CHEM 191 Lecture 16 Flashcards
loss of electrons is ___
oxidation
gain of electrons is _____
reduction
when atoms exist as elements, they have an oxidation number of
0 - e.g. Na, Cl2, C
the oxidation of monatomic (one atom) ions is
the same as the charge of the ion - e.g. Cu2+ has a change of 2+
hydrogen in compound has an oxidation number of
+1
oxygen in compounds has an oxidation number of
-2 - except in hydrogen peroxide where is has an oxidation number of -1
the sum of the oxidation numbers of atoms in a molecule is
zero - e.g. the sum of the oxidation numbers for the atoms in H2SO4 is zero
the sum of oxidation numbers of atoms in a polyatomic ion is
equal to the charge on the ion - e.g. the NH4+, the oxidation numbers for the atoms add to +1
a positive change of an oxidation number indicates a _____ of electrons. negative change indicates a _____ of electrons
loss - gain
in the reaction 2Na + Cl2 —> 2Na+ + Cl- what are the oxidising and reducing agents
the oxidising agent is Cl2
the reducing agent is Na
if electron transfer occurs then a driving force or potential difference must exist. units of potential difference are
JC-1
energy per unit charge
reaction potentials can be thought of as energy change when a substance _____ electrons. the _____ change in energy wins.
gains - biggest
in a reaction the substance with the highest potential energy (highest reduction potential) will _____ the electrons most. while the substance with the lowest potential will _____ electrons
attract - lose
the overall potential difference for the reaction can be found using
E^0 reaction = E^0 reduction process - E^0 oxidation process
what are galvanic cells used for
in order to determine the magnitude of the potential difference
what is the function of the salt bridge in a galvanic cell
it carries ions from one half of the reaction to the other
the cathode is always where you get _____. the anode is always where you get _____.
reduction - oxidation
what does E0cell measure
the difference between how much each side wants to gain electrons
what is the equation for E0cell
E0cell = E0RHS - E0LHS
what are E0RHS and E0LHS
the standard reduction potentials for each of the half cells
the sign of the E0cell indicates…
which electrode has the reduction process. a positive value indicates reduction is occurring on the RHS electrode. a negative value indicates reduction is occurring on the LHS electrode
what is the SHE used for
it is a reference electrode that is used to find the sign and magnitude of individual reduction potentials. we define the alf cell to have a standard reduction potential of zero
