Conductivity of Ionic and Covalent Compounds

If an ionic compound is dissolved in water, it dissociates into ions and the resulting solution will conduct electricity. An ionic compound is one that contains even one ionic bond. A covalent compound will contain all nonmetals and therefore all covalent bonds.

Dissolving solid sodium chloride in water releases ions according to the equation:

NaCl (s) + H2O (l) ---- Na+ (aq) +Cl- (aq)

Objectives:

●To investigate the conductivity of ionic compounds versus covalent compounds.

●To determine the effect of increasing concentration on conductivity.

●To identify two unknowns based on their relative conductivity.

When a conductivity 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), and this produces a conductivity reading. The unit of conductivity used in this experiment is the microsiemens per centimeter or µS/cm.

You will first measure the conductivity of distilled water (as a control), and then you will measure the conductivity of the NaCl (sodium chloride) solutions and C12H22O11 (sucrose) solutions at varying concentrations by changing the number of drops.

Hypotheses:

NaCl is a (ionic or covalent) compound so it is hypothesized that it (will or will not) produce an electric current.

C12H22O11 is a (ionic or covalent) compound so it is hypothesized that it (will or will not) produce an electric current.

You will also be measuring two unknown solutions to determine whether they are ionic compound solutions or covalent compound solutions. One of the unknowns is isopropyl alcohol and the other is calcium chloride.

Isopropyl Alcohol is C3H7OH - Is this an ionic or covalent compound

Calcium Chloride is CaCl2 – Is this an ionic or covalent compound?

Materials

LabQuest Unit and Conductivity ProbeNaCl
100mL Glass BeakerC12H22O11 sucrose
100 mL Plastic BeakerIsopropyl Alcohol solution
Distilled WaterCaCl2 solution
Wash bottlesPlastic Pipettes
Electronic ScaleWatch Glass
100 mL Graduated CylinderPaper Towels

Procedure (Some words have been underlined and capitalized below for emphasis. Please do not use these random capitalizations and underlining in your reports.)

Part 1: Sodium Chloride

  1. Place a watch glass on the electronic scale and zero the scale.
  2. Measure out 2.9 grams of NaCl and pour into a 100 mL Glass Beaker.
  3. Measure 50mL of distilled water using a Graduated Cylinder and pour into the100 mL glass beaker that has the NaCl.
  4. Stir the NaCl and Distilled Water Solution using the conductivity probe and then go to back sink and thoroughly rinse the probe with distilled water from a wash bottle.
  5. Measure another 75 mL of distilled water using a Graduated Cylinder and place in a fresh 100 mL Plastic Beaker.
  6. Plug the Conductivity Probe into the LabQuest Unit
  7. Place the Conductivity Probe into the center of the 100 mL Plastic Beaker,stir it around a bit and then hold it steady.
  8. Press the Red Box on the LabQuest Unit screen and click “Zero”
  9. Record the Value shown on Table 1 where it says 0 drops.
  10. Using a plastic disposable Pipette, place one drop of the NaCl solution from the 100 mL glass beaker into the 100 mL Plastic Beaker.
  11. Place the Conductivity Probe back in the center of the 100 mL Plastic Beaker, THOROUGHLY STIR and then hold steady and record the new value onto Table 1.
  12. Repeat steps 10-11 until Conductivity Values are found for drops 2-5.
  13. Dump all solutions in the sink and wash thoroughly all plastic/glassware. Use wash bottle of distilled water to do the final rinse of the conductivity probe.

Part 2: Sucrose

  1. Place the Watch Glass on the Electronic Scale and zero the scale.
  2. Measure 17.1 grams of Sucrose and place in a 100 mL Glass Beaker.
  3. Measure 50mL of distilled water using aGraduated Cylinder and pour into the100 mL Glass Beaker that already contains the sucrose.
  4. Stir the Sucrose and Distilled Water Solution using the conductivity probe and then go to back sink and rinse the probe with distilled water from a wash bottle.
  5. Measure 75 mL of distilled water using the Graduated Cylinder and place into the100 mL Plastic Beaker.
  6. Plug the Conductivity Probe into the LabQuest Unit.
  7. Place the Conductivity Probe into the center of the 100 mL Plastic Beaker and hold steady.
  8. Press the Red Box on the LabQuest Unit screen and click “Zero”.
  9. Record this value shown onto Table 1 where it says 0 drops.
  10. Using a fresh disposablePipette, place one drop of Sucrose solution from the 100mL glass beaker into the 100 mL Plastic Beaker.
  11. Place the Conductivity Probe back in the center of the 100 mL Plastic Beaker, THOROUGHLY STIR, and then hold steady and record the new value onto Data Table 1.
  12. Repeat steps 10-11 until Conductivity Values are found for drops 2-5.
  13. Dump all solutions in the sink and wash thoroughly all plastic/glassware. Use wash bottle of distilled water to do the final rinse of the conductivity probe.

