Name ______Date of Experiment______Period _____
Lab Partners ______
Electrolytes and Non-Electrolytes[1]
Introduction
Some substances, when dissolved in water or in a liquid state, have the ability to conduct an electrical current. These substances are called electrolytes. The quantity of current conducted is related to the number of ions that are present. Some substances ionize completely (100%) when dissolved in water. These conduct the most current and are therefore classified as strong electrolytes. Other substances ionize incompletely (less than 100%). In other words, some of the molecules ionize and some of them do not. These compounds conduct less current and are called weak electrolytes. Finally, some compounds dissolve, but do not form ions when dissolved. Since no ions are present, no electrical current can be conducted. These are called non-electrolytes.
Purpose
To classify compounds as strong electrolytes, weak electrolytes, or non-electrolytes by testing their conductivity in aqueous solution
Safety
Wear goggles at all times. Gloves are optional. Do not touch any chemicals with bare hands. Wash hands immediately if you get any materials on your hands. Secure lids on all containers when you are finished using them.
Materials
Reaction well plate, conductivity tester, pipette
Group A: chemicals solids
Sodium chloride (NaCl), copper (II) sulfate (CuSO4), sucrose (C12H22O11), sodium bicarbonate (NaHCO3), corn starch (C6H1206)n, potassium chloride (KCl), potassium iodide (KI)
Group B: chemical solutions
Hydrochloric acid (HCl), acetic acid (C2H4O2), ammonia (NH3), sodium hydroxide (NaOH), isopropyl alcohol (C3H8O)
Distilled water, tap water
Miscellaneous household liquids (time permitting)
Procedure
Part 1
- Buff the copper electrodes of the conductivity tester with steel wool. Insert the battery and turn it on.
- Begin by testing your distilled water for electrical conductivity. If it is conductive, get a fresh sample.
- Place your reaction well on a piece of paper and label the rows and columns as shown in the illustration below. This will help you organize your data table and avoid confusing your chemicals.
- Transfer samples of the Group A solids to the reaction well plate using a scoopula or spatula. Place a small amount of each solid (about as much as a grain of rice) in separate reaction wells. Clean your scoopula each time to avoid cross-contaminating the chemicals.
- Test each solid for conductivity and record your findings. Be sure to clean the conductivity leads between each test by rinsing with distilled water and wiping dry with a paper towel.
- Add approximately 1 mL (about one dropper full) of distilled water to each reaction well to dissolve each substance.
- Test each solution for conductivity and record your findings. Be sure to clean and dry the conductivity leads between each test.
- Test Group B solutions for conductivity. Transfer approximately 1.0 mL (1 dropper) of each solution into the reaction well plate. Take care not contaminate the solutions by mixing up the pipettes. Be sure to secure the dropper back on to the bottle. Record your findings in the data table.
- Finally, test distilled water and tap water.
- Clean up you lab area when finished.
- Based upon your findings, classify each substance as a strong electrolyte, weak electrolyte, or non-electrolyte. Your conductivity tester will help you. Record your findings in the data table.
Part 2
If time allows, test various common liquids for conductivity. For example, soft drinks, juices, coffee, pickle juice, liquid soap, etc. could be tested. Test whatever is available. Record your findings in a data table
- When completing the experiment, turn the conductivity tester off and remove the battery.
- Waste materials may be washed down the sink. Rinse the reaction plate with distilled water and dry with a paper towel.
- Return all items to their proper places.
Part 1 Data Table
Well Address / Formula of Substance / Conductivity of Solid 0, 1, 2, 3, 4 / Conductivity of Solution 0, 1, 2, 3, 4 / Strength of Electrolyte / Ionic or Molecular?
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
1 0 low or none, 1 low, 2, medium, 3 high, 4, very high
2 strong, weak, or non-electrolyte
3 Ionic substances are composed of metals and non-metals. Molecular substances are composed of non-metals only.
Analysis
Read pages 452 - 453 in your text and discuss the following questions. Base your answers upon your experimental data. Note any inconsistencies between your data and your reading.
- Did any of the electrolytes in group A conduct electric current in the solid form? Explain why or why not.
- In the data table, classify each compound as ionic or molecular. Ionic compounds are composed of metals and non-metals. Molecular compounds are composed of non-metals. For a compound to be an electrolyte, what must happen when it dissolves in water?
- When an ionic solid dissolves in water, water molecules attract the ions, causing them to come apart, or dissociate. The resulting dissolved ions are electrically charged particles that allow the solution to conduct electric current. The following chemical equations demonstrate this phenomenon.
Na2CO3(s) → 2Na+(aq) + CO3 2-(aq)
Write a similar chemical equation for two solid electrolytes other than the one above.
- Were any molecular (non-ionic) substances electrolytes? If so, which ones? Were they strong or weak electrolytes?
- Sucrose, cornstarch, and distilled water are known to be non-electrolytes. Did your testing confirm this? If not, explain your findings.
- Compare your results for tap water and distilled water. Did they test differently? If so, how do you account for this?
Group A
NaCl sodium chloride
Na2CO3 sodium carbonate
CuSO4 copper(II) sulfate
C12H22O11 sucrose
NaHCO3 sodium hydrogen carbonate
(C6H12O6)n corn starch
KCl potassium chloride
KI potassium iodide
Group B
0.10 M HCl hydrochloric acid
0.10 M HNO3 nitric acid
0.10 M C2H4O2 acetic acid
0.10 M NH3 ammonia
0.10M NaOH sodium hydroxide
C3H8O isopropyl alcohol
5
David Scott, 2009
Revised 12/15/2009
[1] Adapted from Wilbraham, et.al., Chemistry (Prentice Hall, 2008)458.