Chapter 11: Oxidation-Reduction Reactions Flashcards
What is a redox reaction?
Redox is short for oxidation-reduction reaction.
Redox reactions are reactions that involves transfer of electrons from one chemical species to another.
What is a mnemonic to use for redox reactions?
LEO the lion goes GER: Loss of Electrons is Oxidation, Gain of Electrons is Oxidized.
LEORA says GEROA: loss of electrons is oxidation (reducing agent), gain of electrons is reduction (oxidizing agent).
What is oxidation? What is reduction?
What is a reducing agent? Oxidizing agent?
Leora says geroa
Oxidation is loss of electrons, and is the reducing agent.
Reduction is gain of electrons, and is the oxidizing agent.
An oxidizing agent causes another atom in a redox reaction to undergo oxidation and itself reduced.
A reducing agent causes another atom in a redox reaction to be reduced and is itself oxidized.
What is a common note of almost all oxidizing agents? Reducing agents?
Almost all oxidizing agents contain oxygen or another strongly electronegative element (such as a halogen).
Almost all reducing agents contain metal ions or hydrides (H-).
Common oxidizing and reducing agents found on the MCAT
Before you perfect this card, you need to identify if acids are good oxidizing or reducing agents (give examples), remember a biologically important oxidizer/reducer (which one is which).
An oxidizing agent is a substance that causes another substance to oxidize by accepting electrons from it, essentially “taking” electrons away from the other substance, which means the oxidizing agent itself gets reduced in the process; think of it as the “electron acceptor” in a chemical reaction.
A reducing agent gets oxidized, lose electrons.
NAD+ tends to act as both an oxidizing agent and reducing agent at different times depending on the biological demand in metabolic pathways. They are known as mediators of energy transfer during metabolic processes. The purpose of this card for now is to look at the image and talk about it regarding energy transfer and redox.
Does oxidizing agent gain or lose electrons? Does reducing agent gain or lose electrons?
On a technical level, the term oxidizing agent or reducing agent is applied specifically to the atom that gains or loses electrons, respectively.
The oxidizing agent gains electrons, the reducing agent loses electrons.
However, many science texts will describe the compound as a whole as the oxidizing or reducing agent (for example CrO3 rather than Cr+6).
What are oxidation numbers used for?
Oxidation numbers are assigned to atoms in order to keep track of the redirection of electrons during chemical reactions.
Based on the oxidation numbers of the reactants and products, it is possible to determine how many electrons are gained or lost by each atom.
What is a handy way that DJ remembers reduced and oxidized in terms of energy of molecules?
DJ thinks about it like this:
Relate metals and nonmetals and their typical ion formation with oxidation and reduction.
Metals form cations, nonmetals form anions.
To form a cation, metals like to get oxidized (lose electrons) and act as good reducing agents.
To form anions, non metals like to get reduced (gain electrons) and act as good oxidizing agents.
What is the conventional formula for writing cations and anions in a compound (first and last)?
The conventions of formula writing put cations (+) first and anions (-) second (like NaOH —> Na+ and OH-).
Use the way a compound is written on the MCAT along with the periodic table to determine oxidation states.
The oxidation number of an atom in a compound is assigned according to a set of rules. What are these 8 rules?
Are strong bases considered good oxidizing or reducing agents?
Are strong acids considered good oxidizing agents or reducing agents?
Remember Lewis acid base definitions.
Strong bases are good reducing agents because they readily donate electrons (lose electrons and therefor become oxidized). Strong bases can generally be considered good reducing agents because, according to the Lewis acid-base theory, a base acts as an electron donor, which is the key characteristic of a reducing agent; meaning a strong base has a higher tendency to donate electrons, making it a better reducing agent.
Strong acids are good oxidizing agents as they readily accept electrons (gain electrons and therefor become reduced)
Acids generally act as electron acceptors in a reaction, meaning they tend to get reduced themselves, making them oxidizing agents.
Example image of the Lewis structure of CO2 regarding the oxidation number of oxygen and carbon. What is the oxidation number of carbon and oxygen in carbon dioxide?
The book recommends starting with known atoms oxidation numbers. What does this mean?
When is signing oxidation numbers, start with the known atoms (group IA and IIA) and use this information to determine the oxidation states the other atoms.
What is the difference between formal charge and oxidation number?
Both formal charge and oxidation number account for the perceived charge on an element, but do so in different ways.
Oxidation number assumes unequal division of electrons in bonds, awarding the electrons to the more electronegative element.
Formal charge assumes equal division of electrons and bonds, awarding one electron to each in the bond.
In reality, the distribution of electron density lies somewhere between these two extremes.
Example oxidation number of atoms in molecules in a reaction page 413
What is the half reaction method for balancing redox reactions?
The half reaction method, aka ion-electron method, is a common way to balance redox reactions in which the equation is separated into two half reactions - the oxidation part and the reduction part. Each half reaction is balanced separately and then are added to give a balanced overall reaction.
