How to grow a large crystal of copper (II) sulphate in 5 days

Presenting a faster way to grow large copper sulphate crystals! The pictured 4cm crystal took me 5 days by cooling, instead of the 3-6 weeks it would take by evaporation. [4 minute read]

Introduction

Growing copper (II) sulphate crystals was a childhood hobby of mine that I tried again as an adult. The usual way to grow crystals is slowly by evaporating a saturated solution, but I worked that you can grow them faster by occasionally adding supersaturated solution to the crystal mixture instead of waiting for water to evaporate. The accelerated growth does make the crystal more cloudy, and requires some some daily effort to create the solution.

Materials

1. 2 small glass beakers or empty jars
2. Distilled water
3. 50g copper sulphate
4. 0.2mm nylon fish line
5. Small plastic funnel
6. Glass ash tray
7. Plastic spoon
8. Toothpick or cardboard
9. Blu Tack
10. Cloth to cover jars

Most pharmacies should still have distilled water. For the copper sulphate you might call ahead, most pharmacies no longer stock it as an anti-fungal treatment.

Warning

Copper sulphate is moderately toxic when consumed. At least it tastes horrible. The solution stains absolutely everything porous. It even precipitates a copper coating onto steel spoons, hence the plastic spoon. Copper sulphate stains can be removed from cotton with peroxy-type stain removers. It and take weeks to come out from under your fingernails, so I recommend wearing gloves. On the plus side, copper sulphate is a traditional anti-fungal treatment for skin which is why pharmacies stock it.

Instructions

Make a supersaturated solution

1. Heat about 100ml of distilled water in a beaker in the microwave at medium power, watching to avoid boiling it.
2. Add about 25g of copper sulphate for starters
3. Stir with plastic spoon until no more is dissolves, taking about 2 minutes, thus saturating the solution.
4. Pour just the liquid solution into a second jar using a filter if you like.
5. Leave the solution to cool down to supersaturate it, which goes faster placing the beaker in freezer or ice water.

Grow and placing a seed crystal

1. Fill the glass ashtray about 5mm deep with supersaturated solution.
2. Place the ashtray in the fridge for a few hours..
3. Pick out either a single crystal or multicrystal with tweezers.
4. Tie a nylon fishing line around the crystal using a slip knot.
5. Suspend the crystal in a jar of cool supersaturated solution using toothpick and blu tack, taking care that it does not touch the sides.
6. Cover the jar with cloth to avoid dust getting in.
7. Place the jar in the fridge.

Now over the next 8 hours or so the extra copper sulphate will precipitate out either onto the growing crystal or to the bottom of the beaker, leaving behind a saturated solution.

Grow the crystal

Spend 10 minutes of your time morning and evening to refresh the saturated solution.

1. Remove the growing crystal and place to one side.
2. Pour about 75% of the saturated solution into a clean beaker #2.
3. With the 25% remaining solution in beaker #1, re-dissolve the crystals on the bottom by microwaving on low power then stirring.
4. Place beaker #1 containing not-quite-saturated hot solution in the freezer or ice water to cool it down, making it supersaturated.
5. Add the supersaturated solution to beaker #2, using a filter if necessary.
6. Suspend the growing crystal in beaker #2, place in fridge, and wait 8-12 hours.

If there is no crystal mat on the bottom, add more copper sulphate to the 25% being heated.

Tips

• Thin vs thick line: using 0.2mm nylon line prevents new crystals forming on the line. You can use a thicker line to grow a multi-crystal along the line directly without a seed crystal.
• Solubility increases with temperature: careful not to add hot solution to the crystal beaker, as it may not be supersaturated and could dissolve your crystal. Wait for it to cool first.
• Paint with clear nail polish: because CuS04.5H2O is a hydrated crystal, that dehydrates after a while to white powder (copper sulphate anhydrate). Painting helps reduce evaporation. Storing crystal on some copper sulphate powder can also help.

The SPCC National Crystal Growing Competition has advice for advanced crystal growing.