Ch. 11: Oxidation-Reduction Reactions (Complete) Flashcards
defn: oxidation-reduction (redox) reactions
reactions that involve the transfer of electrons from one chemical species to another
defn: the law of conservation of charge
electrical charge can be neither created nor destroyed
why can an isolated loss or gain of electrons never occur?
because of the law of conservation of charge
defn: redox reaction
an electron transfer that comes as a result of simultaneous oxidation (loss of electrons) and reduction (gain of electrons)
defn: oxidizing agent
defn: reducing agent
oxidizing agent: causes another atom in a redox reaction to undergo oxidation and is itself reduced
reducing agent: causes the other atom to be reduced and is itself oxidized
redox reaction mnemonic:
LEO the lion says GER: Loss of Electrons is Oxidation, Gain of Electrons is Reduction
OIL RIG is a mnemonic for the SAME
Oxidation Is Loss of electrons, Reduction Is Gain of electrons
what do almost all oxidizing agents contain?
oxygen or another strongly electronegative element (such as a halogen)
what do reducing agents contain?
metal ions or hydrides (H-)
True or False: Sometimes texts will describe the compound as a whole as the oxidizing or reducing agent
True (CrO3, rather than Cr6+)
func: oxidation numbers
assigned to atoms in order to keep track of the redistribution of electrons during chemical reactions
what are the 8 oxidation number assignment rules?
the oxidation number . . .
- of a free element is zero
- for a monatomic ion is equal to the charge of the ion
- of each Group IA element in a compound is +1
- of each Group IIA element in a compound is +2
- of each Group VIIA element in a compounds is -1, except when combined with an element of higher electronegativity
- of hydrogen is usually +1; however, its oxidation number is -1 in compounds with less electronegative elements
- of oxygen is -2, in most compounds
- the sum of the oxidation numbers of all the atoms present in a neutral compound is zero. the sum of the oxidation numbers present in a polyatomic ion is equal to the charge of the ion.
what is convention for order of cation and anion in a compound?
Cation first, anion second
what is similar and different between oxidation number and formal charge?
both account for the perceived charge on an element, but they 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 in bonds, “awarding” one electron to each atom in the bond
where should you start when assigning oxidation numbers?
start with the known atoms, which are usually groups I and II, halides, and oxygen
do transition metals have one or more than one oxidation states? why?
transition metals can take on multiple oxidation states
when transition metals are oxidized or reduced, the absorption and emission of light from a metal is altered such that different frequencies are absorbed
changes of oxidation state in transition metals usually correspond to a color change
what two things must be balanced when balancing a redox reaction?
the net charge
the number of atoms
defn + aka: half-reaction method
aka: ion-electron method
the equation is separated into two half-reactions, the oxidation part and the reduction part
each half-reaction is balanced separately, and they are then added to give a balanced overall reaction
defn: complete ionic equation
we split the various species into all of the ions present
defn: spectator ions
species that are present on both sides of the equation in the same form, are chemically inert within the reaction
they do not take part in the overall reaction but simply remain in the solution unchanged
defn: net ionic equation
shows only the species that actually participate in the reaction (no spectator ions)
what should you do with aqueous compounds, solid salts when writing net ionic equations?
aqueous compounds: split into their constituent ions
solid salts: keep together as a single entity
defn: combination reaction
two or more species come together to form a product
defn: decomposition reaction
one product breaks down into two or more species
defn: combustion reactions
a fuel (usually a hydrocarbon) is mixed with an oxidant (usually oxygen), forming carbon dioxide and water
defn + aka: double-displacement reactions
aka: metathesis reactions
involve the switching of counterions
why are double-displacement reactions not usually redox reactions?
because all ions generally retain their oxidation state
in double-displacement reactions where both reactants and both products are aqueous, is there a net ionic reaction? why or why not?
no, because all of the ions appear on both sides of the reaction
defn + aka + use: disproportionation
aka: dismutation
a specific type of redox reaction in which an element undergoes both oxidation and reduction in producing its products
used by many biological enzymes
what is the main difference between acid-base titrations and redox titrations?
acid-base titrations follow the movement of protons
redox titrations follow the transfer of charge (as electrons) to reach the equivalence point
what are two unique aspects of the indicators that redox titrations use?
they change color at a particular voltage (emf) value
they have different colors in their oxidized and reduced forms
defn + func: potentiometric titration
a form of redox titration where no indicator is used
instead, the electrical potential difference (voltage) is measured using a voltmeter
as a redox titration progresses, its voltage changes
defn + what does it rely on + process: iodimetric titration
a prototypical redox titration which involves the use of starch indicators to identify iodine complexes
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 endpoint of the titration, a colorless solution develops
what is potentiometric titration analogous to in acid-base titration?
acid-base titration with a pH meter instead of a color indicator
