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Electrochemistry for Anodes and Cathodes

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I am not sure if I have the right out come for this experiment for the following questions

1. Which one is the anode or the cathode?
2. What happens when the flame reaches the open end of the pipet. What property does this show about hydrogen gas?
3. What happens when turmeric indicator is added and connected to the power. What does this tell you?

Turmeric indicator is prepared by measuring about 1 tablespoon of turmeric powder into a cup and adding isopropyl alcohol.


Experiment 8
Electrolysis of a Salt Solution

An apparatus for carrying out electrolysis will be constructed. Water will be decomposed into its constituent elements, the gaseous products of which will be tested for combustion.

Electrolysis is the process whereby a chemical change is produced by use of an electric current. A typical setup would include a source of direct current (such as a lead storage battery or even a dry cell), an anode (the electrode at which oxidation takes place), and a cathode (the electrode where reduction takes place).

One example of electrolysis is the electrolysis of an aqueous sodium chloride solution. The overall result is the production of hydrogen gas and chlorine gas. The following reactions describe this transformation:

This reaction works well for sodium chloride concentrations of 1 M or better. Concentrations of chloride less than 1 M will result in the formation of oxygen gas at the anode as a side reaction.

This experiment will involve the electrolysis of a sodium chloride solution using an easily constructed electrolysis apparatus. The hydrogen gas will be collected and tested for combustion. The chlorine gas is soluble in water (and, depending on what the electrode is made of, may react with the electrode) and will not be tested.

Note that chlorine gas could be collected after the solution is saturated with it. Chlorine will not be collected or tested in this experiment.




2 transparent plastic cups

2 electrodes (graphite, stick pins, nails, etc.)

table salt

1 dry cell (9V, also, 2 such cells will work faster)

4 to 6 alligator clips (depending on number of dry cells used, 4 for one or 6 for two)

wire (bell wire, speaker wire, etc.)

2 syringe test tubes


Cut off the bottom third of a transparent plastic cup. The bottom part of another cup should fit the resulting hole and should enable it to sit upright in the holder.

Note where the bottom part of the cup stopped inside the holder. Remove the cup.

Cut two small windows, one on each side of the holder, that will allow access to the bottom of the cup, which will sit in the holder.

Using another cup, punch two small holes, about an inch or so apart, into the bottom of the cup. The holes should be small enough that they will grip the electrodes (nails, etc.) when they are pushed through.

Insert the electrodes into the holes about half way and sit the cup inside the holder.

At this point, you may wish to spread out some newspapers and sit the apparatus on them in case of spills.

Melt some paraffin wax and pour a half centimeter deep layer of wax into the cup so the electrodes will be sealed and the cup will not leak. See the diagram below.

Prepare a saturated salt solution by adding as much salt as will dissolve at room temperature. Pour this solution into the cup with the electrodes until nearly full.

Fill a pipet syringe with water until it overflows. Use your thumb to seal the open end of the pipet and carefully invert the pipet under the salt water in the cup. As long as the open end of the pipet is under the salt water, the water inside the pipet will not run out.

Carefully place the pipet over an electrode and be sure it will stand up. You may wish to clip a clothespin onto the pipet such that the clothespin may rest on the edge of the cup and help hold the pipet upright.

Repeat this procedure with the second pipet over the remaining electrode.

When ready, clip the wires from the battery to the electrodes. You should immediately see bubbles issuing from one of the electrodes (which one, the anode or the cathode?)

Note that chlorine gas is soluble and you will not collect any of it before one of the pipets is full of the other gas, hydrogen.

When the hydrogen gas collecting pipet is empty (of water), disconnect the battery and carefully lift up on the pipet. Reach under the pipet and place your thumb over the opening tightly (still under water), so as to make a seal. Remove the pipet, but continue to hold it upside down (that is, thumbed end down).

Ignite a match and bring it close to the opening while removing your thumb (if you do not remove your thumb, don?t worry, you will when the match reaches it!).

Do this quickly, and observe what happens when the flame reaches the open end of the pipet. What property does this show about hydrogen gas?

Further Observations

Pour out the salt solution, wash the cup with the electrodes with distilled water, and then refill with the saturated salt solution.

Add a small amount of your turmeric indicator.

Connect the power and observe what happens. What does this tell you?

Repeat these experiments once more or as many times as is necessary to make the observations.

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Solution Summary

The electrochemistry for anodes and cathodes is provided. What happens when the flame research the open end of the pipet is determined.

Solution Preview

1. Which one is the anode or the cathode?
When two metal or graphite electrodes are dipped into the solution and a voltage is applied across them, the positive cations are attracted to the negative electrode (the cathode) and the negative anions move toward the positive ...

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