Electrolytes and nonelectrolytes lab report

Logger Pro 13 Properties of Solutions: Electrolytes and Non-Electrolytes In this experiment, you will discover some properties of strong electrolytes, weak electrolytes, and non-electrolytes by observing the behavior of these substances in aqueous solutions. You will determine these properties using a Conductivity Probe. When the probe is placed in a solution that contains ions, and thus has the ability to conduct electricity, an electrical circuit is completed across the electrodes that are located on either side of the hole near the bottom of the probe body (see Figure 1). This results in a conductivity value that can be read by data-collection software. The unit of conductivity used in this experiment is the microsiemens per centimeter, or µS/cm. Figure 1 The size of the conductivity value depends on the ability of the aqueous solution to conduct electricity. Strong electrolytes produce large numbers of ions, which results in high conductivity values. Weak electrolytes result in low conductivity, and non-electrolytes should result in no conductivity. In this experiment, you will observe several factors that determine whether or not a solution conducts, and if so, the relative magnitude of the conductivity. Thus, this simple experiment allows you to learn a great deal about different compounds and their resulting solutions. In each part of the experiment, you will observe a different property of electrolytes. Keep in mind that you will be encountering three types of compounds and aqueous solutions: Ionic Compounds These are usually strong electrolytes and can be expected to 100% dissociate in aqueous solution. Example: NaNO3(s) → Na+(aq) + NO3–(aq) Chemistry with Vernier © Vernier Software & Technology 13 - 1 Experiment 13 Molecular Compounds These are usually non-electrolytes. They do not dissociate to form ions. Resulting solutions do not conduct electricity. Example: CH3OH(l) → CH3OH(aq) Molecular Acids These are molecules that can partially or wholly dissociate, depending on their strength. Example (strong electrolyte): H2SO4 → H+(aq) + HSO4–(aq) (100% dissociation) Example (weak electrolyte): HF ↔ H+(aq) + F–(aq) (<100% dissociation) OBJECTIVES l l l l Write equations for the dissociation of compounds in water. Use a Conductivity Probe to measure the conductivity of solutions. Determine which molecules or ions are responsible for conductivity of solutions. Investigate the conductivity of solutions resulting from compounds that dissociate to produce different numbers of ions. MATERIALS computer Vernier computer interface Logger Pro Conductivity Probe Stir Station and magnetic stir bar Electrode Support 250 mL beaker wash bottle and distilled water tissues H2O (tap) H2O (distilled) 0.05 M NaCl 0.05 M CaCl2 0.05 M AlCl3 0.05 M HC2H3O2 0.05 M H3PO4 0.05 M H3BO3 0.05 M HCl 0.05 M CH3OH (methanol) 13 - 2 Chemistry with Vernier Properties of Solutions: Electrolytes and Non-Electrolytes PROCEDURE 1. Obtain and wear goggles! Caution: Handle the solutions in this experiment with care. Do not allow them to contact your skin. Notify your teacher in the event of an accident. 2. The Conductivity Probe is already attached to the interface. It should be set on the 0–20000 µS/cm position. 3. Prepare the computer to monitor conductivity by opening the file “13 Electrolytes” from the Chemistry with Vernier folder of Logger Pro. 4. Obtain the Group A solution containers. The solutions are: 0.05 M NaCl, 0.05 M CaCl2, and 0.05 M AlCl3. 5. Measure the conductivity for each of the solutions. a. Carefully raise each vial and its contents up around the Conductivity Probe until the hole near the probe end is completely submerged. Important: Since the two electrodes are positioned on either side of the hole, this part of the probe must be completely submerged. b. Briefly swirl the beaker contents. When the reading has stabilized, record the value. c. Before testing the next solution, clean the electrodes by surrounding them with a 250 mL beaker and rinsing them with distilled water. Blot the outside of the probe end dry using a tissue. It is not necessary to dry the inside of the hole near the end of the probe. 6. Obtain the four Group B solution containers. These include 0.05 M H3PO4, 0.05 M HC2H3O2, 0.05 M H3BO3, and 0.05 M HCl. Repeat the Step 5 procedure. 7. Obtain the five Group C solutions or liquids. These include 0.05 M CH3OH, 0.05 M C2H6O2, distilled H2O, and tap H2O. Repeat the Step 5 procedure. Chemistry with Vernier 13 - 3 Experiment 13 DATA TABLE Solution Conductivity (µS/cm) A - CaCl2 A - AlCl3 A - NaCl B - HC2H3O2 B - HCl B - H3PO4 B - H3BO3 C - H2Odistilled C - H2Otap C - CH3OH PROCESSING THE DATA 1. Based on your conductivity values, do the Group A compounds appear to be molecular, ionic, or molecular acids? Would you expect them to partially dissociate, completely dissociate, or not dissociate at all? 2. Why do the Group A compounds, each with the same concentration (0.05 M), have such large differences in conductivity values? Hint: Write an equation for the dissociation of each.