Editor’s note: The beautiful Miss Penny is back with another fun science activity, this time on electrolysis! Her new book “Miss Penny’s How to Be Creative With Science” also teaches you about various electrochemical DIY projects, such as etching on metal cups. Sounds cool, right? As makers, do you have any other ideas on how to apply this scientific technique?
By Miss Penny (陳乃綺)
Creative with Science: Electricity and Magnetism
Electricity is a basic daily resource, and electrical science is an important part of physics and chemistry in junior high school. Electricity is often seen together with magnetism, and electrochemical redox reactions and electromagnetism are also core exam subjects. Electrochemistry is the study of how electricity is applied in chemistry, which includes electrochemical cells, electroplating, electrolysis and etching. Electricity and magnetism are inseparable: for example, early CRT televisions worked by deflecting charged particles in magnetic fields.
Mei is curious about the stylus that came with daddy’s smartphone. It looks like any ordinary pen, but you can write on the screen with it. How is it possible to use the phone by just tapping the stylus on the screen?
Making an Electrical Cell from Water? Electron Transfer via Redox
Electrochemistry is a branch of chemistry focusing on chemical reactions involving electron transfer, such as electroplating, electrolysis and electrochemical cells. The redox reaction consists of electron transfer between different substances.
- Oxidation takes place when a substance loses electrons, resulting in an increase in its oxidation number.
- Reduction takes place when a substance gains electrons, resulting in a decrease in its oxidation number.
- The “oxidation number” is the hypothetical charge an atom would have if all bonds to atoms of different elements were ionic.
The whole redox reaction takes place at once. When one substance loses electrons, the other gains them. A substance that is oxidized is said to be a “reducing agent”, as it makes the other substance gain electrons and hence undergo reduction. Conversely, a substance that is reduced is an “oxidizing agent”, as it makes the other substance lose electrons and hence undergo oxidation.
We can determine in advance the potential for oxidation and reduction in any redox reaction. By looking at the relative reactivity of metals, we can tell which substance will oxidize, and which reduce. For example, iron has a higher reactivity than copper, so when an iron nail is suspended in copper sulfate solution (containing copper ions), the positive copper ions are reduced and become metallic copper, while the iron nail gradually dissolves into iron ions.
What does electron transfer do?
Plating is a process whereby the surface of an object is covered with a thin layer of metal. Different metals serve different plating purposes:
- Preventing corrosion: unreactive copper is plated onto a more reactive metal to protect it. E.g. keys.
- Decoration: objects plated with gold, silver or copper look nice and shiny. E.g. jewellery.
- Abrasion resistance: to protect the body of the object from wear. E.g. mobile phones.
- Increasing value and quality: an iron ring plated with gold looks just like a gold ring!
Electrolysis is a process of chemical decomposition produced by passing an electric current through a liquid or solution containing ions, leading to redox reactions and the separation of materials. During the electrolysis of water, the positive pole produces oxygen and the negative pole produces hydrogen. This pure hydrogen and oxygen can then be acquired by collecting the gases over water.
Many industrial materials are made using electrolysis; for example:
- Electrolysis of sodium chloride produces sodium metal at the negative pole and chlorine at the positive pole.
- Electrolysis of aluminum oxide produces aluminum metal at the negative pole.
- Part of the process of extracting metallic copper from copper ore involves electrolysis in order to remove oxygen and yield Electrolytic-Tough-Pitch (ETP) copper, which is purer.
A cell’s electrical energy is generated by electron transfer via redox reaction. If we connect an electrical appliance to the positive and negative poles of the cell and make a circuit, electrons begin to flow through the appliance and make it work. The longer the circuit is closed (i.e. the appliance is on), the more the substances inside the cell undergo redox reactions, and the less energy it has left, until finally there is nothing left.
1. The earliest battery
The earliest battery (i.e. collection of electrochemical cells) was the “Voltaic pile”, named after inventor Alessandro Volta. Volta took pieces of cloth that had been soaked in salt water and sandwiched them between discs of copper and zinc (which have different reactivities).
2. The earliest energy storage device
The earliest energy storage device was the previously introduced Leyden jar, which could be discharged only once before needing to be recharged. This makes it a capacitor, not a battery.
3. Rechargeable batteries
Many batteries used today can be used over and over again: e.g. car batteries, mobile phone batteries and all-purpose rechargeable batteries. When these batteries are recharged, they undergo electrolysis and so return to their original state, so they can be used again.
Fun With Science: Etch Your Name
Q-tips + brine + battery = DIY plating
Electro etching uses a redox reaction between brine and a metal. The Q-tip is moistened with brine and is used to oxidize the metal, which partially dissolves into metal ions and leaves a mark on the surface. You can create any shape or text you want!
What you need:
1. Concentrated brine
3. A 9V battery
4. A 9V battery holder
5. A spoon
6. Insulating tape
1. Take the positive wire of the battery holder and stick it to the bottom of the spoon using the insulating tape.
2. Wrap the negative wire around one end of the Q-tip.
3. Insert the 9V battery.
4. Moisten the Q-tip with brine and etch your name on the spoon. (You have to press hard!)
Etching can be wet or dry
Etching is the process of removing parts of a metallic surface to make patterns. There are two ways to do this: chemical wet etching and physical dry etching.
Wet etching uses chemical substances to induce redox. If electrical etching is used, the voltage needed increases as the reactivity of the metal decreases.
Dry etching exposes the metallic surface to a high-speed bombardment of negatively charged ions (fluorocarbons, oxygen, chlorine etc.), sometimes with the addition of noble gases (nitrogen, argon, helium…).
(Excerpt from “Miss Penny’s How to Be Creative With Science” by Miss Penny)