Unit 4

Question 1

Redox Reactions

Answer 1

reduction- oxidation

- when on or more electrons are transferred from one species to the other

Question 2

oxidation

Answer 2

loss of electrons, oxidation number increases

Question 3

reduction

Answer 3

a gain of electrons, oxidation number decreases

Question 4

half-reactions

Answer 4

they are like writing one element and the electrons it looses/gains

Question 5

e- is product

Answer 5

oxidation

Question 6

e- is reactant

Answer 6

reduction

Question 7

oxidizing agent

Answer 7

the one that gets reduced

Question 8

reducing agent

Answer 8

gets oxidized

Question 9

oxidation number

Answer 9

elements start out with an oxidation number of zero

for ions composed of only one atom, the oxidation number is the charge on the ion

Question 10

oxidation number of oxygen

Answer 10

is mostly -2 even if its covalent

Exception:

Perioxides (R2O2) has a charge of -1

Question 11

oxidation number of hydrogen

Answer 11

is +1 whether its ionic or covalent

exceptions:

when Hydrogen is bound to a binary metal ex. NaH, it has an oxidation number of -1

Question 12

fluorine oxidation number

Answer 12

has -1, as do most halogens

Question 13

exceptions to oxidation numbers

Answer 13

halogens other than fluorine is combined with oxygen to form an oxygen, the oxidation number becomes POSITIVE.

ClO- becomes +1 oxidation for Cl

Question 14

sum of oxidation number

Answer 14

must give charge of compound

ex. ClO2-

Cl is +3
O2 is -4

Question 15

electrons are -ve so…

Answer 15

if oxidation number for a specific atom becomes more +
- it lost electrons and is oxidized

if oxidation number for an atom becomes more -ve
- it gained electrons and is reduced

Question 16

how to balance redox eqns

Answer 16

• write out half reactions

Question 17

how to do half reaction

Answer 17

1) write unbalanced reaction in ionic form
2) separate ion into two reactions (one compound and its ions, and the other)
3) balance atoms other than o and H in each reaction separately, then add water to balance the O and H+
4) add electrons to one side of each half reaction to balance the charges
5) if needed, multiply both balanced reactions by an integer to equalize the number of electrons transferred in reactions
6) add them together and cancel identical species

Question 18

converting chemical energy into electrical energy

Answer 18

when reagents are mixed, the electron transfer occurs directly and no electrical work can be obtained

Question 19

electrical work

Answer 19

can be obtained through a movement of electrons through a wire.

• a spontaneous redox reaction produces electrical energy in a cell

Question 20

energy cells

Answer 20

are galvanic cells

Question 21

galvanic cells

Answer 21

1) solutions (cu and zn 2+?) are kept in separate containers called half cells.
2) electrode is dipped in each half cell. electrodes provide a surface for each of the chemical half-reactions to take place. these electrodes are made of the two metals involving Solid zinc, in zinc solution and solid copper in copper solution) or from a chemically inert metal such as plutonium
3) the oxidation container and redox container are connected by a wire. and the transfer of electrons occurs indirectly through the external wire

Question 22

galvanic cell reaction notes

Answer 22

as reaction continues on, the solid zinc will get smaller (oxidation, anode, +)

as reaction continues on, the solid copper will get larger (reduction, cathode, -)

voltmeter is attached to wire to measure stuff

Question 23

galvanic cell reaction without salt bridge (??)

Answer 23

as reactions take place, the zinc oxidizes and their are more ions in solution. the copper gets reduced and copper ions go into the metal. which would oppose electron flow and stop reaction as the anode is getting positive and the cathode is getting -ve

Question 24

galvanic cell design must contain

Answer 24

species in solution and concentration, electrode and what it is made of, direction of electrons, voltmeter, salt bridge, labels of cathode/anote and reduction/oxidation and half reaction enqs

Question 25

cell potential

Answer 25

• is cell electrical energy,
• measure of the force behind redox run
• E (cell potential) describes the ability of each reagent to donate or withdraw electrons

Question 26

cell potential depends on

Answer 26

chemical reaction and concentration of solutes and/or partial pressures of gases

Question 27

voltmeter

Answer 27

• measure cell potential
• requires the flow of electrons which is slightly lower
• part of the cell potential is used to overcome the resistance of the wires in the voltmeter
• will measure a potential that is less than the maximum cell potential

Question 28

shorthand notation

Answer 28

phase boundaries are represented by a: /

reactants are written before products

reduction is written on the right

ex.

Zn (s)/ ZN2+ (aq, 1 M) // Cu 2= ..

Reactants/Products//Reactants/Products

the double slash is the salt bridge.

Question 29

oxidation number notation

Answer 29

write the charge BEFORE THE number

ex. -1 vs 1- (this is charge)

Question 30

halogen-Ox ion charge (ex. ClO3-)

Answer 30

this will always have a charge of 1- overall

Question 31

standard electrode potential, E cell

Answer 31

reduction potential for each half cell can be found.

Question 32

E cell

Answer 32

E cell= E red + E ox

this describes the ability to gain or lose electrons compared to the standard hydrogen electrode

Question 33

standard hydrogen electrode (SHE)

Answer 33

you can’t measure the reduction potential of a single half cell since one half cell has to be connected to another half cell to work

solution was a relative scale by choosing the reduction potential of H+ as 0.000V

2H+ + 2e- –>—< (equilibrium) H2

Question 34

the She device

Answer 34

electrode is made of platinum, solution is of H+ and H2 gas is made so an inverted beaker or something captures the gas.

H+ is measured as pH to see whether a reduction or oxidation took place as high pH would mean low H+, equilibrium would shift right which is reduction.

reduction of H+ is reversible so the other half cell determines whether h+ is reduced or H2 oxidized. the evidence for this is the increase in H2 gas, high pressure or effervescence.

Question 35

Calculating cell potential

Answer 35

half cell with larger E red (greater potential for reduction) will be reduced

the other will be oxidized

e ox= -e red

Question 36

salt bridge

Answer 36

without the salt bridge:

solution is neutral at the start but the anode gets more +ve charge and the cathode is getting more -ve charge which is opposing electron flow.

With bridge:
the ions like K+ and NO3- seep into solutions and keep them neutral.

Question 37

anode charge

Answer 37

is negative

Question 38

cathode charge

Answer 38

is positive

Question 39

electron flow is from

Answer 39

anode to cathode

Question 40

go draw a galvanic cell with zinc and copper

Answer 40

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