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Study Guide: Experiment: Growing Salt Crystals

This experiment includes the creation of a supersaturated solution in which the solution (liquid) contains more salt than water can usually hold.

Temperature: As the heated water cools, the solution becomes unstable, and the dissolved salt “grows” onto the string.

Evaporation: As the water evaporates, the salt stays behind, making the solution even more unstable, causing the crystal to grow further.

Safety

Adult supervision is required. Please see the safety warnings below.

Materials

• Required for Safety! A helpful adult
• 1 strong widemouth jar, such as a Mason jar
• $\frac{1}{2}$ cup (120 ml) of tap water or distilled water
• $\frac{1}{2}$ cup (120 ml) of salt.
• Note: Different salts produce different results:
  • Table salt crystals will take a few days to grow.
  • Iodized salt does not work well, but will form a few crystals.
  • Epsom salt grows faster than table salt, and will create smaller, needle-like crystals. (found in the Pharmacy.)
  • Alum salt grows quickly, sometimes making visible crystals within a few hours. (found in the spice section of grocery stores.)
• 1 small pan (for boiling the water)
• About 6 inches of string. The string should have tiny grooves and rough edges so that salt can latch onto it. A braided string is ideal. Do not use fishing line.
• 1 pencil or popsicle stick, long enough to lie across the top of the jar.
• 1 piece of styrofoam or a spare towel
• Optional:
  • A few drops of food coloring. Note: Too much food coloring prevents good crystal formation.
  • Tape (to hold the pencil in place)

Directions

1. Preparation

   1. Tie one end of the string around the pencil or popsicle stick.
   2. Dangle the string into the jar to measure the length. Cut the string short enough to avoid touching the bottom.
      • Note: The crystal will be lumpy or small if the string touches the bottom or sides of the jar.
   3. Place the wooden spoon in the jar. This will help ensure that the sudden heat from boiling water does not shatter the jar.

2. Create the Solution

   1. Safety Warning! Have an adult heat a pan of water until it just reaches the boiling point. As soon as the water reaches a bubbling boil, remove it from the heat and turn off the stove.
   2. Safety Warning! Have an adult slowly pour the hot water into the jar.
   3. Safety Warning! Have an adult slowly pour about $\frac{1}{4}$ to $\frac{1}{2}$ cup of salt into the jar, stirring constantly until the water is clear. If you don’t see any salt grains in the water, stir in another spoonful.
   4. Keep gradually stirring in more salt until you see a few salt grains that won’t dissolve. Stop adding salt as soon as you see such grains.
   5. Optional: Add a couple of drops of food coloring to change the color of the crystals.

3. Setup and Observation

   1. Balance the pencil on top of the jar, and hang the string into the water without letting it touch the bottom or sides. If needed, use the wooden spoon to push the string deeper into the water. If the pencil won’t stay still, tape it to the jar.
   2. Sometimes tying a small weight to the bottom end of the string can help. Be sure such a weight is clean and can not contaminate the solution.
   3. Place the Styrofoam, spare towel, or similar material in a cool, dark spot that will be undisturbed by vibrations (loud noises, refrigerators, pounding feet, etc.), and set the jar on top of it.
   4. Wait for it! Check back regularly. For best results, don’t touch or shake the jar. The crystals should keep growing for a week or more.

   More Information

   How To Make Beautiful Epsom Salt Crystals ( For Kids )

   Making Crystals with Epsom Salt