Question #e0e87
1 Answer
Here's what I got.
Explanation:
The idea here is that you need to use the concept of mass conservation to determine how much silicon and hydrogen were present in your unknown compound.
More specifically, you need to use the fact that the mass of silicon that was present in the compound before the reaction took place will now be present in silicon dioxide,
Likewise, the mass of hydrogen that was present in the compound before the reaction took place will now be present in water,
This means that if you can determine how much silicon you get in
So, in order to find the percent composition of silicon in silicon dioxide, you need to know the molar mass of the compound and the molar mass of silicon.
#"For Si: " "28.09 g mol"^(-1)#
#"For SiO"_2: " 60.08 g mol"^(-1)#
Notice that one mole of
#(28.09 color(red)(cancel(color(black)("g mol"^(-1)))))/(60.08color(red)(cancel(color(black)("g mol"^(-1))))) xx 100 = "46.75% Si"#
This means that every
#31.27color(red)(cancel(color(black)("g SiO"_2))) * "46.75 g Si"/(100color(red)(cancel(color(black)("g SiO"_2)))) = "14.62 g Si"#
Now do the same for water. The molar masses of hydrogen and of water are
#"For H: " "1.00794 g mol"^(-1)#
#"For H"_2"O": " 180.15 g mol"^(-1)#
Now, notice that one mole of water,
#(color(red)(2) xx 1.00794 color(red)(cancel(color(black)("g mol"^(-1)))))/(18.015color(red)(cancel(color(black)("g mol"^(-1))))) xx 100 = "11.19% H"#
So, every
#18.72color(red)(cancel(color(black)("g H"_2"O"))) * "11.19 g H"/(100color(red)(cancel(color(black)("g H"_2"O")))) = "2.095 g H"#
So, you know that your original compound contained
#"14.62 g Si"# #"2.095 g H"#
Use its total mass to find the percent composition of each element
#"For Si: " (14.62 color(red)(cancel(color(black)("g"))))/(50color(red)(cancel(color(black)("g")))) xx 100 = color(green)("29% Si")#
#"For H: " (2.095color(red)(cancel(color(black)("g"))))/(50color(red)(cancel(color(black)("g")))) xx 100 = color(green)("4.2% H")#
I left the answers rounded to two sig figs.