Part 3: Unknown Solutions

  1. Obtain 1 pipette full of Unknown Solution 1 from teacher’s cart.
  2. Measure 75 mL of distilled water using the Graduated Cylinder and place in a 100 mL Plastic Beaker.
  3. Plug the Conductivity Probe into the LabQuest Unit.
  4. Place the Conductivity Probe into the center of the 100 mL Plastic Beaker and hold steady.
  5. Press the Red Box on the LabQuest Unit screen and click “Zero”.
  6. Record the Value shown onto the Data Table for 0 drops.
  7. Add one drop of Unknown Solution 1 into the 100 mL Plastic Beaker.
  8. Place the Conductivity Probe back in the center of the 100 mL Plastic Beaker, THOROUGHLY STIR, and the hold steady and record the new value onto the Table 1.
  9. Repeat steps 7-8 until Conductivity Values are found for drops 2-5.
  10. Dump all solutions in the sink and wash thoroughly all plastic/glassware.
  11. Repeat Steps 1-10 for Unknown Solution 2.

Results

Table #1 – Conductivity of Solutions with Increasing Concentrations

Solution /
0 Drops
/
1 Drop /
2 Drops
/ 3 Drops /
4 Drops
/ 5 Drops
Conductivity of NaCl (µS/cm)
Conductivity of C12H22O11 (µS/cm)
Conductivity of Unknown #1 (µS/cm)
Conductivity of Unknown #2 (µS/cm)

Lab Report Specifications and Hints – Conductivity of Ionic and Covalent Compounds

Introduction

Background topics should include a thorough discussion (at least 2 paragraphs) of ionic vs. covalent compounds – noting differences in properties, behaviors, etc. The introduction should also explain specifically WHY ionic compounds form ions when dissolved in water and how that relates to the property of conductivity. Be sure you have explained what conductivity is and how it can be measured. Note possible ways to measure conductivity and units like the microsiemens per centimeter or µS/cm that. Be sure to cite at least once per paragraph in APA format.

Include as always all objectives in past tense sentences. And also clearly include the lab hypotheses being careful to change them to past tense. (“was hypothesized” instead of “is hypothesized” for example since lab is now done!)

Methods

Use the given procedure, noting any changes or specific additions. Be sure to put in PAST tense, passive voice sentences and paragraphs (NOT STEPS!! NOT COMMANDS!) and make the sentences read well rather than use the exact brief language used by the sheets to be concise. Also don’t randomly capitalize or underline as the lab sheets did to help with emphasizing certain steps or words.

There are no calculations for this lab but you should include a short paragraph in your methods about your results manipulation steps which in this case includes a brief explanation about what was graphed and what kind of graph was created.

Results

You should have 1 large data table like the one above recreated. Include proper units of course.

You must also create a BAR graph (figure 1) that has 24 bars!!! You must follow the directions to create this graph in the “numbers” app or if you know how to do the same thing in Excel or google sheets you may do so. You may append your graph even though it is a computer made graph (just in case you have a hard time importing it into the rest of your lab text file). If you append, be sure to note that in your report as you would if it were handwritten and appended.

Discussion

Here are some hints for what you should discuss about your results….

●Using table 1 and figure 1, say whether NaCl is ionic or covalent and why and how the data (Table 1 and/or Figure 1) supports this fact. Be specific about the data evidence.

●Using table 1 and figure 1, say whether C12H22O12 is ionic or covalent and why and how the data (Table 1 and/or Figure 1) supports this fact. Be specific about the data evidence.

●Explain if hypotheses were correct and why based on above.

●Identify the unknowns (by#) as covalent compound isopropyl alcohol or ionic compound calcium chloride. Justify these identifications with results as evidence! Explain well!

●Explain the trends seen for increasing drops/concentration for the different solutions.

●Identify and discuss error sources that could have contributed to errors in this lab and what those errors would be.

●Clearly note if and how the objectives were met. (This can be done as you discuss the results above – it does not have to be at the very end of the discussion where it might seem redundant.)

●This discussion should be longer than usual since there are several objectives and a lot of data in this lab. I would suspect that you need 5 or 6 paragraphs at least and about at least 1 ½ pages to adequately explain all this asked for in this discussion.

References

APA format as always – use my 2 page guide!!