Redox Flashcards

Electrochemistry is the study of electron transfers in chemical reactions. It is referred to as redox as it is made up of reduction and oxidation.

• Reduction is when is when an itom/ion gains electron(s) e.g. Cu2+ (aq) -> CU (s). In a reduction half reaction electrons are written on the reactants (left).
• Reducing agents are the ingredients added in chemical rxns that causes the oxidation of a metal compound into a pure metal. They are usually nonmetal anions and metal solids.

• Oxidation is when a substance/ion loses electron(s). e.g. Cu(s) ->Cu2+ (aq). In an oxidation half rxn electrons are on the products (right) side.
• Oxidizing agents are the ingredients added to chemical rxns that reduces a metal to become oxidized (makes the metal into an ion). They are usually nonmetal diatomic elements and metal cations.

• 1.break the net ionic rxn into 2 half rxns without coefficients ( label one for reduction and one for oxidation)
• 2. balance the substances by added coeffixients
• 3. balance electrons. add them to the most positive side. both sides must have the same charge.

Since in a rxn where substances echange electrons one is always oxidized and one is always reduced they are called redox reactions. In a redox rxn the reducing agent is oxidized (donates e-) and the oxidizing (accepts e-) agent is reduced.

• A redox table is a list of reduction half reactions (there are also oxidization tables). In such a table half rxns are in a specific order; the strongests oxidizing agent (SOA) is at the top left of the table and the strongest reducing agent (SRA) is at the bottom right. Since electronegativity is the tendency of an atom to attract bonding e-, elements with high electroneg are stronger oxidizing agents while strong reducing agents have low electronegs. 
• If the OA is above the RA on the standard reduction table the rxn is spontanteous, if the RA is above the OA the rxn is non-spontaneous.

• 1. list all species mentioned in the question (remember soluble ionic cmpnds dissociate, molecular cmpnds don't, SA's ionize WA's don't, if u see the word acidic list H+(aq) if u see basic list OH-(aq) and all aqeuous solutions contain H2O(l).
• 2. Find OA's and RA's from species list.
• 3. find SOA by starting on the top left side of redox table and going down until you find one of your OA's, then write the reduction half rxn from left to right. Find SRA by starting on the bottom right side and going up until you find one of you RA's, then write your oxidation half rxn from left to write.
• 4. balance half rxns (make e- gained=e- lost)
• 5. Add the two half rxns to make a net ionic eqxn and determine spontaneity

• 1. list the species and come up with a balanced redox eqxn.
• 2. convert known information into moles
• 3. use mole ratio or swoop to convert known moles to unknown moles
• 4. convert unkown moles in the correct units

For titration the process is the same except for volume you use the average from all the titrations (exlude any values outside of ±0.2)

• Oxidation numbers are numbers used to keep track of how many e-'s are lost or gained by each atom in a redox rxn. they represent the oxidation state (real or apparent charge) of an atom/ion.
• Rules:
• 1. Pure elements #=0
• 2. Simple ion's # is equal to the ions charge
• 3. Alkali metals are always +1, akali earth metals are always +2
• 4. Oxygen's# in compounds is -2, unless in peroxides where it is -1
• 5. The # for Hydrogen is +1 unless in a metallic hydride where it is -1 (e.g NaH)
• 7. When nonmetals combine the atom with greater electroneg. has a # equal to its ion charge.
• 8. Sum of oxidation numbers=net charge on molecule

• 1. Without a redox table, first assign oxidation numbers (focus on the major species (ones that underwent redox)), then determine the number of e- transferred per each atom and whether a reduction or oxidation occured. Thirds find the lowest common multiple of electrons betweeen the oxidation and reduction. finally balance O's by adding H2O(l) and H's by adding H+ (aq).
• t
• 2. Half rxn method (in acid/base conditions). Start by assigning oxidation numebrs and splitting the rxn into 2 half rxns (one for oxidation one for reduction). Then balance your major species across both sides, then balance O's by adding water to the low side and then H's with H+ on the low side. Balance your charges by adding electrons and finally add the two half rxns together.

• THere are disproportionation rxns where a species is both the RA and OA. TO balance these rxns, write the substance that is being both oxidized and reduced twice, once in reduction and once with is oxidation.
• THen there are equations with more than two main actors, to balance these split them into 2 half rxns and balance like normal.
• Photosynthesis is a redox rxn becuase there is a movement of e-'s, the Carbon in CO2 gains 4 electrons while the oxygen in H2O loses 2 electrons.

