If a substance dissolves well in a particular liquid, we say that it is soluble. if a substance does not dissolve at all in a particular liquid, we say that it is insoluble.
A salt is a substance that can be made by reacting an acid with an alkali.
Lead nitrate and potassium iodide are salts that are soluble in water. Their solutions react together to produce lead iodide and potassium nitrate. Lead iodide is insoluble in water. It appears as a yellow precipitate, made up of particles of lead iodide suspended in the liquid.
Here are the equations for reaction:
lead nitrate + potassium iodide -> lead iodide + potassium nitrate
Pb(NO3)2 (s) + 2Kl (aq) -> PbI2 (s) + 2KNO3 (aq)
Notice how the equation is correctly balanced using numbers in front of Kl and KNO3.
The state symbols show that all the substances are dissolved in water, apart from lead iodide, which is insoluble and so is present as a solid. You will need to know how to use state symbols like these in I/GCSE Chemistry.
A reaction in which an insoluble solid is produced from two soluble substances is called a precipitation reaction. It happens if the reactants are soluble and at least one of the products is insoluble but not if all the products are soluble.
Drafted by Catrina (Chemistry)