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?

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Answer 1 · 2017-02-20T14:01:46

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

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.