GENERATING ELECTRICITY
Background info:
In redox reactions there's always an element that loses electrons (oxidation) and another who receives them (reduction), and as it is a reaction, energy is released.
Redox couples, like Cu (reducing agent) and Cu+2 (oxidating agent) are clear examples of redox reactions.
When we want to travel, we pay to an airline in order to them to take us in an plane, this means that, if we want to travel, we have to pay. But the pilot in the plane doesn't have to pay (and he maybe doesn't want to travel, but it is his job, so he must do it). With this metaphor we want to explain what is going to happen in the experiment we performed.
But, why does this happens? at first we need to know that current is the flow of electrons, while electricity is the process that involves the whole factors (voltage, current, impedance...), electrons always move from the negative to the positive pole, although we can have differences in the intensity of this flow, in galvanic cells, which are what we are creating in this lab session, the consist of two pairs of redox couples (they are formed by the oxidized and reduced form of an element, for example Cu+2/Cu0), and each of them will act as each of the poles of the battery. what we do in the galvanic cell is separating the two parts of the redox reaction, and connect them by an external circuit, allowing electricity to happen.
But, why does this happens? at first we need to know that current is the flow of electrons, while electricity is the process that involves the whole factors (voltage, current, impedance...), electrons always move from the negative to the positive pole, although we can have differences in the intensity of this flow, in galvanic cells, which are what we are creating in this lab session, the consist of two pairs of redox couples (they are formed by the oxidized and reduced form of an element, for example Cu+2/Cu0), and each of them will act as each of the poles of the battery. what we do in the galvanic cell is separating the two parts of the redox reaction, and connect them by an external circuit, allowing electricity to happen.
Water (H2O) is not a great conductor, but why does it always acts as a great conductor in films? that's easy to explain: water that contains NaCl (table salt), is composed of ionic bonds and its function is of making an ionic equilibrium between the two couples, as there is a difference in the potential of the two parts of it, this difference makes imposible for the electrons to flow anymore, so the function of the salty bridge is not only to close the circuit (a simple wire could do that) but to enable the current to flow.
Aim:
To create an electric circuit using salt bridges and redox reactions. the redox couples will be conected with wires to a multimeter which will show us the voltage or the current of the circuit.
Materials:
- Multimeter
- Black and red wires (like the ones in the picture)
- Copper
- Copper sulphate (CuSO4)
- Tin
- Tin nitrate Sn(NO3)2
- 2x beakers
- Cotton
- Salty water
- Water
- Curved cristal tube
Procedure:
- Take the curved tube and fill 1/4 of it with salty water.
- Fill it to the end with normal water and put cotton on it's endings so that water doesn't fall.
- Fill one of the beakers with copper sulphate and another one with the redox couple of tin.
- Connect one of the endings of the wires to the multimeter and with the other ending hold the copper wire.
- Repeat step 3 with the tin wire.
- Dip the copper and tin into their redox couple solution (be careful that the red or black wire don't touch the solution).
- Turn on the multimeter and look at it's screen (the given value should be of 0, ad we don't have a closed circuit)
- Place one end of the curved tube in one beaker and the other end in the remaining beaker.
- Now look at the value in the multimeter, it should be around 500
What did just happen?
We've just made a battery. The redox reaction created the perfect conditions for the electrons to flow; we can say redox couples are the passengers in the plane, as they pay electrons for the circuit to work, but why we needed to make a salt bridge (the curved tube) between the two beakers?: It is simple, we had the main components of a circuit, but it wasn't closed, this means that the electrons couldn't complete the circuit and therefore no current was made, but when we placed the salt bridge (which conducted electricity) we closed the circuit and enable the current to flow, we also equilibrated the two parts of the reduction.
We compared our results with the ones obtained by our classmates, and we found out that the current of a group was around 1000 in the multimeter, while our reached 520, how can this be possible?
It all has to do with the reduction potentials of the couples used, for example Cu+2/Cu has a reduction potential of +0.15, when we have a high reduction potential, we could say that the compound desires to be reduced (it is more possible for it to be reduced), while the Tin reduction potential Sn/Sn+2 is of -0.14, this means that it is more possible for it to be oxidized. our classmates worked with different redox couples, and we discovered that the one that got 1000 in the multimeter had a higher reduction potential difference in their couples, this means that the higher the difference in the reduction potential, the more current we are able to create.
The representation for our galvanic cell would be:
We compared our results with the ones obtained by our classmates, and we found out that the current of a group was around 1000 in the multimeter, while our reached 520, how can this be possible?
It all has to do with the reduction potentials of the couples used, for example Cu+2/Cu has a reduction potential of +0.15, when we have a high reduction potential, we could say that the compound desires to be reduced (it is more possible for it to be reduced), while the Tin reduction potential Sn/Sn+2 is of -0.14, this means that it is more possible for it to be oxidized. our classmates worked with different redox couples, and we discovered that the one that got 1000 in the multimeter had a higher reduction potential difference in their couples, this means that the higher the difference in the reduction potential, the more current we are able to create.
The representation for our galvanic cell would be:
Sn/Sn+2//Cu+2/Cu
Bibliography:
- Carnegie Mellon. (2012) Redox Couples. Recovered from http://chemed.chem.wisc.edu/chempaths/GenChem-Textbook/Redox-Couples-604.html
- All photos were taken by Juan Senín Vinuesa at the school lab
- Rey.L(2013) Redox reactions. Galvanic cells. Electrolysis. Recovered from https://mail-attachment.googleusercontent.com/attachment/u/0/?ui=2&ik=d06559dab7&view=att&th=13caea77a2dd1f22&attid=0.1&disp=inline&safe=1&zw&saduie=AG9B_P9mwM03WApaweJF_a6Bn2K6&sadet=1362941816416&sads=o0GFmHN5Aa_93ILfQjGmh0blPqg&sadssc=1
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