Lab Title:
ARRANGEMENT OF ATOMS IN SOLID COMPOUNDS
CUBIC
HEXAGONAL ORTHORHOMBIC
Participants Names:
TRICLINIC
Andrew Gallagher
MONOCLINIC TETRAGONAL
Date: 9/28/11
Theory
Most solids are made of crystals. A crystal is a regular, repeating arrangement of atoms. The
simplest crystal conceptually is the simple cubic structure, where the atoms lie on a grid: layers of
rows and columns. When you look at a pure crystal you are seeing how the atoms are arranged at
the molecular level. Because this pattern keeps repeating itself it becomes large enough for you to
“see” the arrangement of the atoms. Scientists grow crystals of various compounds so that they
can see how the atoms are arranged. One method of growing crystals is called recrystallization.
This is a process that is used to purify solid material by dissolving the solid (called a solute) in an
appropriate liquid (called a solvent) and then having the material come out of a saturated solution
in crystalline form. As the solvent evaporates the solid crystals begin to grow larger. Depending
upon conditions, one may obtain a mass of many small crystals or one large crystal.
Objectives
 Observe the arrangement of atoms in 4 compounds: Alum (AlKSO4), Borax (Sodium
Borate (Na2B4O7)), Copper Sulfate (CuSO4) and Table Salt (Sodium Chloride (NaCl)) by
identifying the crystal shape that grows after completion of the recrystallization process.
Procedure
1.
Using a 10 ml graduated cylinder place 15 ml of water into each of the clean 30 ml
beakers.
2.
Place beakers “A” and “B” on the hot plate and turn to “5.”
DO NOT LET THE WATER BOIL. TURN IT DOWN IF NECESSARY.
3.
Use a weighing paper to measure 1.8 grams of Alum and a new paper to measure
1.8 grams of Borax.
USE A NEW PAPER FOR EACH SUBSTANCE YOU MEASURE! THROW OUT
THE PAPER AFTER YOU ARE FINISHED.
4.
Place the Alum in beaker “A” and the Borax in beaker “B.”
5.
Use the correct stirring stick to stir each substance until it is completely dissolved.
6.
Pour the saturated solution that you have made into the Petri dish that matches the
label on the beaker.
7.
Wash and dry the beakers and the stirring sticks and put away.
8.
Repeat this process for Copper Sulfate (1.8 grams) and Salt (2.0 grams).
9. Turn off the hot plate when you are finished and clean up your area. Throw all trash
away.
10. DO NOT DISTURB THE PETRI DISHES FOR THE NEXT FEW DAYS!
Data
Compounds:
ALUM
BORAX
COPPER SULFATE
TABLE SALT
Formula
Formula
Formula
Formula
AlKSO4
Na2B4O7
CuSO4
NaCl
Chemical Name
Chemical Name
Chemical Name
Chemical Name
Aluminum Potassium Sulfate
Sodium Borate Copper Sulfate
Sodium Chloride
Elements
Elements
Elements
Elements
Aluminum
Potassium
Sulfur
Oxygen
Sodium
Boron
Oxygen
Copper
Sulfur
Oxygen
Sodium
Chlorine
CRYSTAL TYPE
CRYSTAL TYPE
CRYSTAL TYPE
CRYSTAL TYPE
_________________
_________________
_________________
________________
Observations
1. What is a crystal?
Answer: A regular, repeating pattern of atoms
2. What does a crystal tell you about the atoms in a solid compound?
Answer: Arrangement of atoms.
3. Name and describe the process used to grow crystals in this lab.
Answer: 10mL of water in each graduated cylinder, with 1.8 grams of copper sulfate,
borax, and alum, and 2.0 grams of table; one in each cylinder. Pour the solution into a
Petri dish, and check after a few days.
4. What is the solute and solvent in this lab?
Answer: The solute is water, and the solvents are borax, alum, copper sulfate, and table
salt
5. What is a saturated solution?
Answer: The maximum amount of solute is dissolved into the solvent. Any more of the
solute would result in sediment or particles undisolved in the solvent.
6. What is a compound?
Answer: Two or more elements chemically combined.
Conclusion
(labeled sketches of individual crystals of each compound)
1. Why did you need to be careful about throwing away weighing papers or not using the
same stirring stick for different solutions? What would happen if you had not followed
these directions?
Answer:
2. Why did we pour the solution into a petri dish instead of leaving it in the beaker?
Answer:
3. Were there any problems with the way the crystals grew? If so hypothesize about what
may have caused the problem.
Answer:
4. Which compound was the most difficult to determine the crystal shape. Explain.
Answer:
First objective:
After observing the arrangement of atoms in 4 compounds, Alum (AlKSO4), Borax (Sodium
Borate (Na2B4O7)), Copper Sulfate (CuSO4) and Table Salt (Sodium Chloride (NaCl)) the crystal
shape that grows after completion of the recrystallization process was identified.
The crystal shapes of the 4 compounds were
Error Analysis