Names:____________________________________________________________________________Date:___________________ Per:__________________ COMPARING IONIC and COVALENT COMPOUNDSPurpose: • To compare physical properties of ionic and covalent compounds • To determine whether an unknown substance is ionic or covalent • To build a conductivity tester • Identify conductors and insulatorsBackground:Why does electricity only flow through the copper on a circuit board? Simple! Copper, like most metals, is aconductor of electricity. That means that electricity can easily flow through it, as opposed to an insulator whichis a material that electricity does not easily flow through, like rubber or plastic. And then there aresemiconductors, but we’ll save them for a different episode.So why does electricity flow easily through conductors? Well, that is a little more complicated to explain.Basically, think of electricity as energy that flows through electrons. [Reminder: electrons are the tiny,negatively charged subatomic particles that orbit around the nucleus of the atom.] Some of the outermostelectrons of metal atoms aren’t strongly attracted to the nucleus. This creates a sort of “cloud” of electrons thateasily move around, thereby easily allowing them to transfer energy.In order for electricity to flow through a circuit, the circuit must be a complete loop – from the battery, to adevice, then back to the battery, through a conducive material. This is called a “closed circuit.” The two openalligator clips act as a type of switch, controlling when the circuit is open or closed. When a conductive materialis placed between the two clips, the circuit is complete and electricity can flow.By the way, it is important to connect the buzzer as I described above. It is like a one-way street – electricitycan only flow one direction through it. Connect it the other way and it won’t work! There are several deviceslike this, just like there are some that can electricity flow through either direction (like a light bulb).Pre-lab Questions:1) Based on what you’ve learned about electronegativity differences and bond types, predict which group ofelements (A-C), (D-F) or (G, H) are ionic and which are covalent and which are metallic. Explain yourreasoning for each choice2) Outline the procedure.Materials: SOLIDS LIQUIDSLab burner sodium chloride (A) Isopropyl alcohol (I)Conductivity apparatus potassium iodide (B) Vinegar (5% acetic acid) (J)Scoopula or spoons baking soda (C) De-ionized water (K)Deflagrating spoon/aluminum foil sugar (D) Tap water (L)Watch glass/paper camphor (E)Beaker /cups Aspirin (F) OTHER Paper clip (G) Unknown solid Aluminum strips (H)Safety precautions:Safety goggles must be worn. Use caution when heating compounds. Follow instructions for the conductivitymeter.
Names:____________________________________________________________________________Date:___________________ Per:__________________PROCEDURE: 1) Complete a chart for your observations. And GIVE IT A TITLE. 2) Collect a small pea size sample of each compound Observations/Physical Properties 3) Try to detect if any substances have an odor by using the wafting method. 4) Determine whether each substance seems hard or soft. Do this by rubbing a small sample of each between your fingers. Try to crush a few crystals of each. Place each compound in the watch glass at a time and use a scoopula to crush them. Melting Point 5) Light the burner. Place a small sample of substance A into a deflagrating spoon and a small sample of substance D into the other. Record the one that melts first as low and the other as high. You do not need to melt the higher one. Repeat with substances B and E, C and F. 6) Repeat step 5 with your unknown. Conductivity 7) Make a solution of each solid compound using distilled water in separate beakers. (Use the same solid samples and add ______mL of DI water). 8) Test the conductivity of each solution, including your unknown. Let’s build a conductivity tester so you can test substances to see how conductive they are! What You Need: 3 alligator clip wires An LED light bulb 60mA or a 12VDC buzzer a 9V battery What to Do: 1. Connect one wire to the negative (-) terminal of the battery. 2. Connect the other end of the wire to a wire on the LED (the black wire on the buzzer), making sure the metal on the clip is grabbing the exposed metal of the wire. 3. Connect a second wire to the positive (+) terminal of the battery 4. Connect a third wire to the other wire on the LED (or the red wire on the buzzer), making sure the metal on the clip is grabbing the exposed metal of the wire. 5. To test the circuit, touch the two empty alligator clips together. What happens?? (note as observations). 6. Place a material between the two clips to test them. Or, you can immerse the two ends into liquids to see how conductive liquids are. 7. In the space below, draw a picture of the conductivity tester you created. Figure 1 creating a closed circuit
Names:____________________________________________________________________________Date:___________________ Per:__________________TITLE:___________________________________________________________________________________Substance Type of Observations Melting Conductivity bond Point (High or (yes or no) Low) As a solid? In solution?A. Sodium Chloride NaClB. Potassium Iodide KIC. Baking soda NaHCO3D. Sugar C12H22O11E. Camphor C10H16OF. Acetylsalicylic acid (Aspirin) C9H8O4G. Paper clipH. Aluminum stripsI. Isopropyl alcohol N/A C3H8OJ. Vinegar N/A CH3COOHK. De-ionized water N/A H2OL. Tap water N/A H2OM. UnknownPost-Lab Questions: 1. Compare the physical properties of ionic and covalent substances. 2. What is the number of your unknown? Is it ionic or covalent? How do you know? 3. Intermolecular forces exist between molecules or ions. Based on this lab, which do you think are stronger, intermolecular forces between covalent compounds or intermolecular forces between ions? 4. Which type of substance conducted electricity when dissolved in water? What is the difference between ionic and covalent substances that causes this? 5. List the solids that were good conductors of electricity. 6. List the liquids that were good conductors of electricity. 7. Which solutions are electrolytes? List them in order from strong to weak. 8. Which liquids were nonconductors of electricity? 9. Why is de-ionized water not an electrolyte? What must be done to de-ionized water to conduct electricity? 10. Based on what you know about electrical conduction explain why some of the substances did not conduct electricity. 11. Compare the conductivity of solid NaCl and the solution of NaCl. Explain the difference. 12. Which type(s) of bonds resulted in electrical conduction and which type(s) of bonds did not. Explain why ionic compounds (i.e., salts and bases) in the solid phase do not conduct an electric current, but in the liquid state and in aqueous solution, these same compounds act as electrolytes.