Question #7a4c6
1 Answer
Explanation:
To obtain the molecular formula of this unknown compound, we first need to know the mole ratio between carbon and hydrogen.
We are only given the mass percentages of carbon and hydrogen. We don't know how many grams how much of the compound we actually have, so let's assume that we have
Carbon:
#88.8%# of#"100 g = 88.8 g"# Hydrogen:
#11.2%# of#"100 g = 11.2 g"#
We have
The Periodic Table of Elements indicates that the molar mass of carbon is about
#"88.8" cancel("g C") xx "1 mol C" / ("12.0" cancel("g C")) = "7.40 mol C"#
#"11.2" cancel("g H") xx "1 mol H" / ("1.0" cancel("g H")) = "11.2 mol H"#
We now know that there are
#"C"_7.40"H"_11.2#
But this doesn't look like a formula at all--the subscripts need to be integers. Usually you have to play around with the numbers until you get nice integers.
Let's divide both subscripts by
#"C"_1"H"_1.51#
Okay, we're close!
#"C"_2"H"_3#
So, the empirical formula of this compound is
Now we need to find the molecular formula. The molar mass of
Since