Introduction: (Initial Observation)
Electrolysis is one of the methods used to break molecules to their elements. For example we use electrolysis of water to make Hydrogen and Oxygen gasses. Also electrolysis of molten Sodium Chloride (or table salt) produces chlorine gas and Sodium metal. Electrolysis can also help us to learn more about chemicals, their elements and the strength of their ionic bounds.
In this project we will perform the electrolysis of potassium iodide solution to see the results!
Unlike Hydrogen and oxygen, both iodine and potassium are solids, so they can not exit the solution like gases. So what will happen to the potassium and iodine produced in this process? What will be the product of electrolysis of Potassium Iodide?
Find out about potassium iodide and electrolysis. Read books, magazines or ask professionals who might know in order to learn about the effect of electrolysis on different chemicals. Keep track of where you got your information from.
ELECTROLYSIS AND ITS APPLICATIONS:
You should know the following :-
When substances which are made of ions are dissolved in water, or melted, they can be broken down (decomposed) into simpler substances by passing an electric current through them. This process is called electrolysis.
When an ionic substance is melted or dissolved in water the ions are free to move about.
During electrolysis, positively charged ions – for example, metal ions – move to the negative electrode, and negatively charged ions move to the positive electrode.
During electrolysis, gases may be given off, or metals deposited at the electrodes.
During electrolysis, ions gain or lose electrons at the electrodes. Electrically neutral atoms or molecules are released.
Reactive metals such as aluminum are extracted by electrolysis.
The raw materials for producing aluminum are purified aluminum oxide and cryolite. Because aluminum oxide has a very high melting point it is dissolved in molten cryolite at a much lower temperature. The electrodes are made of carbon (graphite). The aluminum forms at the negative electrode and oxygen forms at the positive electrodes. This makes the positive electrodes burn away quickly so that they frequently have to be replaced.
Copper can be purified by electrolysis using a positive electrode made of the impure copper and a negative electrode of pure copper in a solution containing copper ions..
The electrolysis of sodium chloride solution (brine) is an important Industrial process. Chlorine gas is formed at the positive electrode and hydrogen gas at the negative electrode. A solution of sodium hydroxide is also formed. Each of these products can be used to make other useful materials:
- chlorine is used to kill bacteria in drinking water and in swimming pools, and to manufacture disinfectants, bleach and the plastic (polymer) PVC;
- hydrogen is used in the manufacture of ammonia and margarine;
- sodium hydroxide is used in the manufacture of soap, paper and ceramics.
At the negative electrode positively charged ions gain electrons (reduction).
At the positive electrode negatively charged ions lose electrons (oxidation).
In a chemical reaction if oxidation occurs reduction also occurs. These reactions are called Redox reactions.
Possible experiments include :-
Electrolysis of acidified water.
Electrolysis of aqueous solutions with electrode products being collected and tested where possible.
Electrolysis of lead bromide.
What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.
What are the products of electrolysis of Potassium Iodide?
The purpose of this project is to perform the electrolysis of Potassium Iodide and analyze the results to find out how does this process work!
When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.
We are not going to perform any quantitative test, so we do not need to identify variables. We are more interested on knowing what is the result, not the rate of result.
If we were interested on the rate of production, we could study the effect of any specific variable such as voltage or temperature on the rate of production.
Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis.
My hypothesis is that initially potassium metal may be formed on the anode (negative pole), but it will immediately react with water and become potassium hydroxide. I also think that Iodine will be released on the cathode (positive pole) and will dissolve in the potassium iodide solution.
Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”
Objective: To electrolyze a potassium iodide solution.
- phenolphthalein indicator (ChemicalStore.com)
- alligator clips (4)
- 9-Volt or 6-Volt battery (Hardware store)
- insulated wire
- solid potassium iodide (ChemicalStore.com)
- carbon electrodes (two pencils sharpened at both ends)
- shallow bowl (clear glass or white plastic)
- white paper
- Add some KI to the bowl, fill it half full with water and stir until the KI is dissolved. Put a white piece of paper under the bowl if it is a glass bowl.
- Add 5 drops of phenolphthalein indicator (instructions below).
- Connect the wire to the alligator clips. Clip one alligator clip to the tip of the pencils.
- Attach the other ends of the wires to the battery.
- Place the electrodes in the bowl so that the pencil tip is in the solution.
- Observe the electrodes for evidence of reaction. A few drops of the phenolphthalein indicator near the cathode will increase the pink color if the solution is too dilute.
Phenolphthalein or phenolphthalein solution are available from ChemicalStore.com and other suppliers of laboratory chemicals. If you are using pure phenolphthalein, you must dissolve it in alcohol prior to use. Dissolve one gram phenolphthalein in 100 ml ethyl alcohol or isopropyl alcohol.
In older version of this project guide we suggested using Ex-Lax tablets as a source of phenolphthalein; however, since then Ex-Lax tablets are discontinued.
Following is the old procedure for making phenolphthalein solution using Ex-Lax tablets.
- Ex-Lax tablects (2)21
- glass jar
- 2-propanol (rubbing alcohol)
- measuring spoons
- hammer or heavy blunt object
- Wrap the Ex-Lax tablets in some wax paper and crush them.
- Add 30 mL 2-propanol to the jar.
- Add the phenolphthalein or powdered tablets to the jar and stir.
