General Chemistry- Oxidation Reduction Reactions Flashcards
What are the enzymes that catalyze oxidations called?
Dehydrogenases
What are oxidation-reduction reactions?
Reactions that involved the transfer of electrons from one chemical species to another
What is the Law of conservation of charge?
Electrical charge can be neither created nor destroyed
What is oxidation?
Loss of electrons
What is reduction
Gain of electrons
According to the Law of conservation of charge, what must occur at the same time?
Oxidation and reduction
What is an oxidizing agent?
Causes another atom in a redox reaction to undergo oxidation and itself oxidation
What’s a reducing agent?
causes the other atom to be reduced and itself oxidized
What is important to note for oxidizing agents? Reducing agents?
Almost all oxidizing agents contain oxygen or another strongly electronegative element (such as a halogen)
Reducing agents often contain metal ions or hydrides (H-)
What are the common oxidizing agents?
O2
H2O2
F2, Cl2, Br2, I2 (halogens)
H2SO4
HNO3
NaClO
KMnO4
CrO3, Na2, Cr2, O7 (seen in organic chemistry)
Pyridinium chlorochromate (PCC) (seen in organic chemistry)
NAD+, FADH (Biochemical reagents that act as energy carriers in biochemistry)
What are the common reducing agents?
CO C B2H6 Sn 2+ and other pure metals Hydrazine (seen in organic chemistry) Zn(Hg) (seen in organic chemistry Lindlar's catalyst (seen in organic chemistry) NaBH4 (seen in organic chemistry) LiAlH4 (seen in organic chemistry) NADH, FADH (Biochemistry)
What oxidizing agents are common in organic chemistry?
CrO3, Na2, Cr2, O7 Pyridinium chlorochromate (PCC)
What oxidizing agents are common in biochemistry?
NAD+, FADH (Biochemical reagents that act as energy carriers in biochemistry)
What reducing agents are common in organic chemistry?
Hydrazine (seen in organic chemistry) Zn(Hg) (seen in organic chemistry Lindlar's catalyst (seen in organic chemistry) NaBH4 (seen in organic chemistry) LiAlH4 (seen in organic chemistry)
What reducing agents are common in biochemistry?
NADH, FADH (Biochemistry)
What is important to note, for biochemical redox reagents such as NAD+
They tend to act as both oxidizing and recuding agents at different times during metabolic pathways. As such, they act as mediators of energy transfer during many metabolic processes.
Technically, the term oxidizing or reducing agent applies to what?
The terms are applied specifically to the atom that loses or gains electrons. However, many science texts will describe the compound as a whole (CrO3 rather than Cr6+) as the oxidizing or reducing agent.
Why are oxidation numbers assigned to atoms?
To keep track of the redistribution of electrons during chemical reaction. 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 are the rules to assign an oxidation number to a compound?
- The oxidation number of a free element is zero.
- The oxidation number for a monatomic ion is equal to the charge of the ion.
- The oxidation number of each group IA element in a compound is +1
- The oxidation number of each group IIA element in a compound is +2
- The oxidation number of each Group VIIA element in a compound is -1, except when combined with an element of higher electronegativity.
- The oxidation number of hydrgen is usually +1; however, its oxidation number is -1 in compounds with less electronegative elements (groups IA and IIA)
- In most compounds, the oxidation number of oxygen is -2. The two exceptions are peroxides, for which it is -1 and compounds with more electronegative elements, which would make it +2
- The sum of the oxidation number of all the atoms present in a neutral compound is zero. The sum of the oxidation numbers of the atoms present in a polyatomic ion is equal to the charge of the ion.
Oxidation number is often confused with what? Why?
Formal Charge, because both account for the perceived charge on an element, but do so in different ways.
What is the difference between formal charge and oxidation number?
Oxidation number assumes unequal division of electrons in bonds, “awarding” the electrons to the more electronegative element.
Formal charge, assumes equal division of electrons in bonds.
When assigning oxidation numbers, where should you start?
Start with the known atoms (usually Group I and II, halides and oxygen) Use this information to determine the oxidation states of the other atoms.
