Video Transcript
Sodium carbonate can be prepared in
the laboratory by passing carbon dioxide gas through a hot solution of sodium
hydroxide. What is the balanced equation that
describes the preparation?
Let us first explain what happens
as chemists pass carbon dioxide gas through a hot sodium hydroxide solution. The diagram represents a very
simplified image of the reaction. We know that carbon dioxide gas and
an aqueous solution of sodium hydroxide are reacted together. So we know that these two species
must be on the reactant side of the chemical equation to the left of the arrow. We are told that the reaction
prepares the salt sodium carbonate and the second product is water. Sodium carbonate and water are
products and should be to the right of the arrow. As a water-soluble salt, sodium
carbonate will be dissolved in liquid water.
Now that we have deduced the
reactants and products of this reaction with their state symbols, we can write the
chemical equation of this reaction. A sodium hydroxide solution
contains sodium one plus cations and hydroxide polyatomic anions with the chemical
formula OH1−. For the compound to have a neutral
charge overall, the chemical formula for sodium hydroxide would contain one sodium
cation present for every one hydroxide anion, giving us NaOH.
The gas carbon dioxide has the
chemical formula of CO2. Sodium carbonate, like sodium
hydroxide, will contain sodium cations. It will also contain carbonate
anions which have the chemical formula of CO32−. For the compound to be neutral
overall, there must be two sodium cations present for every one carbonate anion. This gives us a chemical formula of
Na2CO3. Finally, we will write the chemical
formula for water, which is H2O. Since heat was applied to generate
a hot solution of sodium hydroxide, we can indicate this with the 𝛥 symbol above
the reaction arrow.
Now, in order to make sure the
chemical equation is balanced, we must be sure each type of atom appears in the same
amount in the reactants and the products. The equation is not currently
balanced as there are different numbers of sodium, hydrogen, and oxygen atoms in the
reactants and products. We need a stoichiometric
coefficient of two in front of NaOH to balance this chemical equation. Now, all elements are in equal
number in the reactants and products.
Therefore, the balanced equation
for the preparation of sodium carbonate by passing carbon dioxide gas through a hot
solution of sodium hydroxide is two NaOH aqueous plus CO2 gas react to form Na2CO3
aqueous plus H2O liquid.
