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Tracking Electrons.

Tracking Electrons.

Introduction: (Initial Observation)

Electrochemical processes have a practical importance in everyday life; most people take for granted the chemical reactions occurring inside the batteries that power our flashlights, toys, radios, and calculators. Electrochemical processes are also used in protective or decorative electroplating.

Although we cannot see electrons, their movements and their path, we know that in many chemical reactions electrons move between elements and between material.

The question is what path do electrons use in their movements? Do they travel in a straight path? Do electrons travel in a path that is shorter? Do they travel where there is less electrical resistance? How does voltage between electrodes affect the path of electrons? How does temperature affect the path of electrons?

How does the electrons movement path affect us and why it is important to be studied?

While ago when I was doing a copper plating experiment on a coin (US quarter), I noticed that some areas of the coin are plated better than others. In other words I did not get a uniform coating of copper on the coin. This can be a serous problem in both protective and decorative plating.

In this experiment I will study the path electrons choose while going through a fluid.

Dear

This project guide contains information that you need in order to start your project. If you have any questions or need more support about this project, click on the “Ask Question” button on the top of this page to send me a message.

If you are new in doing science project, click on “How to Start” in the main page. There you will find helpful links that describe different types of science projects, scientific method, variables, hypothesis, graph, abstract and all other general basics that you need to know.

Project advisor

Information Gathering:

Find out about electrons and their properties. Read books, magazines or ask professionals who might know in order to learn about chemical reactions that involve movements of electrons from one element to the other. Keep track of where you got your information from.

Following are samples of information that you may find:

You should be familiar with the color change of phenolphthalein, the formation of complexes, and oxidation-reduction reactions prior to doing your experiment.

How can you see electrons?

You can’t really see electrons directly, in the same way you can see a lump of carbon, say. On the other hand, you might say that when you’re looking at a lump of carbon, or any other element for that matter, it’s the electrons you’re seeing, since they are what interact with light, not the nucleus. And when you pick up a sample of any element, it’s the electrons you’re feeling, because it is electrostatic repulsion between the electrons in the sample and the electrons in you that cause it to push back at you when you squeeze it. In fact, every physical interaction you have with the world involves exclusively contact and forces between electrons, or electrons interacting with photons. (The only exception being when you pick up something radioactive.)

Although they are everywhere, it’s hard to bottle up a bunch of electrons and keep them as a sample. Hard, but not impossible: You can have them in a capacitor or stuck on a metal electrode in a vacuum and keep them there for months or years on end. But it looks sort of boring.

Source…

Anode: The electrode of an electrochemical cell at which oxidation occurs. The positive terminal of an electrolytic cell.

Cathode: the electrode of an electrochemical cell at which reduction occurs. The negative terminal of an electrolytic cell.

Turnbull’s blue: The double cyanide of ferrous and ferric iron, a dark blue amorphous substance.

Phenolphthalein

Phenolphthalein is an organic compound (C20H14O4) used as an acid-base indicator. The compound is colorless in acidic solution and pinkish in basic solution (with the transition occurring around pH 9).

Phenolphthalein does not dissolve very well in water, so for titrations it is usually prepared in alcohol solution. When adding a drop of indicator to an acid you will sometimes detect a slight cloudy white color. This is actually a precipitate of solid phenolphthalein, as the high local concentration exceeds the solubility product. It will usually disappear if you shake the solution, since enough solvent becomes available to dissolve the solute.

Phenolphthalein was used for many years as the active ingredient in Ex-Lax. However, recent (and controversial) concerns about its possible carcinogenicity have caused it to be replaced with other substances in laxatives. There is no health hazard from the minute quantities used in titrations.

In our experiment at the cathode hydrogen ions (H+) receive electrons and become hydrogen gas while OH- ions will accumulate and increase the pH of the solution. Phenolphthalein will cause a pink color in the pH of 9 and above.

2 H20(l) + 2 e- ==> 2 H2(g) + 2 OH-(aq) [pink with phenolphthalein]

If iron goes into solution, ferrous ions must appear. Ferrous ions with Ferricyanide, form the well-known Turnbull’s blue compound. That is why Ferricyanide is used as a reagent for Fe2+ ions.

At the anode where iron enters the solution and blue color is produced the following reactions are occurring:

Fe(s) ==> Fe2+(aq) + 2 e-

3 Fe2+(aq) + 2 Fe(CN)6(aq) [yellow] ==> Fe3[Fe(CN)6]2(s) [ “Turnbull’s blue”]

Question/ Purpose:

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.

The objectives of this experiment are to construct a simple electrochemical cell and to trace the path of the electrons involved in the reaction.

Additional question:

How does voltage between electrodes affect the path of electrons?

How does temperature affect the path of electrons?

Identify Variables:

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.

