Question

How to determine what compound has the highest percent by mass of hydrogen?
For example of these compounds:
(A) $ HCl $
(B) $ {{H}_{2}}O $
(C) $ {{H}_{2}}S{{O}_{4}} $
(D) $ {{H}_{2}}S $
(E) $ HF $

Answer 1

Hint :We know that the mass percentage of any element in a compound or a molecule is hundred times the mass of the element which is further divided by the total mass. To calculate the mass percentage of any substance in the compound we can use the following formula:
 $ \dfrac{MassOfElement}{MassOFCompound}\times 100. $ We can also find the empirical formula of the compound if we are able to calculate its mass composition.

Complete Step By Step Answer:
To convert it to empirical formula the steps are that firstly get the mass of each element of the compound in grams. Then find their respective number of moles. Then divide each element number of moles by the smallest number of moles. Then convert them to whole numbers and put those numbers as the subscript in the empirical formula.
 $ MassPercent(H)=\dfrac{Mass(H)}{MassCompound}\times 100 $
Divide mass of hydrogen in each compound by the molar mass of the compound along with multiplying by $ 100. $ In calculations below, we have to take rounded masses to whole numbers. Also, numerators are mass of hydrogen in compounds in grams, as well as denominators are the molar masses of compounds in grams.
 $ HCl;\dfrac{1}{36}\times 100=2.8%H $
 $ {{H}_{2}}O;\dfrac{2}{18}\times 100=11.1%H $
 $ {{H}_{2}}S{{O}_{4}};\dfrac{2}{98}\times 100=2.0%H $
 $ {{H}_{2}}S;\dfrac{2}{34}\times 100=5.9%H $
 $ HF;\dfrac{2}{21}\times 100=9.5%H $

Note :
So if one has found the mass percentage of the element in the compound then we can find the empirical formula of that compound too. The empirical formula is the simplest whole number ratio of each type of the atom in the compound. It can be the same as that of the compound formula but not always.