Download Lab Activity: Growing Crystals from Copper Sulfate

Lab Activity: Growing Crystals from Copper Sulfate
Background Information: According to your text, “crystal form is the visible expression
of a mineral’s internal arrangement of atoms,” (Tarbuck 2006, p. 51). As a mineral grows
or forms, the atoms that make up that mineral arrange themselves in a certain pattern. If
a mineral is given much time and space to form, a crystal with well-identified sides, top,
and bottom (called faces) will form. However, most of the time, minerals grow in
cramped spaces which result in crystal shapes that are difficult to identify because of
their intergrown mass of smaller crystals.
Safety Concerns: In order to understand how crystals form, we will
grow crystals in the lab using a chemical called copper sulfate. Copper
sulfate is used as a fungicide, herbicide, and pesticide. It is not to be
ingested and is a skin irritant. Safety glasses and gloves should be
worn throughout this lab to protect your eyes and skin. Wash your
hands immediately after working in the lab. Any horseplay will result in
immediate removal from the lab and you will receive no credit for doing
this activity until you come in and make up the lab on your own time.
Materials:
1 vial of copper sulfate crystals
6 inch piece of thread
baby food jar
beaker for heating water
1 seed crystal
wood stick
thermometer
distilled water
stirring rod or spoon
safety goggles
hot plate
hot pads
plastic gloves
Procedure
1. Heat 100 ml of distilled water to the temperature of 80 C
2. Add the copper sulfate to the water a little at a time stirring the solution
constantly
3. Once a few of the crystals fail to dissolve, you have added enough copper
sulfate
4. Pour the solution into the baby food jar and label it
5. Find a seed crystal with perfect edges (no chips or cracks in the small
seed crystal) and tie one end of the thread around the wood stick and the
other end around the seed crystal.
6. Make sure that the crystal does not touch the bottom of the jar by
wrapping excess thread around the wood stick.
7. Wait one week for the crystal to develop.
Analysis Questions:
1. Describe your crystal—how many sides or faces does it have? What
general shape does it resemble?
2. Using the rocks and minerals handbook or the overhead transparency as
a reference, decide what crystal form the copper sulfate best resembles.
What other minerals have this crystal shape?
3. What is a supersaturated solution? Describe how you made a
supersaturated solution.
4. What factors allowed the crystal to form? What factors interfered with the
crystal growth?
5. What was the purpose of the seed crystal?
6. Read the major processes by which minerals form on page 46 of your text.
Which of those four processes do you think we simulated in the lab?
Explain your answer. Think of a situation in the Earth where this might
occur.