Help please! I have a chemistry test tomorrow on net ionic equations, and my teacher gave us a review sheet. I did the review sheet and checked my answers, but I saw something I did not understand....

Help please! I have a chemistry test tomorrow on net ionic equations, and my teacher gave us a review sheet. I did the review sheet and checked my answers, but I saw something I did not understand. Barium Sulfate reacting with Sodium Sulfate = no reaction in a net ionic equation and the reason is "common ion effect". What does this mean? I would think that sulfate from the sodium would combine with the barium to form a precipitate.

Expert Answers
jerichorayel eNotes educator| Certified Educator

Barium sulfate reacting with another sulfate such as that of sodium sulfate will have no reaction due to common ion effect. To better explain this, let us rewrite the equation:

`BaSO_4 + Na_2SO_4 -> no reaction`

Doing the ionic equation:

`BaSO_4 (s) + 2 Na^+ (aq) + SO_4^(2-) (aq) -> no reaction`

The common ion effect is the presence of both sulfate (`SO_4^(2-)` ) in both compounds. There is no reaction because there are no new products that will be formed. 

If we notice the nature of two compounds in the solution, barium sulfate is expressed as solid `(s)` in the solution. This means that barium sulfate is sparingly soluble in water making it more stable as a molecule than ionic. On the other hand common ion effect can reduce the solubility of sparingly soluble species such as barium sulfate however it won't change the reaction.