Experiment Details and pictures:
In this experiment I used a petri-dish, two pencils, some connection wires with alligator clip leads and a 6 volt battery known as lantern battery.
I filled the petri dish with potassium iodide solution and a few drops of phenolphthalein solution.
I placed the petri dish in the middle of a plexi glass stand.
I stripped the ends of the pencils and attached them to the battery.
I placed the other ends of the pencils in two opposite ends of the petri-dish.
In a few seconds I could see the brown iodine on the positive electrode and hydrogen bubbles on the negative electrode.
Gradually the entire solution around the negative electrode became pink.
I later dropped a small piece of potato in to the petri dish in the brown area. It’s color changed to dark blue. Since potato has starch, this is a positive test for presence of iodine. I also dropped a small piece of copy paper in the iodine area of petri-dish and that turned to blue as well. In other words, copy paper also contain starch.
I tested a few different types of paper and noticed that most papers have starch. (Coffee filter papers don’t have starch).
Can I use metal electrodes instead of graphite?
I setup the experiment as described above, but used aluminum as electrodes and some new ex-lax tablets as phenolphthalein.
After connecting the circuit, bubbles started on negative electrode and solution around that electrode became basic (I used a pH paper to test it). However no brown iodine appeared on the positive electrode and no pink appeared in the negative pole.
I think what happened is that Iodine is reacting with aluminum and producing a colorless substance. I also think that possibly this special Ex-lax that I used did not contain phenolphthalein.
I continued my search and found the following news at CNN website.
The maker of best-selling Ex-Lax laxatives is pulling from the market all versions of the medication containing phenolphthalein, an ingredient the U.S. Food and Drug Administration wants to ban.
I also got a strip of phenolphthalein and two wide flat pencils in order to repeat the experiment.
Materials and Equipment:
List of material can be extracted from the experiment section. This is a sample list of materials:
- phenolphthalein indicator (ChemicalStore.com)
- alligator clips (4) (Electronic stores, Hardware stores)
- 9-Volt or 6-Volt battery (Hardware store)
- insulated wire (Electronic stores, Hardware stores)
- solid potassium iodide (ChemicalStore.com)
- carbon electrodes (MiniScience.com and ChemicalStore.com) I used two pencils sharpened at both ends instead.
- shallow bowl or petri-dish (clear glass or white plastic) (MiniScience.com)
- white paper
Results of Experiment (Observation):
Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.
Your results may include the following:
Electrolysis is a process by which a chemical reaction is carried out by means of the passage) of an electric current. As the reaction proceeds iodide is oxidized at the anode (negative) while water is reduced at the cathode (positive).
2I—>(aq) I2(s) + 2e-
2H2O(l) + 2e- –> 2OH-(aq) + H2(g)
net reaction: 2I-(aq) + 2H2O(l) –>I2(s) + 2OH-(aq) + H2(g)
The cathode will be recognized by bubbles (H2) on the electrode and pink phenolphthalein indicator from hydroxide production. Phenolphthalein turns pink in the presence of base and clear in the presence of acid. A slight yellow/brown color to the water around the anode may be observed. This is due to a small amount of iodine being dissolved in the Water.
No calculation is required for this project.
Summary of Results:
Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.
It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.
Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.
Related Questions & Answers:
What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.
If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.
If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.
Any chemistry book with a discussion on electrolysis may be used as a reference for this project.
Q. How do I measure and graph this experiments?
A. This project does not require any measurements. Results are visual. No graph is required. If you really need to have measurements and graph, you must modify the purpose or question of the project to one of the following:
- How does the voltage affect the rate of electrolysis in potassium iodide?
- How does the temperature affect the rate of electrolysis in potassium iodide?
For changing the voltage you will need a DC power supply that is able to provide different voltages.
For changing the temperature, you can place your test container on ice or on a warm surface.
Either way you measure the time needed for the purple color to progress certain length (I suggest 10mm or 1/2″) towards the opposite side.
How does the voltage affect the rate of electrolysis in potassium iodide?
Voltage is one of the factors that may affect the speed of electrolysis process. This can be tested in a simple experiment.
Variables: Independent variable is the voltage. Dependent variable is the time for a certain amount of electrolysis.
- In a 400ml beaker add 100ml cold water, 2 grams of potassium iodide and 2 grams of Agar gelling agent. Start to heat it up over an electric heater and continue stirring until the entire agar and potassium iodide dissolve and you get a clear liquid. This may require boiling for a few minutes. Continuous stirring is required.
- Add 10 drops of Phenolphthalein indicator to the solution and stir.
- Transfer the solution to a 4 or more petri-dishes. To each petri-dish add enough solution to cover the bottom. Dispose of the remaining solution or save it for repeating the experiments (if needed).
- Leave them in a cold place so that the gel will form.
- Insert two graphite electrodes in two opposite ends of each petri dish.
- One petri dish will be the control. Do not connect the electrodes to battery.
- The second petri dish is for 6-Volt. Connect the electrodes to the poles of a 6 volt battery.
- The third petri dish is for 12-Volt. Connect the electrodes to the poles of a 12 volt battery. (if you don’t have a 12-volt battery, link 2 6-volt batteries in series).
- The fourth petri dish is for 18-Volt. Connect the electrodes to the poles of an 18 volt battery. (if you don’t have an 18-volt battery, link 3 6-volt batteries in series).
- Record the time it takes for the pink gel to reach to the brown gel.
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