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National Chemistry Week - Experiments - Growing Crystals
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Objective:
To grow crystals from a supersaturated solution. A solid that dissolves in a liquid (solvent) is called a solute. Solute can be added to the solvent until no more will dissolve. At this point the solution is said to be saturated. Heating of a saturated solution will allow more solute to be dissolved. When no more solute dissolves in the heated solution the solution is said to be supersaturated. These solutions are unstable and the solute will want to crystallize out. As the solution cools more solute will crystallize. Each solute has a characteristic shape. For instance sodium chloride is cubic, magnesium sulphate is orthorhombic, and sodium bicarbonate is monoclinic.
Materials:
- 2 tall narrow jars
- tweezers
- kettle
- rubber band
- pencil
- spoon
- thread
- washer or paper clip (optional)
- coffee filter papers
- magnifying glass
- sugar, sodium chloride (salt), magnesium sulphate (Epsom salts), sodium bicarbonate (baking soda)
Procedure:
This experiment will take a few days to complete. If you are having difficulty forming crystals try tying a small washer or paper clip to the end of the string.
- Fill one jar with hot water and stir in one of the salts until no more salt will dissolve.
- Tie one end of the thread to the middle of a pencil and carefully hang it in the solution so it is not touching the bottom or the sides (secure the pencil so that it doesn't roll).
- When the solution has cooled and no more crystals have grown on the thread remove the thread and place it on a coffee filter (crystals may grow on the bottom of the jar instead of the thread). If no crystals form try supersaturating the solution again.
- Decant the liquid into a second jar being careful not to pour out any crystals (filtering may be necessary).
- Carefully scrape the crystals off the thread (or remove any off the bottom of the jar) and examine them using a magnifying glass (be careful during handling because the crystals will be soluble in water and perspiration can damage the surfaces).
- If large enough single crystals are formed tie one to some thread and hang it in the saved saturated solution.
- Watch the crystal and see if it grows over the following days.
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