Chapter 1 - History Flashcards
How is a Leyden jar designed?
A glass jar with a conducting tin foil coating the inner and outer surface. Stops far enough down to prevent arcing between the foils. A rod penetrates the stopper of the mouth of the jar, and is electrically connected (usually by chain) to the inner foil.
The jar is charged by an electrostatic generator connected to the inner electrode, while the outer foil is grounded. Inner and outer surface stores equal but opposite charges.
Who coined the term “battery”?
Benjamin Franklin - as a term for combining several Leyden jars
Who was the first to connect several Leyden jars in parallel to increase the total stored energy?
Danial Gralath
According to Faraday, how many Leyden jars would be required to electrolyse a grain of water?
~800.000
Is a Leyden jar a battery?
No, a capacitor.
What is the nature of the dispute between Luigi Galvani and Alessandro Volta on the nature of electricity?
Galvani held the view that twitching of the frog’s leg was due to electricity generated by living tissue.
Volta thought the twitching was caused by electricity generated from a physical cause, not from the life of the frog.
What settled the dispute between Volta and Galvani on the nature of electricity?
The construction of the Voltaic pile. This showed that elecitricity was not something solely generated by living things.
Who is considered the inventor of the electrochemical battery?
Alessandro Volta
What was the Votalic pile?
A stack of discs of two metals - silver and zinc. The discs were separated by a piece of cloth or cardboard that has been soaked in salt water. This stack would create a small electric current that could be drawn off through wires and used for experiments.
Where does the energy for the Voltaic pile come from? (ie. how is it charged?)
Through the purification of elements. The reactions during discharge are spontaneous and we require energy to reform the pure metals.
What was the limiting factor that killed the Voltaic pile?
Hydrogen bubbles forming and reducing contact.
What is reduction?
A chemical species gaining an electron (positive charge is reduced).
What is oxidation
A chemical species is loosing an electron (positive charge is increased)
What is the positive electrode?
The electrode with the highest electrical potential (during discharge) and where a positive charge would have the highest energy. Source of positive charge.
What is the negative electrode?
The electrode with the lowest electrical potential (during discharge), where a positive charge would have the lowest energy. Source of negative charge.
What is the anode?
The electrode where the oxidation occurs. Electrons leaves the anode.
What is the cathode?
The electrode where the reduction occurs. Electrons enters the cathode.
What is the source of confusion between the term “negative electrode” and “anode”, and “positive electrode” and “cathode”?
We usually talk exclusively cathodes and anodes during both charge and discharge. The terminology is technically only correct during discharge.
Since the cathode and anode are defined from what type of reactions occurs, what we usually term the “cathode” is actually, by definition, the anode during charge.
However, what we call a cathode is always the positive electrode, so a more correct term would be to call the cathode the positive electrode, and the anode the negative electrode.
Describe the setup of a typical lemon battery experiment.
Use electrodes of different metals, e.g. zinc and copper. Connect in a lemon and hook up to a multimeter.
On the zinc side the following reaction is happening:
Zn -> Zn2+ + 2e-
The electrodes move through the current and reacts with H+ ions (from the citric acid) to form H2-gas:
2H+ + 2e- -> H2
Modifications:
1) Show that you short the battery by letting the electrodes touch.
2) Switch to a potato to show that other things functions as electrolyte as well.
3) Change to beaker - gather the hydrogen formed at the cathode. Put on fire.
4) Add zinc salt to prove that zinc participates in the reaction.
5) Add copper salt to prove that copper is not involved in the reaction.
6) Change metals for the electrode to notice changes in voltages.
7) Change the surface area of the electrodes to notice changes.
8) Notice changes over time.
What is Faraday’s big contribution to electrochemistry?
His quantification of the relation between the mass of the materials involved and the total charge transferred. This meant that an electrochemical battery has a limited charge.
What is Faraday’s 1st Law of Electrolysis?
The mass of a substance altered at an electrode during electrolysis is directly proportional to the quantity of electricity transffered at that electrode.
What is Farday’s 2nd Law of Electrolysis?
For a given quantity of direct current electricity, the mass of an elemental material altered at an electrode is directly proportional to the element’s equivalent weight.
Describe the Daniell cell.
Consists of copper and zinc electrodes immersed in solution of copper(II) sulfate (CuSO4) and zinc sulfate (ZnSO4) respectively. Originally sulphuric acid was used instead of zinc sulfate.
The two containers are connected by a salt bridge.
At the anode we get the oxidation: Zn -> Zn2+ + 2e-
At the cathode we get the reduction: Cu2+ + 2e- -> Cu
What is a gravity cell?
A version of the Daniell cell where the electrolytes are separated by gravity due to their different densities. Became the industry standard for the electric telegraph.
