NaC2H3O2 Lab (Castle Building Lab)
Answer the Pre-lab questions on separate sheet of paper. Use complete sentences when
applicable. This can be word-processed. To complete the pre-lab questions use the links
provided on the chapter webpage and reference the textbook.
Pre-lab Questions:
1. Name the salt NaC2H3O2
2. What is a solution? Define solvent and solute. What is the universal solvent?
3. Define an unsaturated, saturated, and supersaturated solution. Give an example of
each.
4. List three ways to increase the solubility of a salt.
5. List the colligative properties that change when the concentration of a solution
changes. Based on your life experience give several examples where you have used the
addition of a solute to change the colligative properties of a solution.
6. List and explain the steps for the formation of the ionic compound sodium chloride.
Sodium metal reacts with chlorine gas to form sodium chloride. (see web-link: step by
step process by which ionic compounds form).
7. Explain and provide examples for nucleation.
8. What variables affect crystal growth?
Purpose:
The purpose of this lab is to make a supersaturated sodium acetate solution and
successfully crystallize the solution while building a castle. Determine if crystallization
is an endothermic or exothermic reaction.
Hypothesis: A hypothesis is written as an “if… then…” statement testable through
experimentation. Come up with a hypothesis that is applicable to this experiment. After
completing the experiment. Come up with a new hypothesis that could be tested by
further experimentation.
Materials
3mL of deionized water
15g sodium acetate
watch-glass
disposable pipette
small beaker (100mL)
stirring rod
Bunsen Burner and ring stand
safety goggles
Safety procedures: safety goggles required, safety gloves preferred, Bunsen burner safety
(hair, sleeves)
This experiment runs a high risk of crystallizing before intended. Therefore, all
equipment must be clean and take precautions to not expose the super saturated solution
to any contaminants.
How it works:
Sodium acetate can dissolve in water in great quantities at high temperature, and if you
let the solution cool carefully to around room temperature, you have a clear
supersaturated solution. Disturbing this unstable equilibrium by dropping a small crystal
of sodium acetate into the solution makes the whole thing solidify; the sodium acetate
crystals growing radially outwards from the impact point of the seeding crystal.
Methods
1. Measure out 15g of sodium acetate into a 100mL clean beaker or flask.
2. Measure out 3mL of deionized water using a pipette or small graduated cylinder.
3. Adjust the height of your Bunsen burner so the flame is not directly under the
glass. Gently heat 15g of sodium acetate in 1mL of distilled water. Use heat to
increase solubility. As the solute is dissolving you can add another mL of water to
rinse down the inside of the beaker. Continue to gently heat. Use the last mL of
deionized water to rinse down the inside of the beaker for the last time. When you
have a clear solution turn off the heat. Make sure there are not solutes present!
4. Let the beaker cool in place. When cool you may proceed to step 5.
This is a competition! Whoever builds the tallest castle wins!
5. Place a crystal of sodium acetate onto a watch-glass. (*Put a pasco temperature
probe on the watch glass, hit play) *optional
6. Get a new pipette and rinse the end of the pipette with deionized water (to prevent
contamination). Fill the pipette with the supersaturated sodium acetate solution
(pipette must be clean or else it will activate crystallization prematurely) Using
the pipette, build a sodium acetate crystal castle, by dropping the super saturated
sodium acetate solution onto the sodium acetate crystal on the watch glass. Do not
touch the tip of the pipette to the castle. To form “castles” build the crystals on
top of one another. Continue building the castle until all the solution is gone or the
castle tips over. Take a picture of the castle. Measure the height of the castle.
Post lab ?’s:
1. Height of your castle in cm.
2. What happened when the supersaturated sodium acetate solution hit the watch
glass? Why was a sodium acetate crystal needed to activate the crystallization?
3. Did the watch glass feel warm or cold after crystallization?
*If you measured the temperature with the pasco probe then record lowest and
highest temperature.
4. IF the supersaturated solution crystallized prematurely then explain why it
happened and what you could of done to prevent premature crystallization. What
initiated the crystallization? Explain
5. On the atomic level: describe the particles of the supersaturated solution, describe
what is happening to the particles as the solution cools, and describe what
happens to the particles as it crystallizes. Compare the energy of the hot and cool
supersatured solution to the crystalline structure.
6. Describe the entropy of the super saturated solution and solid crystalline structure
7. Explain a supersaturated solution and how to make it. Provide examples of
supersaturated solutions (real world applications) and their purpose (Research).
8. Watch the Video Crystallization of supercooled water and explain how it relates
to the lab.
9. Mexico's cave of crystals. Research and explain the importance of Mexico's cave
of crystals either by viewing the video(The video is long but interesting) or use
resource(s) of your choosing. Cite your source. See CH7 opener.
10. Further knowledge leads to more questions. What questions came about
throughout this process? If you are not questioning then you are not practicing
science. Using this experiment as a starting point what would you do next to
further study crystallization?