This is how you may define the variables

Independent variable (also known as manipulated variable) is the voltage between electrodes.

Dependent variable (also known as responding variable) is the electron path. Electron path will be observed using color reagents.

Constants are the composition of the electrolyte solution/gel and the distance between electrodes.

Controlled variable (optional) is the temperature inside the electrolyte solution/gel.

Hypothesis:

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.

This is a sample hypothesis for “the effect of voltage on the electron path”.

I hypothesize that electrons select the shortest path on a straight line. Increasing the voltage will change the path of electrons to a more narrow and concentrated path. I think the electrons will concentrate in the shortest path when the voltage is higher.

Experiment Design:

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.”

Experiment 1:

Introduction:

In this experiment two iron nails are connected to the terminals of 9.0-volt battery. The nails are inserted in a petri dish of clear gelatin to which color indicators have been added. The flow of electrons in the reaction can be traced by the color changes that occur. Color indicators that we will use are phenolphthalein and potassium Ferricyanide.

At the anode where blue color is produced the following reactions are occurring:

Fe(s) ==> Fe2+(aq) + 2 e-

3 Fe2+(aq) + 2 Fe(CN)6(aq) [yellow] ==> Fe3[Fe(CN)6]2(s) [ “Turnbull’s blue”]

At the cathode where a pink color is produced the following reaction is occurring:

2 H2O(l) + 2 e- ==> 2 H2(g) + 2 OH-(aq) [pink with phenolphthalein]

Procedure:

  1. Make gelatin according to package directions but add 10 drops of phenolphthalein and 10.0 mL of 0.1 M K3Fe(CN)6.
  2. Let the dish stand until gel is formed or overnight. You should observe initial color around each nail.
  3. Attach leads from the battery to two clean iron nails using alligator clips for the connections. Place the nails as far apart as possible head down in a petri dish to which the gelatin solution has been added.
  4. Draw a diagram showing the flow of electrons from one electrode through the battery to the other electrode.
  5. Take a picture of the gel dish after the electron path is revealed.

The gelatin and nails should be discarded with the solid waste.

Care should be taken when handling the K3Fe(CN)6 solution; cyanides are poisonous. Goggles must be worn throughout this experiment.

The image on the right shows the outcome of the test after 3 hours. The only difference is that instead potassium ferricyanide I have used ferrocyanide.

Experiment 2:

(Optional)

How does voltage between electrodes affect the path of electrons?

Repeat the above experiment with eight different voltages such as 3, 6, 9, 12, 15, 18, 21, and 24 volts. Compare the electron paths.

Experiment 3:

(Optional)

How does temperature affect the path of electrons?

Repeat the above experiment in 3 different temperatures of 0, 25 and 50ºC. Compare the electron paths. For this test, instead of gelatin gel, you must use agar gel. Agar gel will remain gel in a bout 50ºC while gelatin gel will liquefy at this temperature.

Materials and Equipment:

Chemicals

phenolphthalein solution (1 gram in 99 grams of ethanol)*
0.10 M K3Fe(CN)6 (Potassium Ferricyanide [hexacyanoferrate)III])
(3.30 grams K3Fe(CN)6 dissolved in distilled or deionized water and diluted to 100 ml)
plain gelatin
#4 ungalvanized iron nails

Equipment

sandpaper
9-volt battery
leads with alligator clips attached
600-mL beaker*
petri dish
10-mL graduated cylinder

Modifications/Substitutions:

  1. potassium Ferricyanide, Phenolphthalein and Phenolphthalein solution are available at ChemicalStore.com and some local scientific suppliers.
  2. Any suitable glass container may be used in place of the 600-mL beaker.
  3. A shallow plastic dish or jar lid may be used in place of the petri dish.

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.

Calculations:

You may need to calculate the molecular mass of K3Fe(CN)6 if you need to make 0.1 M solution without using the ratio suggested in the material section (above).

If you do any calculations, write your calculations in this part of your report.

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.

Conclusion:

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.

Possible Errors:

  1. Ungalvanized common nails with the largest possible head should be used.
  2. For more advanced students a variety of electrodes could be used. One example is to use copper electrodes in (NH3)aq gel.
  3. Aluminum nails will not work.

References:

This experiment is adapted from work done at 1985 I.C.E. Program at the University of California, Berkeley.

Merrill, P., Parry R.W., Tellefsen, R.L., and Bassow, H., Chemistry Experimental Foundations – Laboratory Manual, Prentice-Hall, Inc., Englewood Cliffs, NJ, 1982, p. 81.
– Describes an experiment which uses this chemical system in agar gel to demonstrate corrosion of iron.

http://www.owlnet.rice.edu/~chem152/lab152/ElectroGels/

Tests for iron ions (Iron reagent)

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