You probably know batteries from everyday life. No matter where and how, they can be found everywhere, but the real mother of all batteries is the Daniell element. It is the prime example when it comes to batteries and galvanic cells. You can find everything about it here!
General information about the Daniell element
That Daniell element is also called Daniell’s element and is a Galvanic cellthat from a copper and a zinc half cell consists. Chemical energy can be converted into electrical energy using the Daniell element.
Structure of the Daniell element
The Daniell element is a galvanic element. A galvanic element, also known as a galvanic cell, always consists of two half-cells, each with an electrode and the associated electrode electrolyte solution. These two half-cells are then connected to each other via a salt bridge. Basically, a galvanic cell converts chemical energy into electrical energy.
One of the electrodes always represents the anode of the system and one the cathode. At least one electron is always released at the anode and at least one electron is accepted at the cathode.
If you want to simplify the whole thing a bit, you can simply get the mnemonic “OMA” to help you. This indicates that oxidation, negative pole and anode belong together. Accordingly, reduction, positive pole and cathode also belong together here.
The Daniell element describes one of these galvanic elements, with the metals copper and zinc as the electrode metals. The corresponding solutions contain copper (CuSO4-) and zinc sulphate (ZnSO4-). The respective half-cells of zinc and copper are then connected by the salt bridge.
Standard potential and voltage of the Daniell element
The principle works by having a nobler and a less noble metal within a system. One electrode, which consists of the baser metal, tends to give off electrons to the electrolyte solution through oxidation. The more noble metal, on the other hand, preferentially accepts electrons during reduction from the electrolyte solution.
Before you can understand how this structure of the Daniell element works, you first have to understand what constitutes a noble and a base element. These are standard potentials of the individual half-cells of a galvanic element that indicate how much energy the half-cell generates.
A standard potential is a value that determines how much current (in volts) a half-cell delivers. For this purpose, a reference half-cell was named, namely the Normal hydrogen half cell. This was set as the zero point, which means that it does not emit any electricity on its own.
A half-cell of another element can now be connected to this normal hydrogen half-cell in order to determine the voltage and thus the standard potential.
You don’t always have to find out or calculate the standard potential yourself, because there is already a detailed table in which you can read the respective standard potentials.
For the Daniell element, which consists of copper and zinc, the standard potentials are as follows:
Cu/Cu2+: +0.34V
Zn2+/Zn: -0.76V
Now you can use these values to determine which is the more precious or less precious metal.
Because the nobler metals always have a higher/more positive value than the baser metals. The more noble metal always gains electrons, while the base metal emits electrons. So the negative value reflects the donation and the positive value the acceptance of electrons.
So, judging by the standard potentials, zinc is the less noble metal and copper is the more noble.
How the Daniell element works
Now that you know which element is nobler, you can easily understand how the Daniell element works.
Since the baser element always emits electrons, this must affect the zinc electrode here. This releases a zinc ion by splitting off two electrons.
The two free electrons and the zinc ion (Zn2+) are then transferred to the electrolyte solution. These electrons then migrate over the existing salt bridge to the half-cell of the copper. When the electrons migrate across the salt bridge, a stream of electrons is created, which can then be used as an electrical voltage and measured using a voltmeter.
The electrons then continue to flow into the half-cell of copper and there first into the electrolyte solution. The two electrons then react with the copper ions from the copper sulfate present there and result in a full copper atom, i.e. a copper atom without a charge:
The resulting copper is then deposited on the copper electrode.
The complete reaction equation of the Daniell element is then:
By constantly depositing atoms at the anode and adding atoms at the cathode, the volume of the anode-electrode is constantly decreasing while the volume of the cathode-electrode is constantly increasing.
Calculation of the stress of the Daniell element
To calculate the current you need the two standard potentials of the elements:
Cu/Cu2+: 0.34V
Zn2+/Zn: -0.76V
With these you can then easily calculate the current of the Daniell element.
To do this, simply plug the individual values into the following equation:
ΔE = E cathode – Eanode
ΔE = Ecopper – Zinc = 0.34V- (-0.76V) = 1.10V
For comparison: A standard battery has an average voltage of 2.0 V.
If is, then no reaction takes place. However, if is then the reaction takes place.
Using the Daniell element
Nowadays, the Daniell element is hardly used at all in everyday life. This is because there are now cheaper, more durable and, above all, more powerful galvanic cells or batteries and accumulators that are more suitable for everyday use and, above all, in industry.
With the discovery of the galvanic element, and hence the Daniell element, this was chiefly used in electric telegraphs.
Experiment with the Daniell element
Daniell Element – The Most Important
- The Daniell cell is a version of the galvanic cell.
- The Daniell element consists of the half-cells of zinc and copper.
- The reaction equation of the Daniell element is: .
- The transfer of electrons from the zinc to the copper creates a flow of electrons, which can be used and measured as a current.
- Nowadays, the Daniell element is mainly used in teaching as a model for the galvanic cell.
proof
- chemistry-lessons.de: Daniell element (09.09.2022)