Standard Reduction Potentials - Online Tutor, Practice Problems & Exam Prep

Oxidation and reduction are chemical processes where oxidation refers to the loss of electrons, and reduction is the gain of electrons. The tendency for these reactions to occur can be measured using standard reduction potentials (E°), which are determined under standard conditions (25°C, 1 atmosphere, 1 M concentration, pH 7). A higher E° value indicates a greater likelihood of reduction. The standard hydrogen electrode (SHE), with an E° of zero, serves as a reference point. Elements with E° values above zero are strong oxidizing agents, as they readily gain electrons, whereas those with E° values below zero are strong reducing agents, more likely to lose electrons. This concept is crucial for understanding the electrochemical behavior of elements and compounds, predicting the direction of redox reactions, and identifying the role substances play as either oxidizing or reducing agents in chemical processes.

The Standard Reduction Potential

In this video, we're going to take a look at an old concept of oxidation and reduction, and now combine it with a new variable, our standard reduction potential. Here its variable is E0 or 0 and then red for reduction. Here it's a tendency of a species to gain electrons from another species, we're going to say.

Recall that reduction is the gain of electrons while oxidation is the loss of electrons. Ince it has this knot. Here we're going to see that standard reduction potentials values are measured at standard conditions. Standard conditions means our temperature is 25°C, our pressure is 1 atmosphere, our molarity or concentration is 1, and our pH is equal to 7.

We're going to say that the higher your standard reduction potential value, then the more likely reduction will occur. Now that we've compared our old concepts of oxidation reduction to our new concept of standard reduction potentials, let's take a look at comparing different elements and compounds and their given standard reduction potentials.

Comparing Standard Reduction Potentials

Here in this image we have different types of elements and they're given standard reduction potentials. So here we can see that they're represented as half reaction reduction, half reactions. And we know there are reductions because if we were to calculate the oxidation numbers, let's say for fluorine here it's in its neutral state, so it's zero, and now it has a charge of -1, so each fluorine is now -1. The oxidation number decreased, so we know that this represents a reduction.

Another helpful way to remember that these are reduction reactions is that the electrons are reactants. So electrons as reactants equals reduction, so R with R. Here we can see that our fluorine F₂ gas has the highest reduction potential and in this list we see that lithium has the smallest. Now we will also see that we have

2 H + aqueous + 2 e → H 2 gas

It has a standard reduction potential of 0. This kind of acts as our border and we can compare the strength of reduction potentials on whether they're above 0 or below 0.

Here we're going to say that this is our border. It also has its own unique name. It's called the SHE. Now that stands for standard hydrogen electrode. Now recall we said that the higher your standard reduction potential is, then the more likely reduction will occur. So here we see that F₂ has the highest standard reduction potential, so it wants to be reduced more than anything else. Now if you are a, if you're being reduced, what kind of agent would you be? Well, remember if you're being reduced, that means you're the oxidizing agent.

Here, we're going to say as we go up this group, the ability to be reduced increases and therefore the strength of being the oxidizing agent also increases because remember oxidizing agent is tied to reduction. If reduction is going up, being an oxidizing agent is also going up. Conversely, if you look the opposite way, we're saying if we go down the list, then our standard hydrogen or standard reduction potentials are getting smaller. If they're getting smaller, you're less likely to do reduction, you're more likely to do oxidation. And remember, if you're being oxidized, that means you're the reducing agent.

So we're going to say going down the list, you're going to say oxidation more likely. So your strength of being oxidized is increasing and therefore your strength of being reducing agent is increasing. OK. So here that's what we can say in terms of this chart. So going up the list, the numbers get bigger, so reduction is more likely and therefore you're a stronger oxidizing agent. Going down the list, your standard reduction potential gets smaller, so oxidation is more likely and therefore you are stronger reducing agent. So keep this in mind when looking at comparing the different types of standard reduction potentials of different elements.

Standard Reduction Potentials Example

Here it says determine which of the following will least likely donate an electron. So if we're talking about something donating an electron, that means that it itself is being oxidized. OK, so they're saying least likely to donate an electron means least likely to be oxidized. Causeway, remember how would I be able to donate an electron? I have to give it up. Oxidation means we're losing electrons. We're donating them to our other species.

So here we have H₂, BR₂, zinc 2 plus zinc ion, chloride and Li plus. So the one that's least likely to be oxidized means the one that is more likely to be reduced. So when we say the one that's most likely to be reduced, what does that really mean? Well, in relation to our reduction potential, it be the one with the largest E value, so one with our largest standard reduction potential.

