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The chemical form the we found in less video is called the empirical formula the empirical formula
is the simplest ratio
of the elements that make up the formula in this case the simplest ratio is three carbons for every eight Hydrogens
the actual formula may not be as simple as three carbons and three Hydrogens and may have 30 carbons and 80 Hydrogens but based on
the ratio the simplest 1C3H8 is although we know what this point
to find the true formula which is also called the molecular formula
we need to know the substance is actual molar mats and this is done by a different set of experiments so typical problem
will tell you for example
the molar mass is known to be this number two and 21 g per mole
we want a find the molecular formula
and what we know is the molecular formula will always be an energy are multiple of the simplest or the empirical formula
so with these numbers
will were looking for is what is the scaling factor
that will scale up the simplest ratio
to the actual ratio and you find this scaling factor
by knowing the molar mass of the molecular formula
divided by the molar mass
of the empirical formula
two earned 21 g per mole is
the molar mass of the true substance
in pure all formula remember 1C3H8
seeking calculate the molar mass using the periodic table three moles of carbon plus eight moles of hydrogen
fusion 44.11 g
per mole
these numbers should give you a ratio of feud everything correctly that is a small hole number and in this case you get a whole number five
so that tells you that this C3H8
has to be multiplied by five to give you the final answer of C15
H40
this is the true or molecular formula
and see 3H8 is simply to empirical formula