Properties of Solutions Electrolytes and Non-Electrolytes

1、NAME: _PRE-LAB QUESTIONS ELECTROLYTES1. What is meant by saying something is an electrolyte, weak electrolyte or non-electrolyte?2. If a substance is dissolved in water and it produces ions when it dissolves, it will be a(n) _. If it does not produce ions it will be a(n)_.3. What group of molecular

2、compounds typically will conduct?4. Which will not conduct? A. Distilled water B. Salt water C. Bath water5. Why will a block of salt used with cattle not conduct though it would if it was melted?Name:_Properties of Solutions: Electrolytes and Non-Electrolytes In this experiment, you will discover s

3、ome 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 co

4、nduct electricity, and electrical current is completed across the electrodes that are located on either side of the hole near the bottom of the probe unit (see Figure 1). This results in a conductivity value that can be read by the CBL System. The unit of conductivity used in this experiment is the

5、microsiemens, or µS. 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

6、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 magnitudes of the conductivity. Thus, this simple experiment allows you to learn a great deal about different compounds and their resulting solut

7、ions. Figure 1 In each part of the experiment, you will be observing 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 aqueou

8、s solution. Example: NaNO3(s) Na(aq) + NO3-(aq) Molecular Compounds These are usually non-electrolytes. They do not dissociate to form ions. Resulting solutions do not conduct electricity. Example: CH3CH2OH CH3CH2OH (aq) Molecular Acids These are molecules that can partially or wholly dissociate, de

9、pending on their strength. Example: Strong electrolyte H2S04 H+ (aq) + HS04- (aq) (100% dissociation) Example: Weak electrolyte HF H+ (aq) + F- (aq) (100% dissociation) MATERIALS CBL System Conductivity probe Wash bottle with distilled water Ring stand Utility clamp H2O (tap) H2O (distilled) 11 smal

10、l beakers 0.05 M NaCl 0.05 M CaCl2 0.05 M Na3P04 0.05 M HC2H3O20.05 M H3C6H5O7 M HCl M HNO3 0.05 M CH3OH (methanol) 0.05 M C2H6O2 (ethylene glycol) PROCEDURE 1. Do not press any button on calculator unless told to do so in the instructions. Caution: Handle the solutions in this experiment with care.

11、 Do not allow them to contact your skin. Notify the instructor in the event of an accident. 2. Assemble the conductivity probe, utility clamp, and ring stand as shown in Figure 1. Be sure the probe is clean and dry before beginning the experiment 3. Plug the Conductivity probe into the adapter cable

12、 and plug into channel. Make sure link between calculator and CBL is firmly seated into jack. 4. Turn on the Calculator. Press Prgm button and select Datamate to start program. Press enter twice. 5. Set up Calculator for the conductivity probe. · Press 1 for setup. · Using arrows select Ch

13、. 1. · Select 3: Conductivity · Select 5: 2000O(MICS) · Make sure no other channels have any sensors installed or shown, if they do see the instructor. · Select 1: OK · You will stay on the main screen and monitor the data at the top right comer of screen. 6. Put each of the

14、 solutions in a small beaker. Mark them with the molecular formula. 7. Measure the conductivity of each solution. · Carefully raise each beaker and its contents up around the conductivity probe until the hole near the probe end is completely submerged in the solution being tested. Important: Si

15、nce the two electrodes are positioned on each side of the hole, this part of the probe must be completely submerged as shown in Figure 1. · Briefly swirl the beaker contents. Monitor the readings on the calculator screen for 6-8 seconds, then record the conductivity value in your data table (ro

16、und to the nearest 1 µS) · Before testing the next solution clean the electrodes by surrounding them with a 250-mL beaker and rinse them with distilled water from a wash bottle. Blot the outside of the probe dry with a towel. It is not necessary to dry the inside of the hole near the probe

17、 end. 8. Put away the equipment and discard the solutions as directed: · Select 6: Quit · Press clear to clear screen · Turn off calculator · Disconnect conductivity probe and put it back into the box. · Place CBL unit in box · Return equipment to original location. DAT

18、A AND CALCULATIONS SOLUTIONS CONDUCTIVITYA- NaCl A-CaCl2 A- Na3PO4 B -HNO3 B -H3C6H5O7 B - HCI B HC2H3O2C - H20 (tap) C - H20 (distilled) C-CH3OH C - C2H6O2 PROCESSING THE DATA 1. Based on your conductivity values, do the Group A compounds appear to be molecular, ionic or molecular acids? Would you

19、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. Explain. 3. In Group B, do all four compounds appear to be molecular, ionic, or molecular acids? Classify each as a strong electrolyte or a weak electrolyte, and arrange them from the strongest to weakest, based on conductivity values. 4 . Write an equation for