Growing a chemical “reef”

How to grow a chemical “reef” using diffusion

Safe­ty pre­cau­tions

Wear pro­tec­tive gloves, glass­es, and a mask.

Reagents and equip­ment

  • glass con­tain­er;
  • 100 mL dis­tilled wa­ter;
  • 2 g cop­per(II) sul­fate;
  • 2 g potas­si­um hex­a­cyano­fer­rate(II);
  • 2 g am­mo­ni­um iron(III) sul­fate.

Step-by-step in­struc­tions

Pour 100 mL warm dis­tilled wa­ter into the glass con­tain­er. Add, in or­der, 2 g cop­per(II) sul­fate, 2 g potas­si­um hex­a­cyano­fer­rate(II), and 2 g am­mo­ni­um iron(III) sul­fate. Af­ter some time, col­or­ful pre­cip­i­tates re­sem­bling reefs will form.

Process de­scrip­tion

In wa­ter, cop­per(II) sul­fate, potas­si­um hex­a­cyano­fer­rate(II), and am­mo­ni­um iron(III) sul­fate dis­solve and dis­so­ci­ate into ions. These ions aren’t sta­tion­ary – they grad­u­al­ly spread out through­out the en­tire so­lu­tion. This is an ex­am­ple of a phe­nom­e­non known as dif­fu­sion. The ions even­tu­al­ly en­counter one an­oth­er and form col­or­ful, in­sol­u­ble com­pounds that re­sem­ble real reefs! When hex­a­cyano­fer­rate(II) ions and cop­per(II) ions “meet” in the so­lu­tion, they form a red­dish-brown com­pound of cop­per(II) hex­a­cyano­fer­rate(II):

2Cu­SO₄ + K₄[Fe(CN)₆] = Cu₂[Fe(CN)₆]↓ + 2K₂­SO₄

Mean­while, hex­a­cyano­fer­rate(II) ions and iron(III) ions form a blue pre­cip­i­tate of iron(III) potas­si­um hex­a­cyano­fer­rate(II):

2K₄[Fe(CN)₆] + 2N­H₄Fe(SO₄)₂ = 2KFe[Fe(CN)₆]↓ + (NH₄)₂SO₄ + 3K₂­SO₄