Will mixing a solution of a cation and one of an anion always form an insoluable ionic compound?

Question

Please help me to understand this! thanx!

Answer 1

In a solution, the net charge for all anion and cation must add up to zero. A solution of only cation or only anion does not exist.

Answer 2

I think you may have become confused by looking at ionic equations, which only show the important ions, i.e., the ones undergoing a change. For instance, combining solutions of sodium silicate and magnesium sulfate,
Mg²⁺ + SiO₃²⁻ → MgSiO₃
the only ions of interest are magnesium and silicate, because they combine to precipitate out of solution. There is no sodium sulfate, only a solution of sodium ions and sulfate ions, until you evaporate the solution and crystallize it out. That doesn't mean the ions aren't there—they just aren't significant.

That's probably why introductory chemistry courses usually deal with less correct non-ionic equations, like
Na₂SiO₃ + MgSO₄ → MgSiO₃ + Na₂SO₄

You could just as easily write the meaningless equation
NaCl + KBr → NaBr + KCl
The reason it's meaningless is that a solution of sodium and potassium cations and bromide and chloride anions is just a solution of sodium and potassium cations and bromide and chloride anions. There is no precipitate (unless both solutions are saturated to begin with and the least soluble salt precipitates out), so the chloride doesn't belong to the sodium any more than it belongs to the potassium.

So the short answer to your question is no. And as someone else answered, there is no such thing as a solution of a cation without an anion, or vice versa.

Answer 3

No. There are a few things you have to take into account, such as the change in entropy and enthalpy required for the reaction to take place. Use the Gibbs Free Energy equation. Then, you have to worry about the solubility factor of the product, the Ksp. I don't completely remember how to calculate that, but I'm sure you can find a table of values. Although you are correct that if there is a reaction, an ionic compound will be produced, but you can't forget about the other half of your cations/anions. They don't simply disappear.

Answer 4

You can't make a solution of a "cation" and a solution of an "anion". Each solution has one of each. Mixing solutions does not necessarily cause an insoluble ionic compound to form. For instance, you can take a solution of NaCl and a second solution of KBr, and mix them together. Then you have all 4 ions in solution.