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Chem 220 - Analytical Chemistry > Electrochemistry > Flashcards

Electrochemistry Flashcards

1
Q

define oxidation

A

a loss of electrons to an oxidizing agent

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2
Q

define reduction

A

a gain of electrons from a reducing agent

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3
Q

define oxidation numbers

A

indicates the number of electron lost, gained or shared from chemical bonds

oxidation: increase in oxidation number
reduction: decrease in oxidation number

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4
Q

what are the 6 rules for determining an oxidation number?

A
  1. free element is 0 (He, Cl2)
  2. Monatomic ion has an ON that is equal to the charge of the ion (NaCl)
  3. sum of all ON in neutral compound is 0
  4. ON for H is usually 1+, except when in compounds with less electronegative elements (NaH)
  5. ON for O is usually -2, except in peroxides then it is -1 (H2O2)
  6. sum of ON in a polyatomic ion is equal to the charge of the ion
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5
Q

what are the steps for balancing half reactions?

A
  1. first balance the atoms with coefficients
  2. then balance the charge by adding electrons
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6
Q

what are the steps to balance half reaction under acidic conditions?

A
  1. identify what atom is being oxi or red
  2. balance the atom that isn’t O or H first
  3. add H20 to balance oxygens
  4. add H+ to balance hydrogens
  5. add electrons to balance charges
  6. check everything again
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7
Q

what are the steps to balance half reaction under basic conditions?

A
  1. identify what atom is being oxi or red
  2. balance the atom that isn’t O or H first
  3. add H20 to balance oxygens
  4. add H+ to balance hydrogens
  5. neutralize any remaining H+ ions by adding the same amount of OH- ions to both sides of rxn
  6. react the H+ with OH- to form H2O molecules
  7. ADjust H20 coefficients on both sides (cancel out)
  8. check everything again
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8
Q

define galvanic cell

A
  • chemical reaction spontaneously occurs to rpoduce energy
  • anode is negative
  • cathode is positive

galvanic, anode and negative

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9
Q

define electrolytic cell

A
  • electricql energergy is used to force a non-spontanous chemical reaction to occur.
  • forced to go in the opposite direction of the galvanic
  • anode is positive
  • cathode is negative
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10
Q

define anode and cathode

A

anode: where the oxidation occurs
cathod: where the reduction occurs

an ox and red cat
anode oxidation and reduction cathode

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11
Q

define electrical potential

A

tendecny of the ions to give off or take on electron

the larger the potential, the greater the tendency for the reaction to occur

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12
Q

define SHE

A

standard hydrogen electrode
- potential difference between SHE and other half reaction have been measured using galvanic cells (table numbers)
- on a table, everything is written in terms of reduction, if you want to switch to oxidation, flip the sign on the voltage
- if you need to multiple a reaction to get electrons to cancel, DO NOT multiple the voltage, you can only change the sign if flipping around the reactionw

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13
Q

define cell bridge

A
  • A salt bridge is a device used in an electrochemical cell for connecting its oxidation and reduction half cells wherein a weak electrolyte is used.
  • a salt bridge is a junction that connects the anodic and cathodic compartments in a cell or electrolytic solution.
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14
Q

how do you properly do cell notation?

A
  • written in terms of anode and the cathode half cell
  • reactants followed by products
  • the notation reflects the direction of electron flow in the cell, spectator ions are not included
  • single line indicates species in different phase but still in contact
  • double line indicate a salt bridge separating the two half cells
  • phase of the species must be included
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15
Q

define potentiometric

A
  • this is an analysis consisting of measuring a solutions potential when little or no current is flowing, and relating it to its concentrations
  • use the Nerst equation
  • standard potentials are relating to the concentration of both reduced and oxidized forms of the cells
  • Q value does not include pure liquids, solids, or solvent
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16
Q

define reference electrode

A
  • to determine the potential of the unknown electrode
  • meant to provide a stable, reproducible voltage to which the working electrode may be referenced
  • it is independent of concentration of any other ions in solution
  • should maintain a constant potential in the presence of small current
  • most coom are calomel and silver/silver chloride
17
Q

define the calomel electrode

A
  • saturated calomel electrode (SCE)
  • consisting of small amounts of mercury mixed with some calomel
  • has platinum wire immersed in paste to make contact with a small mercury pool that was created
  • allows electrical contact between solutions inside and outside of electrode without physical mixing
18
Q

define the silver/silver-chloride electrode

A
  • reference electrode
  • paste of AgCl that is put in contact with solution of KCl and AgCl
  • porous plus at base of electrode allows contact between the solutions in and out of electrode without mixing
19
Q

define indicator electrodes

A
  • when one half-cell is comprised of the test solution and an electrode whose potential is determine by analyte we wish to measure
  • other half is reference electrode
  • any change in the potential of the indicator electrode will be reflected by an equal change in the cell voltage
  • only look for 1 ion
20
Q

defien ion-selective electrodes

A
  • they have a high degree of selectivity
  • only responding to 1 species in a solution
  • specific ion will cross a membrane creating a charge imbalance
  • potential difference across membrane is related to the difference in concentration fo the specific ion on either side of the membrane

image on page 26 of notes

21
Q

hwo do you measure pH with a glass electrode?

A

you use a thin glass membrane that is response to changes in H+ ion activity. when the ions build up across the glass membrane, its create a potential difference

22
Q

define coulometry

A
  • analytical method for measuring an unknown concentration of an analyte in solution by completely converitng the analye from one oxidation state to another
  • the amount of analyte is determined from the charge required to complete the reaction
  • direct: analyte reacts directly at one of the electrodes
  • indirect: an intermediate reagent is generated to react with analyte
  • lost of advantages but old technique that isn’t commonly used
23
Q

define electrodeposition

A
  • electric current to deposit a solid on an electrode from a solution
  • used to either oxidize or reduce analyte
  • amount of analyte is determined from the change in mass of the electrode

Chem 220 - Analytical Chemistry (10 decks)

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