Lab Report #8 PDF

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EXPERIMENT

8

Electrical Conductivity of Aqueous Solution Sabrina Castro ∙ April 13th, 2020 Dr. Q Meng ∙ Chemistry 1105 S51

Objective: The goal of this experiment observe the electrical conductivity of substances in aqueous solutions. Observing the electrical conductivity of substances will reinforce the ability to determine whether an aqueous solution is a strong or weak electrolyte. Through the observations of the aqueous solution conductivity, chemical reactions will be able to be interpreted. This experiment will enhance proficiency in writing net equations. Introduction: Electrical conductivity is based on the flow of electrons. Metals are good conductors of electricity because they allow electrons to flow through the metal. Distilled water is a very weak conductor because very little electricity passes through pure water. However, when a substance dissolves in water and forms ions, the ions are capable of conducting an electric current. If the substance is highly ionized, the solution is a strong conductor of electricity. If the substance is only slightly ionized the solution is a weak conductor. Strong acids and salts are strong electrolytes because they completely ionize (dissociate or separate) in solution. The ions carry the electric charge through the solution thus creating an electric current. The current, if sufficient enough, will light one or both LEDs on a conductivity meter, shown at right. This experiment will involve the testing of electrical conductivity. Substances will be tested by the use of the

conductivity apparatus. A bright glowing light will mean the solution has strong electrolytes, while a dim light will signify weak electrolytes. Materials:                    

Conductivity apparatus Small, dry beakers (6) Glass stirring rod Wash bottle with distilled water Sodium chloride, solid NaCl Calcium carbonate, solid, CaCO3 Calcium chloride, solid CaCl2 Hydrochloric acid, 0.1 M HCl Acetic Acid, 0.1 M HC2H3O2 Nitric acid, 0.1 M HNO3 Sodium hydroxide, 0.1 M NaOH Ammonium hydroxide, 0.1 M NH4OH Potassium iodide, 0.1 M KI Aluminum nitrate, 0.1 M Al(NO3)3 Magnesium Hydroxide, Mg(OH)2 Copper (II) Sulfate, 0.1 M CuSO4 Calcium Nitrate, 0.1 M Ca(NO3)2 Sulfuric Acid, 0.1 M H2SO4 Barium hydroxide, 0.1 M Ba(OH)2 Straw

Procedure: A. Conductivity Testing – Evidence for Ions in Aqueous Solution 1. Pour 25 mL of distilled water in a small dry beaker and test the conductivity. Pour about 25 mL of tap water in a small dry beaker and test the conductivity. 2. Place about 0.5 g of solid NaCl in a small dry beaker and test the conductivity. Add distilled water, stir, and retest the conductivity. 3. Place about 0.5 g of solid CaCO3 in a small dry beaker and test the conductivity. Add distilled water, stir, and retest the conductivity. 4. Place about 0.5 g of solid CaCl2 in a small dry beaker and test the conductivity. Add distilled water, stir, and retest the conductivity. 5. Test the conductivity of each of the following in a small beaker. (a) ~ 10 mL hydrochloric acid, 0.1 M HCl (b) ~ 10 mL acetic acid, 0.1 M HC2H3O2 (c) ~ 10 mL nitric acid, 0.1 M HNO3 (d) ~ 10 mL sodium hydroxide, 0.1 M NaOH (e) ~ 10 mL ammonium hydroxide, 0.1 M NH4OH (f) ~ 10 mL potassium iodide, 0.1 M KI (g) ~ 10 mL aluminum nitrate, 0.1 M Al(NO3)3 (h) ~ 10 mL magnesium hydroxide, saturated Mg(OH)2

