Question

If 1.0 g of hydrogen reacts completely with 19.0 g of fluorine, what is the percent by mass of hydrogen in the compound that is formed?

Answer 1

`"Well, 5%.......by mass......"`

Explanation:

With all the problems, a stoichiometric equation is the prerequisite:

`1/2H_2(g) + 1/2F_2(g) rarr HF(g)`

As specified, you have stoichiometric equivalents of dihydrogen and difluorine. Why?

And so `"percentage by mass hydrogen"`

`="Mass of hydrogen"/"Mass of hydrogen fluoride"xx100%`

`(1*g)/(20*g)xx100%=??%`

And thus `20*g` of hydrogen fluoride, which was the combined mass of the reactants, will result from stoichiometric reaction.