Example half reaction method for balancing redox reactions page 414
Concept check 1.1 redox reactions page 415 question 1
Concept check 1.1 redox reactions page 415 question 2
Concept check 1.1 redox reactions page 415 question 3
What are the steps for using the half reaction method for balancing redox reactions?
Good conversation for clarification. When using the half-reaction method to balance a redox reaction, you always put electrons on the product side (right side) for the oxidation half-reaction and on the reactant side (left side) for the reduction half-reaction; essentially, electrons are added to the side where the species is gaining electrons (reduction) and removed from the side where it is losing electrons (oxidation).
This could make intuitive sense. If the species is losing electrons, you will find electrons on the reactant side. If the species is gaining electrons, you will find electrons on the products side.
STEP ONE IN THIS PROCESS IS TO IDENTIFY THE REDOX SPECIES.
Write the complete ionic equation for the following reaction. Then write the net ionic equation.
What is the difference between complete ionic reaction and net ionic reaction? What ions are considered in the net ionic equation?
Complete ionic reaction shows all of the various species split into all of the ions present.
For the net ionic equation, aqueous compounds should be split into their constituent ions. Solid salts should be kept together as a single entity.
The net ionic equation includes only the species that actually participate in the reaction (it is the reaction minus the spectator ions).
What is a spectator ion?
A spectator ion is an ion that is not involved in the redox reaction and therefor not found in the net ionic equation.
Look for compounds such as polyatomic anions that retain their charge before and after the reaction. These are usually spectator ions and will not be found in the net ionic equation.
What is a combination reaction? Give the relevant half reactions and net ionic equation for the following reaction:
A combination reaction is a reaction where two or more species come together to form a product.
Recall how to know where to put electrons in the half reactions. Which one gains electrons? Which one loses electrons?
What is a decomposition reaction? Write the relevant half reactions and net ionic equations for:
A decomposition reaction is a reaction where one product breaks down into two or more species.
What is a combustion reaction? Write the relevant half reactions and net ionic equation for the following:
Combustion reactions are reactions that involve a fuel (usually hydrocarbons) mixing with and oxidant (usually oxygen), forming CO2 and water.
Note that the net ionic equating is the same as the balanced equation because no spectator ions or aqueous species.
What is a double displacement (metathesis) reaction? Are these generally considered redox reactions? Why or why not? Provide example using the following:
Double displacement or metathesis reactions involve the switching of counter ions. Because all ions generally retain their oxidation state, these are not usually oxidation reduction reactions.
Because all species retain the same oxidation number, the example is not considered oxidation reduction.
Is there a net ionic reaction equation for double displacement reaction where both reactants and products are aqueous? Are they considered redox reactions? Why or why not? Use the following as an example:
The example is not a redox reaction, there is no net ionic reaction.
What is a disproportionation (dismutation) reaction? Use the following example to discuss disproportionation reactions. Catalase and superoxide dismutase, what are? What are common metals found in enzymes active sites that act as reducing agents?
disproportionation, or dismutation, reactions are reactions where an element undergoes both oxidation and reduction in producing its products.
Many biological enzymes utilize dismutation reactions, such as catalase and superoxide dismutase as shown in the image. Biochemical disproportionation reaction, and redox rxns in biological systems in general, are usually accomplished by enzymes.
Cu and Zn are typically found in enzymatic active sites and utilized for these reactions.
Concept check net ionic reactions 11.2 page 421 question 1
There are a couple things to recognize here.
The first equation is more simple than it looked to begin with. Need to recognize NO3 (nitrate) as a polyatomic ion with charge -1. CuCl is a solid and therefor status together in the complete and net ionic equation. Na and NO3 are spectator ion, and the charges and masses are balanced as soon as you eliminate the spectators from the reaction.
Second reaction. The reaction is not balanced. CHECK TO SEE IF ANY AND ALL OF THE REACTIONS GIVEN ON THE MCAT ARE BALANCED. This became simple after balancing. Notice what was done with the Cl in AlCl when making the complete ionic equation. Eliminate spectator ions and charges were balanced already.
Concept check 11.2 net ionic reactions page 421 question 2
About these reactions. We need to determine the oxidation state of all the constituent atoms. We got stuck on the first one by staying with the oxidation state of the polyatomic ion (ClO3-) and we needed to know the oxidation state of Cl and O to determine what is being oxidized and or reduced.
The second reaction. We get to the point of needing the oxidation state of sulfur in S2O3 2-. Set up an algebraic equation to solve for oxidation state x of sulfur. Bam.
Concept check 11.2 net ionic equations page 421 question 3
Dimensional analysis is critical for this question. Also notice that the question gives us grams of sample and that is not needed for this question. The molarity (mol/L concentration) was given and that’s what we need to calculate the reaction.
Also, I got stuck on:
(0.7)(32.6)(207.2)/1000.