Why would you want to assign axidation numbers to the reactants and products of an equation?
One can determine how many moles of each species are required for conservation of charge and mass, which is necessary to balance the equation.
To balance a redox reaction, what must be equal on both sides?
The net charge and the number of atoms
What is the most common method for balancing a redox equation?
half-reaction method.
What is another name for the half-reaction method?
ion-electron method
How does the half-reaction method work?
The equation is separated into two half-reactions–the oxidation part and the reduction part. Each half-reaction is balanced separately, and the are then added to give a balanced overall reaction.
What is the complete ionic equation?
If we split the various species into all of the ions present
What are spectator ions?
Atoms not taking part in the overall reaction, but simply remaining in the solution unchanged
What is the net ionic equation?
Shows only the species that actually participate in the reaction.
In a net ionic equation, what ions should be kept together?
Solid salts
What are combination reactions?
Two or more species come together to form a product
What is a decomposition reaction?
One product breaks down into two or more species
Example: (NH4)2Cr2O7 (aq) –>N2 (g) Cr2O3 (s) + 4 H2O (g)
What is a combustion reaction?
A fuel (usually hydrocarbon) is mixed with an oxidant (usually oxygen) forming a carbon dioxide and water.
What are double-displacement or metathesis reactions?
Involve the switching of counter-ions. Because all ions generally retain their oxidation state, these are usually not oxidation-reduction reactions.
AgNO3 (aq) + HCl (aq) –> HNO3 (aq) + AgCl (s)
What are disproportionation or dismutation reactions?
A specific type of redox reaction in which an element undergoes both oxidation and reduction in producing its products. Many biological enzymes utilize a disproportionation mechanism
What is an example of a disproportionation or dismutation reaction?
the catalysis of peroxides by catalase, an enzyme found in peroxisomes. The activity of catalase can be seen when disinfecting a wound with hydrogen peroxide. 2 H2O2 (aq) -catalase-> 2 H2O (l) + O2
In the reaction 2 H2O2 (aq) -catalase-> 2 H2O (l) + O2, what are the different oxidation states of oxygen?
Each oxygen has an oxidation state of -1 (the peroxide ion has a charge of -2 overall). In water, oxygen has an oxidation state of -2, and in molecular oxygen, it has an oxidation state of 0. The oxygen is both reduced and oxidized.
Other than oxygen, what is another disproportionation mechanism?
The enzyme superoxide dismutase.
What does the enzyme superoxide dismutase do?
Catalyzes dismutation and frees radicals in the reaction.
Biochemical disproportionation reaction– and redox reaction in biological systems in general– are usually accomplished by what?
enzymes
Enzymes usually have what in their active sites, that act as what?
Metals such as Cu and Zn in active sites
Act as reducing agents
In enzymes, the atoms are stabilized in position by what?
Histidine residues
What is the difference between acid-base titration and redox titration?
Acid-base follow movement of protons
Redox follow the transfer of charge to reach equivalence point.
What indicators are used for redox titration?
Indicators that change color at a particular voltage (emf) value
What are the common indicators for redox titration?
Bipyridine metal complexes (Voltage of color change: +1V, Oxidized form (colorless (Ru), cyan (Fe)), Reduced form (Yellow (Ru), Red (Fe))
Diphenylamine (Voltage of color change: +0.76V, Oxidized form (Violet), Reduced form (Colorless)
Safranin (voltage of color change: +0.24/-0.29, Oxidized form (Red-violet), Reduced form (colorless).
What indicator is used to identify iodine complexes in redox titration?
Starch
What is the specific name of the redox titration that involves the identification of iodine complexes? Why
Iodimetric titration because it relies on the titration of free iodine radicals.
How is the presence of iodine determined in a iodimetric titration?
A dark solution in the presence of starch, and at the endpoint a colorless solution
What is potentiometric titration?
A form of redox titration where no indicator is used. Instead, the electrical potential difference (voltage) is measured using a voltmeter. As redox titration progresses, its voltage changes, this is analogous to following an acid-base titration with a pH meter instead of a color indicator.
