Indicate a potential reaction between electrolyte solutions where NOTHING happens, no change in temperature, no gas evolved, no precipitate, thus, no evidence of ions interacting and changing partners.
A powder of calcium carbonate can be taken and added with hydrochloric acid. This leads to the evolving of gas bubbles. These gas bubbles can be tested by either by passing it through lime water which will give a white precipitate. Or a lighter splinter can be introduced into the test tube. This splinter will go off immediately because of the carbon dioxide