When we take a look here, we have H₂, we know that that forms our boundary. So that's at 0 volts. We have BR₂ here, which is at 1.09 volts. We have zinc, which is related to this point, 76 volts. Chlorine is 1.36 volts. And then we have lithium which is way down on the bottom at -3.04 volts.

The one with the largest standard reduction potential, which means it's more likely to be reduced and least likely to be oxidized, would have to be CL₂. So here our answer would have to be option D. So option D CL₂ would be our final answer.

Rank the given metal ions in order of increasing strength as an oxidizing agent.

Pb²⁺ (-0.13 V), Mn²⁺ (-1.18 V), Cu²⁺ (+0.16 V), Co³⁺ (+1.82 V), Fe³⁺ (+0.77 V)

• A. Pb2+ < Cu2+ < Mn2+ < Co3+ < Fe3+
• B. Co3+ < Fe3+ < Cu2+ < Pb2+ < Mn2+
• C. Mn2+ < Pb2+ < Cu2+ < Fe3+ < Co3+
• D. Mn2+ < Pb2+ < Cu2+ < Co3+ < Fe3+

Determine which species can oxidize Br₂.

• A. Fe3+
• B. Ni2+
• C. H+
• D. F2

Here’s what students ask on this topic:

Which statement is true about standard reduction potentials?

Standard reduction potentials (SRPs) are values that reflect the tendency of a chemical species to gain electrons and thereby be reduced. A positive standard reduction potential indicates that a species is more likely to be reduced (gain electrons), and it is a stronger oxidizing agent. Conversely, a negative standard reduction potential suggests that the species is less likely to gain electrons and is a stronger reducing agent. These potentials are measured under standard conditions, which are 25 degrees Celsius, a 1 M concentration for each ion participating in the reaction, and a pressure of 1 atmosphere for any gases involved. SRPs are tabulated with reference to the standard hydrogen electrode (SHE), which is assigned a potential of 0 volts. By comparing the SRPs of different half-reactions, you can predict the direction of electron flow in a redox reaction and determine which species will be oxidized and which will be reduced.

Given the standard electrode reduction potentials, which reaction will occur spontaneously?

To determine if a reaction will occur spontaneously based on standard electrode potentials (also known as standard reduction potentials), you need to compare the potentials of the two half-reactions involved.

A spontaneous reaction in electrochemistry is one that has a positive cell potential, $E_{\mathrm{cell}}$. The cell potential is calculated using the formula:

$E_{\mathrm{cell}}=E_{\mathrm{cathode}}-E_{\mathrm{anode}}$

Here, $E_{\mathrm{cathode}}$ is the reduction potential of the cathode (where reduction occurs), and $E_{\mathrm{anode}}$ is the reduction potential of the anode (where oxidation occurs). However, since the anode is actually being oxidized, you need to reverse the sign of its standard reduction potential when you use it in the equation.

If the difference $(E_{\mathrm{cathode}}-E_{\mathrm{anode}})$ is positive, the reaction will proceed spontaneously. If it is negative, the reaction is non-spontaneous under standard conditions. Remember that standard conditions mean all solutes are at 1 M concentration, all gases are at 1 atm pressure, and the temperature is 298 K (25°C).

Which statements are true regarding standard reduction potentials? Which ones should be selected?

Standard reduction potentials (E°) are a measure of the tendency of a chemical species to be reduced, and are measured in volts. Here are some true statements about standard reduction potentials:

1. Standard reduction potentials are measured under standard conditions, which are 25°C, 1 M concentration for each ion participating in the reaction, a pressure of 1 atm for any gases involved, and a pure solid or liquid for each pure substance.
2. A positive standard reduction potential indicates that a species has a greater tendency to gain electrons and be reduced, while a negative value suggests it is less likely to gain electrons.
3. The more positive the reduction potential, the stronger the oxidizing agent. Conversely, the more negative the reduction potential, the stronger the reducing agent.
4. The standard hydrogen electrode (SHE) has a standard reduction potential of 0 volts by definition, and it serves as the reference electrode against which all other electrode potentials are measured.
5. Standard reduction potentials can be used to predict the direction of a redox reaction; a spontaneous reaction will have a positive cell potential when the potentials are combined.
6. When using standard reduction potentials to determine the feasibility of a reaction, the species with the higher reduction potential will be reduced, and the one with the lower reduction potential will be oxidized.