Classifying Solids Using Physical Properties
Scientists classify matter according to physical and
chemical properties. To do so, they conduct many
qualitative analysis tests on different substances and
then group the substances into categories based on
properties. In this investigation, you will explore and
identify the physical properties of two different
classes of solids: ionic and molecular. Then you will
use the established criteria to classify an unidentified
solid provided by your teacher.
The physical properties that you will explore are
conductivity (ability to conduct electricity), hardness
(resistance to being scratched), melting point, and
solubility (ability to dissolve in water).
Purpose:
To determine how ionic and molecular solids
compare on the basis of conductivity, solubility,
hardness, and melting point?
Hypothesis:
From its chemical formula, predict whether each
solid (potassium iodide, sodium chloride, ammonium
chloride, benzoic acid, sucrose, camphor) is ionic or
molecular. Explain your Prediction.
Materials:
potassium iodide, KI(s)
sodium chloride, NaCl(s)
sucrose, C12H22O11(s)
camphor, C10H16O(s)
low-voltage conductivity apparatus
2 test tubes
test-tube rack
distilled water
scoopula
stirring rod
10-mL graduated cylinder
4 watch glasses
unidentified solid samples X and Y
microtray
Procedure:
Place a small amount of each chemical into a
numbered well in the microtray. Perform parts 1-5 of
the experiment as a comparison between an ionic
compound and a molecular one; KI and C12H22O11,
NaCl and C10H16O, Unknown X and Y.
Part 1: Testing for Solubility
1. Place the test tubes in the test-tube rack.
2. Using the masking tape, label the test
tubes sample one and two.
3. Pour 10 mL of distilled water into each test tube.
4. Add a small amount (fill the tip of the scoopula)
of each solid to its respective test tube.
5. Using a stirring rod, stir the mixtures. Observe
how completely each solid dissolves. Record your
observations in a table.
6. Keep the solutions for Part 2 of the investigation.
Part 2: Testing for Conductivity
7. Fill a beaker with 10 mL of distilled water.
Test for conductivity using the low-voltage
conductivity apparatus.
8. Place each solution from Part 1 into a beaker. Test
the conductivity of each solution. Record your
observations in your table.
9. Follow your teacher’s instructions for disposing
of the solutions.
Part 3: Testing for Hardness
10. Using the scoopula, place a few small crystals of
each solid on individual watch glasses.
11. Using the scoopula, attempt to crush a few of the
small crystals between the scoopula and the
watch glass.
12. Rank the relative hardness of each sample.
Record your rankings in your table.
Part 4: Melting Point
This is a comparison to see which substance melts
first.
13. Place a small sample each sample into separate
test tubes. Hold both samples in the Bunsen
burner flame until one of them melts. Record the
melting points as low or high.
Part 5: Classifying an Unidentified Sample
14. Obtain unidentified sample Xand Y from your
teacher. Test the sample for solubility in water,
conductivity, and hardness, melting point as
you did in steps 1 to 13. Record your
observations in your table.
Conclusion:
Answer the purpose.
Discussion/Analysis:
1. Use your observations to group the first six
solids into two categories.
2. Briefly summarize the physical properties of each
category.
3. Based on your summary of the physical
properties of the two categories, decide to which
category your unidentified sample belongs. Give
detailed reasons for your choice, using the
different properties of matter that you
investigated.
4. Are the physical properties that you studied in
this investigation sufficient for classifying the
solids into two categories? What other physical
properties could you investigate?
5. Evaluate your Prediction based on your Analysis.
Inv
Errors:
Suggest possible sources of error in the
Procedure, and explain their effects on your
results. How could you modify the Procedure to
reduce these sources of error?