Video Transcript
The balanced equation for the
oxidation of an organic molecule is as follows. Two CH3OH plus O2 reacts to produce
two A plus two H2O. The total relative formula mass of
the products is 96. Identify what compound A is. The relative atomic mass of carbon
is 12, hydrogen is one, and oxygen is 16.
In order to identify compound A,
let us remember the law of conservation of matter. It states that atoms cannot be
created nor destroyed in a chemical reaction.
In order to help us solve this
problem, let us discuss that reactants are to the left of the reaction arrow and
products are to the right. The law of conservation of matter
means that the atoms on the reactant side will be equal to the atoms on the product
side. Now let us apply the law of
conservation of matter to this chemical equation to identify compound A.
Let us start by looking at two
CH3OH on the reactant side of the chemical equation. The coefficient of two means that
there are two molecules of CH3OH. Therefore, there are two carbon
atoms, eight hydrogen atoms, and two oxygen atoms in two CH3OH.
In O2, there are two oxygen
atoms. Therefore, on the reactant side,
there are two carbon atoms, eight hydrogen atoms, and four oxygen atoms. The same number and type of atoms
are needed on the product side to abide by the law of conservation of matter.
Now let us take a look at the
product side, where there are two H2O molecules. The coefficient of two in front of
H2O means that there are two water molecules. Therefore, four hydrogen atoms and
two oxygen atoms are accounted for.
When these atoms from the product
side are removed from the atoms on the reactant side, the number of atoms of the
compound two A is known. Therefore, we know that in two
molecules of A, there are two carbon atoms, four hydrogen atoms, and two oxygen
atoms. Since there are two molecules of A
in two A, the atoms from two A need to be divided in half to determine the atoms in
one individual molecule of A. Therefore, there is one carbon
atom, two hydrogen atoms, and one oxygen atom in compound A. And the formula for compound A is
CH2O.
This solution can be checked using
relative formula mass, which is the sum of the number of each type of atom
multiplied by the atom’s relative atomic mass. Relative formula mass is noted as
𝑀 r.
Let us go back to the question,
which tells us that the relative formula mass for the products is 96. To help us solve this problem, we
can set up an equation, where 96 is equal to the sum of the relative formula masses
for two A and two H2O. Now let us calculate the relative
formula mass for H2O and substitute it into our equation.
To help us with this task, we will
use the relative atomic masses or 𝐴 r for each element that are given to us in this
problem. The relative formula mass for H2O
is the sum of the number of each type of atom multiplied by the atom’s relative
atomic mass, 𝐴 r. So, for water, we will multiply two
hydrogen atoms by its relative atomic mass of one and one oxygen atom by its
relative atomic mass of 16. When we add the relative atomic
mass of hydrogen atoms, which is two, and the relative atomic mass of the oxygen
atom, which is 16, the relative formula mass for water is 18.
Now we can substitute the relative
formula mass of water into our equation. Now we can calculate the relative
formula mass for CH2O. So, for the relative formula mass
of CH2O, we will multiply one carbon atom by its relative atomic mass of 12, two
hydrogen atoms by its relative atomic mass of one, and one oxygen atom by its
relative atomic mass of 16. When we add the relative atomic
masses of carbon, which is 12; hydrogen atoms, which is two; and the oxygen atom,
which is 16, the relative formula mass for CH2O is 30.
Now we can substitute the relative
formula mass for CH2O into the equation. When adding the two relative
formula masses together of the two products, the sum is 96. Therefore, compound A is CH2O.
