For a lab in school we had to mix together sodium carbonate and calcium chloride and had that go through a filter, finally ending with our final product of calcium carbonate (chalk), my question is that we have to do a graph and the graph shows that as the mass of calcium chloride increases, the mass of the calcium carbonate stays nearly the same (plateau's) WHY IS THAT?
Ca^2+(aq) + CO3^2-(aq) ==> CaCO3(s)
The net ionic equation is shown above. As the Ca^2+ is increased it reacts with carbonate ion and the CaCO3 is increased. At some point, the last of the carbonate is gone (since none is being added); therefore, no matter how much more Ca^2+ is added (from CaCl2), no more CaCO3 can be produced.
The plateau observed in the graph, where the mass of calcium carbonate remains nearly the same despite increasing the mass of calcium chloride, can be explained by the concept of limiting reactants in a chemical reaction.
In a chemical reaction, reactants combine to form products. The amount of product formed is determined by the reactant that is exhausted first, which is known as the limiting reactant. The other reactant is present in excess and, therefore, does not contribute to the increase in product formation.
In your case, sodium carbonate and calcium chloride react to form calcium carbonate. The balanced chemical equation for this reaction is:
Na2CO3 + CaCl2 -> CaCO3 + 2NaCl
From the equation, you can see that the mole ratio between sodium carbonate and calcium carbonate is 1:1. This means that, ideally, if you have an equal number of moles of sodium carbonate and calcium chloride, you should form an equal mass of calcium carbonate.
However, if you have an excess of calcium chloride, it will be the limiting reactant. This means that even if you increase the mass of calcium chloride, there will not be enough sodium carbonate to react with it. Therefore, the mass of calcium carbonate formed will not change significantly since the sodium carbonate is the limiting reactant determining the amount of product formed.
As a result, the graph shows a plateau in the mass of calcium carbonate as the mass of calcium chloride increases because the reaction has reached its limiting reactant, and adding more calcium chloride does not affect the amount of calcium carbonate produced.