Name: _________________________________ Date: ___________________________
Lab: Identifying Compounds and Mixtures
Directions: Read through the review chart below and answer the pre-lab questions. Then,
rotate through the stations, identifying each substance as a compound or mixture. If it is a
mixture, be sure to include whether it is homogeneous or heterogeneous. Be sure to include 3
observations of the substance, and a meaningful REASON for your classification!
Element
• Made of ONE kind of
atom (found on the
periodic table)
• Cannot be separated into
any simpler form
chemically or physically
Compound
Made of TWO OR MORE kinds
of atoms chemically
combined in a certain
ratio
(e.g. water molecule
is 2 hydrogen and 1
oxygen atoms combined)
Mixture
• 2 or more elements or
compounds mixed together
PHYSICALLY.
• NOT CHEMICALLY
COMBINED!
• Each part keeps its own
chemical identity
• Can be heterogeneous
(different throughout) or
homogeneous. (the same
throughout)
Mixtures
Solutions are groups of molecules that are mixed and
evenly distributed in a system. Scientists say that
solutions are homogenous mixtures. Everything in a
solution is evenly spread out and thoroughly mixed.
Solutions look uniform, meaning you cannot see the
different parts of the mixture.
Heterogeneous mixtures have a little more of one thing
(higher concentration) in one part of the system when
compared to another, and you are able to see the different parts of the mixture.
Let's compare salt in water (H2O) to sand in water. Salt dissolves and is spread throughout the
glass of water. The sand sinks to the bottom. The salt-water is a homogenous mixture while the
sand-water is a heterogeneous mixture. Both are mixtures, but only the salt-water can also be
called a solution.
Pre-Lab Questions
1. What is the difference between an atom and a compound?
2. How is a heterogeneous mixture different from a homogeneous mixture?
3. How is the way a mixture is combined DIFFERENT from how a compound is combined?
4. What is easier to separate, a mixture or a compound? Why?
5. Which can be found on the periodic table: elements, compounds or mixtures?
Name: ____________________________ Date: _______________________
Part Number/
Identity of
Substance
Description/
Observations
1.
Alka Seltzer
and Water
Before you added the
tab:
After:
2.
Salt and
Water
Before you mixed
them:
After:
3.
Before you mixed
them:
Sand and
Water
After:
4.
Before you separated
them:
Trail Mix
After:
Classification:
(Formation of a Compound,
Homogenous Mixture, or
Heterogeneous Mixture)
Explain why you
classified it this way.
Part 1
Alka Seltzer is a medicine that is used for an upset stomach, and it is made from sodium
bicarbonate (NaHCO3). To make the medicine work, you have to add it to water to activate it.
Parts of the tablet will chemically combine with water, and CO2 gas is made.
o
o
o
o
o
Get a test tube with an Alka Seltzer tablet and a beaker from the front prep desk.
DO NOT TOUCH THE ALKA SELTZER TABLET!!!!!!!!
Fill the beaker with water to the 150mL line.
Add the tablet to the water. Notice what happens.
Complete the chart for Part 1.
Part 2
Salt (Na+Cl-) is a compound made from Sodium (Na) and Chlorine (Cl). Together, they form an
ionic bond. When you add it to water, the salt dissolves in the water. Dissolving is different
from melting. The temperature required to melt salt is 801°C (1,474°F)!!! Now that’s hot!
Water is a liquid at room temperature, which is about 20°C (70°F) which is much, much lower
than the melting point of salt.
o
o
o
o
Dump out the water from part 1 into the sink, rinse and refill the beaker with water.
Get salt and a stirrer from the front of the room on the prep desk.
Add the salt to the water and stir. Notice what happens.
Complete the chart for Part 2.
Part 3
Sand is made of a compound called silica (SiO2), and is unreactive in water, which means it will
not make a chemical reaction. Sand will not dissolve in water either.
o Dump the water from part 2 and refill the beaker with water.
o Get sand from the front prep desk.
o Add the sand to the beaker and stir. Complete the chart for Part 3.
Part 4
Trail mix is a tasty treat to take on a hike. The parts of trail mix remain the same when you add
them to a bag, and no chemical reaction occurs.
o Return the beaker to front desk, and exchange it for a bag of trail mix. DO NOT DUMP
OUT THE SAND INTO THE SINK!!!!!!!!!!!!!!!!!!!!!!
o Get a piece of blank paper.
o Dump the trail mix onto the paper.
o Separate the pieces of the trail mix into its parts, and complete the chart
o Clean up by eating the trail mix!
Post Lab Questions
1. What is another name for a solution? ______________________________________
2. Of the three mixtures, which one was considered a solution?
__________________________________________________________________
__________________________________________________________________
a. A solution is always made from something called a solute and a solvent. The solute
is what gets dissolved, and the solvent is what causes the solute to dissolve. In the
solution we looked at, what was the solute?______________________________
What was the solvent? ____________________________________________
3. You were able to separate the parts of the trail mix very easily. How could you separate
the water and sand?
__________________________________________________________________
__________________________________________________________________
__________________________________________________________________
How could you separate the water from the salt? (Hint: You won’t be able to use a filter)
__________________________________________________________________
__________________________________________________________________
__________________________________________________________________
4. What is generally easier to separate, a homogenous mixture or a heterogeneous mixture?
__________________________________________________________________
__________________________________________________________________