In this video, we will focus on making insoluble salts.
When we prepare any salt, the first thing we need to consider is whether it is soluble in water. If the salt we want to make is an insoluble salt, we can form it by mixing two soluble salts together.
This method for preparing insoluble salt is called precipitation method.
Let’s consider making the insoluble salt, lead(II) sulfate.
We will need to use 2 soluble salts, one of it contains lead(II) cation, another contains sulfate anion.
Now, based on the solubility rules, we know that all nitrate salts are soluble. Hence, we can safely pair lead(II) cation with nitrate. The first salt solution is lead(II) nitrate, Pb(NO3)2.
Also, we know that all Group(I) salts are soluble. Hence, we can choose any Group I cation with sulfate. Let’s choose sodium ion, Na+. The second salt solution is sodium sulfate, Na2SO4.
When we mix these 2 solutions together, lead(II) ion will be attracted to sulfate ion. Insoluble lead(II) sulfate will be precipitated. Note, precipitate is a solid, hence we change the state symbol to s. Sodium ion and nitrate ion remains in the solution. Hence, the state symbol remains as aq.
Let’s consider another example. We make silver chloride.
Again, we need 2 soluble salts, one contains silver cation, Ag+ another contains chloride anion Cl–.
All nitrate salts are soluble, hence we can pair silver cation with nitrate. The first salt solution will be silver nitrate, AgNO3.
For the second salt, we can choose another Group I cation with chloride. Let’s choose potassium ion, K+. The second salt solution is potassium chloride, KCl.
Mix them together, silver ion will be attracted to chloride ion, insoluble silver chloride will be precipitated. Note, precipitate is a solid, hence we change the state symbol to s. Potassium ion and nitrate ion remains in the solution. Hence, the state symbol remains as aq.
Check out the question below.
Take some time to decide what are the possible starting reagents to make the insoluble salts.
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