Video Transcript
Which of the following is the
correct balanced equation for the reaction of sodium with oxygen? (A) Two Na solid plus O2 gas react
to produce two Na2O2 solid. (B) Two Na solid plus O2 gas react
to produce four Na2O solid. (C) Four Na solid plus O2 gas react
to produce two NaO2 solid. (D) Four Na solid plus O2 gas react
to produce two Na2O solid. Or (E) two Na solid plus O2 gas
react to produce two NaO2 solid.
Sodium can be reacted with oxygen
to form Na2O or sodium oxide. Alternatively, sodium can be
reacted with oxygen to produce Na2O2, sodium peroxide. NaO2, or sodium superoxide, can be
prepared by reacting sodium peroxide with oxygen under a high temperature and
pressure. So it is feasible that this product
is formed. We can work out which one of the
equations is correct by going through them in turn and checking to see if they’re
correctly balanced.
Let’s start with option (A). We can omit the state symbols as
they’re all the same. There are only two elements in
these reactions, sodium and oxygen. In this reaction equation, there is
only one reactant species containing sodium. This is the case for all of the
options. It has a stoichiometric coefficient
of two. So we can put a tally of two for
sodium in the reactants column. And there is only one
oxygen-containing species in the reactant side. It is oxygen gas, and it is the
same for all options (A) to (E). It has a subscript value of
two. So we can do a tally of two for
oxygen in the reactants column. We don’t need to change the tally
for oxygen in the reactants column for the other options as all options from (A) to
(E) have only one mole of oxygen gas as a starting material.
For the sodium present on the
product side, it has a subscript value of two and a stoichiometric coefficient of
two. If we multiply these values
together, we get a value of four. The case is the same for
oxygen. It has a subscript value of two and
a stoichiometric coefficient of two. We can multiply these values
together to get a value of four. We can see that neither sodium nor
oxygen are balanced. So the equation in option (A) is
incorrectly balanced, and it cannot be the answer to this question.
Option (B) is two Na plus O2 react
to produce four Na2O. Again, we have a value of two for
sodium on the reactant side. But on the product side, sodium has
a subscript value of two and a stoichiometric coefficient of four. If we multiply these values
together, we get a value of eight. So sodium has a tally of eight for
the product side. Oxygen doesn’t have a subscript
value, so we can assume it to be one. But it has a stoichiometric
coefficient of four, so oxygen has a tally of four on the product side. Again, the tallies for oxygen and
sodium aren’t balanced. So option (B) cannot be the answer
to this question.
Option (C) is four Na plus O2 react
to produce two NaO2. This time, sodium has a
stoichiometric coefficient of four for the reactant side. But on the product side, it has a
coefficient of two. So sodium only has a tally of two
in the products column. Oxygen, on the other hand, has a
subscript value of two and a stoichiometric coefficient of two. If we multiply these values
together, we get a value of four. So again, neither sodium nor oxygen
are balanced, and option (C) cannot be the answer to this question.
Option (D) is four Na plus O2 react
to produce two Na2O. Sodium on the reactant side has a
stoichiometric coefficient of four. So we can do a tally of four for
sodium in the reactants column. On the product side, sodium has a
subscript value of two and a stoichiometric coefficient of two. If we multiply these values
together, we also get a value of four. Oxygen on the product side doesn’t
have a subscript value but does have a stoichiometric coefficient of two. So we can do a tally of two for
oxygen on the product side. Sodium has a tally of four on the
reactant side and the product side. And oxygen has a tally of two on
the reactant side and the product side. So as both sodium and oxygen are
balanced, then the reaction equation must be balanced.
So it seems as though option (D) is
the answer to this question. But to confirm, let’s look at
option (E). Sodium on the reactant side has a
stoichiometric coefficient of two, just as it does on the product side. But the oxygen on the product side
has a subscript value of two and a stoichiometric coefficient of two. If you multiply these together, you
get a value of four. So although sodium is balanced,
oxygen is not. So option (E) cannot be the answer
to this question.
Therefore, the answer to the
question “Which of the following is the correct balanced equation for the reaction
of sodium with oxygen?” is (D): four Na solid plus O2 gas react to produce two Na2O
solid.