• A voltaic cell is a device which spontaneously converts chemical e into electrical e thru a redox rxn. A simple voltaic cell consists of two electrodes in a conducting solution (electrolyte), the solution contains anions/cations. One electrode (half cell or half rxn) is an anode and the other is a cathode
• Their parts are:
• The two halfs are connected by a wire so e- can flow
• The salt bridge/porous cup also connects both to allow ions to flow between both cells 
• The electrodes are solid pieces of metal where the half rxns occur, these pieces must conduct
• The Cathode is the site of the reduction half rxn, it is located in the half cell with the SOA and it collects e- and itself - gaining mass
• The Anode is the site of the oxidation half rxn, located in the half cell with the SRA, it loses e- and itself - losing mass
• The anions are negative and flow towards the anode, the cations are pos. and flow towars the cathode

• A cell is one electrochemical rxn while a battery is multiple hooked together.
• 1. To label voltaic cells you first create a species list
• 2. using your reduction half rxn table label your SOAC (solid that is in the reduction half rxn) and your SRAA (solid in oxidation half rxn)
• 3. label the direction of electron flow (anode to cathode)
• 4. Label ion flow - anions go from cathode to anode across the salt bridge and cations go from anode to cathode
• 5. determine the voltage from you reduction half rxn table, in the SOA the sign on the voltage is the same and in the SRA the voltage sign is opposite, do not multiply this voltage like you do with your electrons. Then calculate your net voltage by adding the two.
• A positive voltage means a rxn is spontaneous while a neg. voltage means the rxn is non-spontaneous.

cell notation is how you describe a voltaic cell w/out drawing it. It's order is electode|electrolye||electrolyte|electrode. An inert electrode is an electrode (solid metal) that does not react. They are used when there is no metal that corresponds to the ion or when using gasses. This is when there is no solid metal in any of your half rxns for your voltaic cell. In this situation you add an inert electrode (C(s) in the half rxn, Pt(s) ot sometimes Ag(s)). You can only replace something in the cell if it is not the SOA or SRA.

THe differenece in energy between two points on a circuit per unit of charge. A strong RA and a strong OA paired together will have a high voltage a wra and woa will have a small voltage. THe units of voltage is volts (J/C or V). To calculate the voltage you use the formula ∆E= Er(SOA)-Er(SRA). Since the data booklet gives a reduction half rxn table the oxidaiton potential has the oppositee value. Since the data booklet half rxn table is centered around the hydrogen half cell (hence why it has 0.00v) all other given voltages are relative. Therefore to calculate voltage around a new reference you use the formula Voltage - "new reference" = new voltage. Remember net voltage never changes even if the reference does.

Cell stoich can be used to calculate moles of e-'s since they are included in half cell half rxns, by using the amount of current, time and Faradays constant. Faradays constant relates the amount of charge transferred to amound of electricity, F=9.65x10⁴ C/mole e-. This means one mole of e- has a charge of 9.65x10^4 C. We can use the formula n_e=It/F where ne is the number of moles of e-, I is the current in amps (A or C/s), t is time in seconds and F is the constant.

They are another kind of electrochemical cell, except they convert electric energy into chemical energy nonspontaneously (unlike voltaic cells which are the opposite). These rxns do not require a salt bridge as they are nonspontaneous and they use a power source instead of a voltimeter. Determining the half rxn is similar to how you do it with voltaic cells except this time the SRAA is above the SOAC on your table.

It is when Electrolysis occurs with solutions containing Cl-(aq), chloride is used as the SRA instead of water. In these situations water is the SRA but Cl- is used instead as they react preferentially. Names for these solutions are salt water, ocean water, brine, brackish, etc.

Molten means liquid, this means there is no water present in these cells, though molten ionic compounds still split up into ions like an aq cell meaning we still have electrolytes but their states are liquid. To create an electrolysis eqxn for this situation we list our species without water and use the SOAC and SRAA to make a net reaction.

Electroplating is the process of coating or plating a metal w/ another thru electrolysis. This is for decoration or corrosion prevention. Electrorefining is the process of purifying/refining a metal from alloy/ores thru electrolyis, copper is usually used. Remember that during electrolysis your cathode collects and anode away (anode loses).

When a cell is linked to another cell we can assume the number of electrons passing through one cell is the same as the other. We can use this to figure out the electrons in the anode and cathode by first figuring out the moles of the electrons for the half rxn with a given mass and then using that number to figure the mass change at the other electrode. Additonally if current and time are the same across multiple electrodes we can figure how much different materials gain and lose in comparison.

A dry cell is a sealed electric cell with semi-solid conductors. A primary battery cannot be recharged, a secondary battery can. A fuel cell is a cell where the fuel is continuosly added (hydrogen fuel).

• To prevent the corrosion of metals we can use a sacrificial anode which will oxidize instead. These are metals that are better SRA's so that the more valuable metal will not be used and these will be oxidized instead. For iron we most commonly use Mg(s), Al(s) and Zn(s) as they are affordable and safe (the others are either explosive (Na, Li and K), or poisonous (Cr)). 
• We can also paint metals so they are not exposed and therefore cannot rust, Galvanize them - coat them with zinc, or apply a current - the DC electricity applies electrons to the OA so the metal doesn't have to.