I realized that this was the same as (0.7)(32/10)(207/100)
It then simplified to (0.7)(3)(2)
And then to 42/10
Example of a prototypical redox reaction involving the use of starch indicators to identifying iodine complexes. This reaction is called an iodometric titration because it relies on the titration of free iodine radicals. The presence of iodine is initially determined by a dark solution in the presence of starch, and at the end point of the titration, a colorless solution develops. A common general chemistry laboratory experiment involves the standardization of a thiosulfate solution using iodometry.
Example page 420.
Ok so this complex of an analysis is beyond the scope. However, it has all the things involved with redox and net ionic equations with complex stoichiometry at the end.
Mastery redox reactions chapter 11 page 406 question 1
Mastery redox reactions chapter 11 page 406 question 2
Mastery redox reactions chapter 11 page 406 question 3
Mastery redox reactions chapter 11 page 406 question 4
Mastery redox reactions chapter 11 page 406 question 5
This is a fun question. Needs me to be able to identify the element by its electron configuration. Furthermore, knowing trends of ionization energy on the periodic table.
Book answer: A strong oxidizing agent will be easily reduced, meaning that it will have a tendency to gain electrons. Atoms usually gain electrons if they are one or two electrons away from filling up their valence shell. A has a full 4s orbital, B has a stable half full 3d orbital, she has only a single electron in its outer shell (which is more likely lost upon ionization). D would fill up its 4p orbital by gaining one electron, so it is easily reduced.
DJ answer in image:
Mastery redox reactions chapter 11 page 406 question 6
A net ionic equation represents each of the aqueous ions comprising the reactants and products as individual ions, instead of combining them as formula units, therefore A is not a net ionic reaction.
The term net means that the correct answer does not include any spectator ions (ions that do not participate in the reaction). This eliminates B and C.
My thoughts in the image.
Mastery redox reactions chapter 11 page 406 question 7
What you were shown as a net ionic equation. If 2 moles FeSCN are created, two moles of Fe 3+ must be used because the mole ratio is one to one. Figure out the formula of iron sulfate using the charges given in the net ionic equation Fe2(SO4)3.
This is the confusing part. We need a molar ratio that tells us how many moles of iron sulfate are needed to make two moles of iron thiocyanate?
Thoughts were making the equation or as follows: if I want two moles of iron thiocyanate, I need to work backwards from iron thiocyanate to Fe 3+ and then from Fe 3+ to moles iron sulfate.
Aha moment. We need to consider the normality of Fe2(SO4)3. One mole of that contains two moles of Iron. The question is asking about producing 2 moles FeCN 2+.
The correct answer is C.
Mastery redox reactions chapter 11 page 406 question 7
When assigning oxidation numbers, one starts with the elements of known oxidation state first, and determines the oxidation state of the other elements by deduction.
Argon, answer A, is a noble gas and will always have an oxidation state of zero.
Fluorine, answer B, will have an oxidation station state of zero by itself or negative one in a compound.
Strontium, answer C, is a group IIA element and will have an oxygen station state of zero by itself or +2 in a compound.
Iridium, answer D, like most transition metals can have various oxidation states ranging from -3 to +8. Therefore one would have to determine the oxidation states of the other atoms in an iridium containing compound to determine iridium oxidation number.
The correct answer is D.
Mastery redox reactions chapter 11 page 406 question 9
Mastery redox reactions chapter 11 page 406 question 10
Answer page 427 if this is confusing. Was not confusing when I made this card.
Mastery redox reactions chapter 11 page 406 question 11
You could simply look at this question telling you that the acidity of the metal increases as the oxidation state increases. The oxidation state could be thought of as how many bonds it has with oxygen. The more bonds with oxygen, the more oxidized it is. Option B has the most bonds with oxygen. The correct answer is option B.
Image does the calculations:
Mastery redox reactions chapter 11 page 407 question 12
Mastery redox reactions chapter 11 page 407 question 13
Potentiometry refers to carrying out an oxidation-reduction titration with a volt meter present to get precise readings of the reactions electromotive force (emf) to determine the endpoint. This is analogous to using a pH meter in an acid base titration because it uses technology to get precise readings for plotting a titration curve.
Indicators, as in A and B, can be used in both acid base and redox titration, but provide a qualitative analysis of the titration.
Oxidizing and reducing agents are used in redox titrations, not acid base titration, eliminating D.
Mastery redox reactions chapter 11 page 406 question 14
This question is asking you to balance a net ionic equation. First you need to balance the elements. Then you need to balance charges. Then you need an equal amount of electrons on either side.
Then you simply add all the stoichiometric coefficients.
Mastery redox reactions chapter 11 page 406 question 15
This is a simple stoichiometry question, however the reaction equation provided is not balanced and we must have a balanced equation before we can get the mole ratio.
In order to get the balanced reaction, I first took the complete ionic equation, then removed the spectator ions (sodium), then took the half reactions, balanced them first for moles and then charge (there are examples to refer to in this deck if that is not familiar enough), added the half reactions, then placed spectator ions back into the reaction. I could get the mole ratio after the reaction was balanced.
