In this video, we work out the chemical reactions to prepare pure copper(II) sulfate salt.
When we prepare any salt, the first thing we need to consider is whether it is soluble in water. The salt we are focusing on is copper(II) sulfate.
For sulfates, we know all are soluble except calcium sulfate, lead(II) sulfate and barium sulfate. Hence, copper(II) sulfate is a soluble salt in water.
There are 3 ways to form a salt that is soluble in water. Reaction of acid with 3 different substances – metal, carbonate or base. For easy memory, you can remember as my cute baby.
You realise we are making use of the reaction of acid to form the soluble salt. We know that acid reacts with reactive metals to form soluble salt and hydrogen gas, acid reacts with carbonates to form soluble salt, carbon dioxide gas and water, acid reacts with base to form soluble salt and water. Let’s check each of the possibilities out.
Acids react with reactive metals.
The keyword here is reactive. Do note, different metals react with acids at different rates. Some metals are very reactive and reaction with acids is very vigorous and fast, some metals are not so reactive, or even unreactive. Speaking of which, these few metals do not react with dilute sulfuric acid in the school Chemistry Lab – lead, copper, silver and gold. Hence, to form copper(II) sulfate in the lab, we can’t use this method because copper metal is unreactive with dilute sulfuric acid.
Acids react with metal carbonates.
What about the next reaction? Can we make use of the reaction of acid and carbonate to make copper(II) sulfate. Yes we can. To provide the sulfate ion, we will choose sulfuric acid, and the carbonate we use needs to contain the copper(II) ion. Hence, we will use copper(II) carbonate. When copper(II) carbonate reacts with sulfuric acid, copper(II) sulfate is formed, together with water and carbon dioxide gas. We can’t observe the production of water, but we will observe effervescence in this reaction due to production of carbon dioxide gas.
Acids react with bases.
What about reaction with oxide? Yes we can. Similarly, to provide the sulfate ion, we will choose sulfuric acid, and the oxide we will need to choose must contain copper(II) ion. Hence, we will use copper(II) oxide. When copper(II) oxide reacts with sulfuric acid, copper(II) sulfate is formed, together with water. In this reaction, no gas is formed. We will not observe any effervescence. Hence in order to ensure complete reaction, we will add insoluble copper(II) oxide in excess, and we can get rid of that by filtering away later. After forming copper(II) sulfate, we will be interested to obtain the solid salt from this solution. We will achieve that by crystallisation.
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