“Copper sulfate crystals” experiment

How to grow a beautiful blue crystal with a copper salt

We all like sto­ries about he­roes who go on end­less quests to find trea­sure. But some­times trea­sures can be found very near­by. In this ex­per­i­ment, we’ll show you how to grow a beau­ti­ful blue crys­tal, with­out trav­el­ing to the ends of the Earth.

Safe­ty pre­cau­tions

Wear pro­tec­tive gloves and glass­es.

Warn­ing! Only un­der adults su­per­vi­sion.

Reagents and equip­ment:

  • cop­per(II) sul­fate pen­tahy­drate (70 g);
  • hot wa­ter (100 ml);
  • beaker;
  • plas­tic twine;
  • fun­nel with cot­ton wool;
  • foil.

Step-by-step in­struc­tions

Sprin­kle cop­per(II) sul­fate pen­tahy­drate into a beaker and pour hot wa­ter over it. Stir thor­ough­ly for 10-15 min­utes. In this way, we make a sat­u­rat­ed so­lu­tion. Re­move the re­main­ing crys­tals and dust from the so­lu­tion us­ing the fun­nel with cot­ton wool. Cov­er the so­lu­tion with foil and leave in a dark place for 24 hours.

Then pour the so­lu­tion into an­oth­er beaker and take out the crys­tals that have formed. It’s im­por­tant to choose a crys­tal with the right form, with­out cracks and oth­er de­fects. Tie twine around the crys­tal and im­merse it in the so­lu­tion we made pre­vi­ous­ly, so that the crys­tal does not touch the walls of the beaker. Cov­er with foil and put in a dark place. Af­ter a month a large crys­tal will grow on the twine!

Pro­cess­es de­scrip­tion

In a sat­u­rat­ed so­lu­tion, the sub­stance is at max­i­mum con­cen­tra­tion and does not dis­solve fur­ther at the giv­en tem­per­a­ture. At room tem­per­a­ture (25 °С, 77 °F), the sol­u­bil­i­ty of cop­per(II) sul­fate pen­tahy­drate in wa­ter is around 35 g/100 g of wa­ter. When heat­ed to 90 °С (194 °F), sol­u­bil­i­ty in­crease to 100 g/100 g of wa­ter.

So when it cools the so­lu­tion be­comes sat­u­rat­ed, i.e. more of the sub­stance is dis­solved in it at the giv­en tem­per­a­ture. As a re­sult, the “sur­plus sub­stance”–cop­per(II) sul­fate pen­tahy­drate in our case – pre­cip­i­tates in the form of crys­tals, and the so­lu­tion once more be­comes sat­u­rat­ed. If you place a crys­tal in this so­lu­tion, it will not dis­solve, but be­come cov­ered with ions of the dis­solved salt.