancel"g H")="5.89 mol H"##

##"O":####94.06"g O"xx(1"mol O")/(15.999"g O")="5.88 mol O"##

Determine and Empirical Formula

Since the number of moles for H and O are equal, ratios are 1.

The empirical formula is ##"HO"##

Determine the molecular formula.

The empirical formula mass is ##(1xx1.00794"g/mol")+(1xx15.999"g/mol")="17.007 g/mol"##

The molecular formula mass is ##"34.01 g/mol"##. To get the multiplication factor, divide the molecular formula mass by the empirical formula mass.

##"Multiplication factor"=(34.01"g/mol")/(17.007"g/mol")="2.000"##

To get the molecular formula, multiply the subscripts of the empirical formula times 2.

The molecular formula is ##"H"_2"O"_2"##.