The video below shows how you would use the reaction we have been talking about to make a pure sample of lead(II) iodide. Using precipitation reactions to make insoluble salts Solid lead(II) iodide is formed as a bright yellow precipitate.Ī precipitate is simply a solid formed by the reaction between two liquids or between a gas and a liquid. The attractions between lead(II) ions and iodide ions are strong enough to overcome attractions between the various ions and water molecules, and they stick together.

The only difference is what happens when a lead(II) ion meets iodide ions. If you mix this solution with potassium iodide solution, the ions in the mixture are now We will replace magnesium nitrate solution by lead(II) nitrate solution. Now let's make a slight change to what we have just described. The only time you are likely to come across them is in this topic. Note: You won't find iodides listed in the table of salt solubilities on the page mentioned above. What you end up with is simply a solution containing all four ions. The attractions between magnesium ions and iodide ions aren't strong enough for them to overcome the attractions between the ions and the water molecules. What happens if a magnesium ion meets an iodide ion?Īgain nothing happens. The attractions between potassium ions and nitrate ions aren't strong enough to overcome the attractions between the ions and the water molecules. What happens if a potassium ion meets a nitrate ion? If two positive ions meet, they will repel each other - so nothing happens. What happens when the various ions bump into each other? There are also lots of water molecules in both solutions.

There will, of course, be two nitrate ions for every one magnesium ion in the second solution to balance the charges. Mg(NO 3) 2 solution containing Mg 2+(aq) and NO 3 -(aq) ions. KI solution containing K +(aq) and I -(aq) ions, Imagine that you have two solutions which contain soluble salts: You may need to refer to the table of solubility on the page about salts and solubility. This page looks at the preparation of insoluble salts using precipitation reactions.

Formulation of a precipitate definition