Daniell galvanic cell

Recreate one of the earliest chemical electric cells!

Difficulty:
Danger:
Duration:
15 minutes
Experiment's video preview
Chemical formula

Reagents

Safety

  • Put on protective gloves and eyewear.
  • Conduct the experiment on the plastic tray.
General safety rules
  • Do not allow chemicals to come into contact with the eyes or mouth.
  • Keep young children, animals and those not wearing eye protection away from the experimental area.
  • Store this experimental set out of reach of children under 12 years of age.
  • Clean all equipment after use.
  • Make sure that all containers are fully closed and properly stored after use.
  • Ensure that all empty containers are disposed of properly.
  • Do not use any equipment which has not been supplied with the set or recommended in the instructions for use.
  • Do not replace foodstuffs in original container. Dispose of immediately.
General first aid information
  • In case of eye contact: Wash out eye with plenty of water, holding eye open if necessary. Seek immediate medical advice.
  • If swallowed: Wash out mouth with water, drink some fresh water. Do not induce vomiting. Seek immediate medical advice.
  • In case of inhalation: Remove person to fresh air.
  • In case of skin contact and burns: Wash affected area with plenty of water for at least 10 minutes.
  • In case of doubt, seek medical advice without delay. Take the chemical and its container with you.
  • In case of injury always seek medical advice.
Advice for supervising adults
  • The incorrect use of chemicals can cause injury and damage to health. Only carry out those experiments which are listed in the instructions.
  • This experimental set is for use only by children over 12 years.
  • Because children’s abilities vary so much, even within age groups, supervising adults should exercise discretion as to which experiments are suitable and safe for them. The instructions should enable supervisors to assess any experiment to establish its suitability for a particular child.
  • The supervising adult should discuss the warnings and safety information with the child or children before commencing the experiments. Particular attention should be paid to the safe handling of acids, alkalis and flammable liquids.
  • The area surrounding the experiment should be kept clear of any obstructions and away from the storage of food. It should be well lit and ventilated and close to a water supply. A solid table with a heat resistant top should be provided
  • Substances in non-reclosable packaging should be used up (completely) during the course of one experiment, i.e. after opening the package.

FAQ and troubleshooting

The diode doesn’t light up. What to do?

First, make sure that the diode is connected correctly: the black crocodile clip should be connected to a short “leg”, and the red clip to a long one.

Importantly, crocodile clips shouldn’t touch the other “leg” to avoid short-circuiting!

Then, check the connection between the crocodile clips, the zinc wire, and the copper plates. Rods and plates must be secured on the edges of the test tube.

Make sure that colorless zinc sulfate ZnSO4 solution is in the test tubes with the zinc wire, and blue copper sulfate CuSO4 solution is in the test tubes with copper plates.

The rods and the plates must be partially immersed in the corresponding solutions.

The absorbing stripe a salt bridge should connect the blue copper sulfate CuSO4 solution and the colorless zinc sulfate ZnSO4 solution.

Step-by-step instructions

To make two Daniell cells we will need four vials: one vial of copper sulfate CuSO4 and one vial of zinc sulfate ZnSO4 for each cell.

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Connect the vials through a salt bridge.

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Now take two copper Cu and two zinc Zn electrodes.

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Insert the electrodes into the metal salt solutions: copper electrodes in copper salt, zinc electrodes in zinc salt.

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Electrons will move through the wires from the more active metal (zinc) to the less active one (copper). This movement creates an electric current and makes the LED glow and the buzzer squeak. The zinc gradually dissolves, while copper ions Cu2+ from the copper sulfate precipitate on the copper electrode in the form of copper Cu.

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Disposal

Dispose of solid waste together with household garbage. Pour solutions down the sink. Wash with excess of water.

Scientific description

Why does the diode glow?

When a diode glows, it means that there is an electric current in the wires. In our experiment, the electricity is obtained from two galvanic cells, called Daniell cells. Such a cell consists of a solution of zinc salt with a zinc electrode in it, a solution of copper sulfate with a copper electrode in it, and a salt bridge connecting the two solutions. The working principle of this cell is based on the sufficient difference in reactivity between copper and zinc. Being a more reactive metal, zinc atoms readily give up two electrons, forming zinc ions Zn2+, which go in the solution:

Zn – 2e → Zn2+

These electrons migrate to the copper electrode, which develops a negative charge. It attracts positively charged copper ions Cu2+, which are present in the copper sulfate solution. They accept the electrons to form metallic copper, which precipitates on the surface of copper electrode:

Cu2+ + 2e → Cu0

Moving through the wires from zinc to copper, the electrons create an electric current, which flows through the LED and makes it glow, or through the buzzer to make it squeak.

What is the salt bridge for?

The salt bridge connects the two solutions so the ions from one solution can move to the other solution and vice versa. Without such an exchange, the electric circuit would not be closed, and the battery wouldn’t work.

Learn more

If we take a closer look at the cell, we will find that there are too many positively charged ions in the zinc sulfate solution, as well as too many negatively charged particles in the copper sulfate solution. When the salt bridge connects the solutions, the negatively charged ions can move from the copper sulfate solution to the zinc sulfate solution, while the positively charged ions go in the opposite direction. This closes the electric circuit.

Why do we use two cells in the experiment?

Two cells connected in series will provide enough voltage for the LED to glow. One cell has a voltage of approximately 1 V, while two of them yield twice as much. The two cells can also be connected in parallel; in this case, the voltage will remain 1 V, but another characteristic - the electric current efficiency, or amperage, will double.

That's interesting!

What was the first chemical source of electrical current?

An Italian researcher Alessandro Volta (his full name is Alessandro Giuseppe Antonio Anastasio Gerolamo Umberto Volta) was the first to come up with the idea to connect a copper plate and a zinc plate with a wire and then immerse then in a solution of an electrolyte. The latter is a compound that, when being dissolved, produces positively and negatively charged ions, i.e. in form of a solution it conducts electricity.

By the way, after Alessandro Volta was named a measure of electric potential difference. This measure is volt, an important unit for any electrochemist. In his work, Volta proved that such a system made from two plates and an electrolyte indeed produces electricity. Back then, it was a real breakthrough!

Volta has also demonstrated that several cells containing a zinc-copper pair may be connected together. And that’s how he created a “voltaic pile,” which was essentially the very first chemical source of electricity invented. Since then, a voltaic pile allowed other researchers to work in a wide range of voltages. The pile consisted of alternated copper and zinc plates, and each pair of plates had a piece of woolen tissue soaked in electrolyte solution inserted in between. You can see how the construction of the voltaic pile looked like in the following video:

Here, an electrolyte may be a solution of a strong acid (HCl, H2SO4), alkali (KOH, NaOH) or salt (NaCl, ZnSO4). In a solution, all these compounds dissociate into charged particles – ions. They would serve as charge carriers, so that a charge could “migrate” from zinc to copper. Simply clumping pieces of zinc and copper together would not work: a transition would only take place only on contact points between two metals. Such a system would not be any different from an ordinary piece of metal.

Interestingly, a voltaic pile of a huge size (containing over 2,100 pairs of plates in one device!) possesses such a power that it creates an electric arch – a phenomenon causes by air ionization because of a high current source. Molecules in air (mostly N2 and O2) are normally neutral. However, when they bump into leads connected to such a huge voltaic pile, these molecules become ionized – they accept or donate electrons. This process goes on like an avalanche and creates around a whole area of ionized air – plasma, which conducts electricity.