(i) ~ 10 mL copper (II) sulfate, 0.1 M CuSO4 (j) ~ 10 mL Calcium nitrate, 0.1 M Ca(NO3)2 B. Conductivity Testing—Evidence for a Chemical Reaction 1. Test the conductivity of 0.1 M HC2H3O2 and 0.1 M NH4OH in separate beakers. Pour the solutions together and retest the conductivity. Record your observations and conclusions in the Data Table. Balance the equation for the reaction and write the total ionic and net ionic equations. 2. Test the conductivity of 0.1 M H2SO4 and 0.1 M Ba(OH)2 in separate beakers. Add 10 drops of 0.1 M H2SO4 into a beaker containing ~25 mL of distilled water. Continuously test the conductivity while adding Ba(OH)2 dropwise until the conductivity is minimal. Record your observations and conclusions in the Data Table. Balance the equation for the reaction and write the total ionic and net ionic equations. 3. Test the conductivity of distilled water while blowing CO2 through a straw in the water. Add 10 drops of 0.1 M Ba(OH)2 into a beaker containing ~25 mL of distilled water. Continuously test the conductivity while blowing through a straw until the conductivity is minimal. Record your observations and conclusions in the Data Table. Balance the equation for the reaction, and write the total ionic and net ionic equations. C. Net Ionic Equations- A Study Assignment Balance the following neutralization reactions; write the total ionic and net ionic equations. 1. Strong Acid and Strong Base HCl(aq) + NaOH (aq)  NaCl +H20(l) 2. Strong Acid and Weak Base HCl(aq) + NH4OH (aq)  NH4Cl (aq) + H20(l) 3. Weak Acid and Strong Base HF(aq) + NaOH(aq)  NaF(aq) + H20(l) 4. Weak Acid and Weak Base HF(aq) + NH4OH (aq)  NH4F(aq) + H20(l) Results: At the start of the video we can tell the two criteria that have to be met in order to be an electrolyte is something has to be dissolved and that something that is dissolved must ionize and if those criteria are not met we will not have an electrolyte, then those that dissolve and ionize a little will be a weak electrolyte and those that ionize a lot will be a strong electrolyte. Now when distilled water was tested for conductivity it did not produce electricity, since nothing dissolved, nothing can ionize. But when tap water was tested for conductivity the light bulb lit up and was able to conduct electricity. Furthermore, when Epson salt was tested for conductivity with a 34 watt bulb it produced light and with a 100 watt light bulb it was extra bright which was a strong electrolyte since salts dissolve and ionize very well and Epson salt does not which is why a dim light appears. Now when Ethanol was tested for conductivity with a 34-watt bulb ethanol did not create any light since it is pure and when solid NaCl was tested for conductivity nothing happened as well since it is not dissolved. Therefore, when NaCl solution was tested for conductivity with a 34-watt bulb it produced a bright light since it is dissolved and as well with a 100-watt bulb. But when NaCl in ethanol was tested for conductivity it did not produce any light since salt and ethanol do not dissolve which does not let it ionize. Therefore, when sucrose in ethanol was tested for conductivity, both sucrose and ethanol are not an electrolyte, so nothing happened since it did not ionize even if it did dissolve a little bit. Then when HCl acid was tested for conductivity with a 34-watt bulb it produced an extremely bright light that it even popped & with a 100 watt it produced an extremely bright light that created a spark. But when NaOH base

was tested for conductivity with a 100-watt bulb it produced a bright light which makes it a strong base. Now when ammonia (window cleaner) base was tested for conductivity with a 100watt bulb no electricity was produced but with a 34 watt it produced a dim light which we can conclude is a weak base since it dissolved but does not ionize well. Therefore, when vinegar was tested for conductivity it produced the dimmest light which makes it a weak acid and when Pepsi Coke was tested for conductivity it produced a dim light which makes it a weak acid as well. Lastly, when G-drink was tested for conductivity with a 34 watt it produced a dim light which was a weak electrolyte.

Prelab Quiz 1) When ionic compound NaCl dissolves in water, it produces Na+ ion and Cl- ion. 2) When covalent compound C6H12O6 dissolves in water, it produces A . A) C6H12O6 molecules B) C6 cation C) O6 anion D) H12 anion 3) Please classify the following compounds as “electrolyte”, “weak electrolyte” or “non electrolyte” KCl- Electrolyte, gasoline(C8H18)-non electrolyte, Ethanol- non electrolyte, AgI- weak electrolyte, BaSO4 – weak electrolyte, HNO3 - Electrolyte, HBr - Electrolyte, KOHElectrolyte

Discussion: Various solutions underwent a conductivity test. After watching the video, the results were as follows: Distilled water no conductivity, therefore since it is pure nothing can dissolve or ionize, while tap water gave a bright glow, meaning it had strong electrolytes. For the solid NaCl, it did not give off any light, however when the solids were mixed in a water solution NaCl had strong glows of light and strong electrolytes, while NaCl in ethanol it did not produce any light. Hydrochloric acid with a 34-watt bulb it produced an extremely bright light that it even popped & with a 100 watt it produced an extremely bright light that created a spark. Now with Pepsi it emitted a dim light, therefore it had weak acid. Ammonium (window cleaner) base was tested for conductivity with a 100-watt bulb no electricity was produced but with a 34 watt it produced a dim light which we can conclude is a weak base since it dissolved but does not ionize well. But when NaOH base was tested for conductivity with a 100-watt bulb it produced a bright light

which makes it a strong base and vinegar is considered a weak acid. Lastly, when G-drink was tested for conductivity with a 34 watt it produced a dim light which was a weak electrolyte. Conclusion: The goal of this experiment was to know, determine and prove which substances are capable to conduct electricity and which substances can’t conduct electricity and if any of the following substances can conduct electricity by submerging two copper wires connected to a battery that powers up a light bulb when electric current is present, and the copper wire conduct it. The brightness of the light emitted dictated whether the solutions had weak or strong electrolytes. Weak electrolytes produced a dim light, while strong electrolytes produces a bright light. Tap water and Gatorade gave a dim light which is a weak electrolyte. Vinegar and Pepsi are weak acids which caused them to give a dim light. HCl produced a bright light which is a strong acid. NaOH produced a bright light which makes it as strong base and ammonia produced a dim light which makes it a weak base. When two substances with weak electrolytes are mixed, they while produce a solution with weak electrolytes. The same applies to substances with strong electrolytes, however when one of each strong and weak electrolyte are mixed, the result will be a bright light with strong electrolytes. Human errors may occur while conducting the electrical conductivity test. Perhaps confusion with identifying chemicals may occur, so a second trial would be recommended to reinforce the results. There are ways to eliminate this issue. The experiment may include more trials or utilize a different device to measure the conductivity, for the most accurate results....